Definition Of Biology

Biology
From Wikipedia, the free encyclopedia

Biology deals with the study of the many varieties of living organisms. Clockwise from top left: Salmonella typhimurium, Phascolarctos cinereus, Athyrium filix-femina, Amanita muscaria, Agalychnis callidryas, and Brachypelma smithi

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy.[1] Biology is a vast subject containing many subdivisions, topics, and disciplines. Among the most important topics are five unifying principles that can be said to be the fundamental axioms of modern biology:[2]

1. Cells are the basic unit of life
2. New species and inherited traits are the product of evolution
3. Genes are the basic unit of heredity
4. An organism regulates its internal environment to maintain a stable and constant condition
5. Living organisms consume and transform energy.

Subdisciplines of biology are recognized on the basis of the scale at which organisms are studied and the methods used to study them: biochemistry examines the rudimentary chemistry of life; molecular biology studies the complex interactions of systems of biological molecules; cellular biology examines the basic building block of all life, the cell; physiology examines the physical and chemical functions of the tissues, organs, and organ systems of an organism; and ecology examines how various organisms interact and associate with their environment.[3]

History
History of biology

Ernst Haeckel's Tree of Life (1879)

The term biology is derived from the Greek word βίος, bios, "life" and the suffix -λογία, -logia, "study of." It appears in German (as biologie) as early as 1791, and may be a back-formation from the older word amphibiology (meaning the study of amphibians) by deletion of the initial amphi-.

Although biology in its modern form is a relatively recent development, sciences related to and included within it have been studied since ancient times. Natural philosophy was studied as early as the ancient civilizations of Mesopotamia, Egypt, the Indian subcontinent, and China. However, the origins of modern biology and its approach to the study of nature are most often traced back to ancient Greece.[4] While the formal study of medicine dates back to Hippocrates (ca. 460 BC – ca. 370 BC), it was Aristotle (384 BC – 322 BC) who contributed most extensively to the development of biology. Especially important are his History of Animals and other works where he showed naturalist leanings, and later more empirical works that focused on biological causation and the diversity of life. Aristotle's successor at the Lyceum, Theophrastus, wrote a series of books on botany that survived as the most important contribution of antiquity to the plant sciences, even into the Middle Ages.

Scholars of the medieval Islamic world who wrote on biology included al-Jahiz (781–869), Al-Dinawari (828–896), who wrote on botany,[5] and Rhazes (865–925) who wrote on anatomy and physiology. Medicine was especially well studied by Islamic scholars working in Greek philosopher traditions, while natural history drew heavily on Aristotelian thought, especially in upholding a fixed hierarchy of life.

Biology began to quickly develop and grow with Antony van Leeuwenhoek's dramatic improvement of the microscope. It was then that scholars discovered spermatozoa, bacteria, infusoria and the sheer strangeness and diversity of microscopic life. Investigations by Jan Swammerdam led to new interest in entomology and built the basic techniques of microscopic dissection and staining.[6]

Advances in microscopy also had a profound impact on biological thinking itself. In the early 19th century, a number of biologists pointed to the central importance of the cell. In 1838 and 1839, Schleiden and Schwann began promoting the ideas that (1) the basic unit of organisms is the cell and (2) that individual cells have all the characteristics of life, although they opposed the idea that (3) all cells come from the division of other cells. Thanks to the work of Robert Remak and Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of what came to be known as cell theory.[7]

Meanwhile, taxonomy and classification became a focus in the study of natural history. Carolus Linnaeus published a basic taxonomy for the natural world in 1735 (variations of which have been in use ever since), and in the 1750s introduced scientific names for all his species.[8] Georges-Louis Leclerc, Comte de Buffon, treated species as artificial categories and living forms as malleable—even suggesting the possibility of common descent. Though he was opposed to evolution, Buffon is a key figure in the history of evolutionary thought; his work influenced the evolutionary theories of both Lamarck and Darwin.[9]

Serious evolutionary thinking originated with the works of Jean-Baptiste Lamarck. However, it was the British naturalist Charles Darwin, combining the biogeographical approach of Humboldt, the uniformitarian geology of Lyell, Thomas Malthus's writings on population growth, and his own morphological expertise, that created a more successful evolutionary theory based on natural selection; similar reasoning and evidence led Alfred Russel Wallace to independently reach the same conclusions.[10]

The discovery of the physical representation of heredity came along with evolutionary principles and population genetics. In the 1940s and early 1950s, experiments pointed to DNA as the component of chromosomes that held genes. A focus on new model organisms such as viruses and bacteria, along with the discovery of the double helical structure of DNA in 1953, marked the transition to the era of molecular genetics. From the 1950s to present times, biology has been vastly extended in the molecular domain. The genetic code was cracked by Har Gobind Khorana, Robert W. Holley and Marshall Warren Nirenberg after DNA was understood to contain codons. Finally, the Human Genome Project was launched in 1990 with the goal of mapping the general human genome. This project was essentially completed in 2003,[11] with further analysis still being published. The Human Genome Project was the first step in a globalized effort to incorporate accumulated knowledge of biology into a functional, molecular definition of the human body and the bodies of other organisms.
Foundations of modern biology

Much of modern biology can be encompassed within five unifying principles: cell theory, evolution, genetics, homeostasis, and energy.[2]
Cell theory
Cell theory
Cells in culture, stained for keratin (red) and DNA (green)

Cell theory states that the cell is the fundamental unit of life, and that all living things are composed of one or more cells or the secreted products of those cells (e.g. shells). All cells arise from other cells through cell division. In multicellular organisms, every cell in the organism's body derives ultimately from a single cell in a fertilized egg. The cell is also considered to be the basic unit in many pathological processes.[12] Additionally, the phenomenon of energy flow occurs in cells in processes that are part of the function known as metabolism. Finally, cells contain hereditary information (DNA) which is passed from cell to cell during cell division.
Evolution
Natural selection of a population for dark coloration.
Evolution

A central organizing concept in biology is that life changes and develops through evolution, and that all life-forms known have a common origin. Introduced into the scientific lexicon by Jean-Baptiste de Lamarck in 1809,[13] evolution was established by Charles Darwin fifty years later as a viable theory when he articulated its driving force: natural selection.[14][15] (Alfred Russel Wallace is recognized as the co-discoverer of this concept as he helped research and experiment with the concept of evolution.)[16] Evolution is now used to explain the great variations of life found on Earth.

Darwin theorized that species and breeds developed through the processes of natural selection and artificial selection or selective breeding.[17] Genetic drift was embraced as an additional mechanism of evolutionary development in the modern synthesis of the theory.[18]

The evolutionary history of the species—which describes the characteristics of the various species from which it descended—together with its genealogical relationship to every other species is known as its phylogeny. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of DNA sequences conducted within molecular biology or genomics, and comparisons of fossils or other records of ancient organisms in paleontology.[19] Biologists organize and analyze evolutionary relationships through various methods, including phylogenetics, phenetics, and cladistics. (For a summary of major events in the evolution of life as currently understood by biologists, see evolutionary timeline.)

The theory of evolution postulates that all organisms on the Earth, both living and extinct, have descended from a common ancestor or an ancestral gene pool. This last universal common ancestor of all organisms is believed to have appeared about 3.5 billion years ago.[20] Biologists generally regard the universality and ubiquity of the genetic code as definitive evidence in favor of the theory of universal common descent for all bacteria, archaea, and eukaryotes (see: origin of life).[21]
Genetics
Genetics
A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms

Genes are the primary units of inheritance in all organisms. A gene is a unit of heredity and corresponds to a region of DNA that influences the form or function of an organism in specific ways. All organisms, from bacteria to animals, share the same basic machinery that copies and translates DNA into proteins. Cells transcribe a DNA gene into an RNA version of the gene, and a ribosome then translates the RNA into a protein, a sequence of amino acids. The translation code from RNA codon to amino acid is the same for most organisms, but slightly different for some. For example, a sequence of DNA that codes for insulin in humans also codes for insulin when inserted into other organisms, such as plants.[22][23]

DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. A chromosome is an organized structure consisting of DNA and histones. The set of chromosomes in a cell and any other hereditary information found in the mitochondria, chloroplasts, or other locations is collectively known as its genome. In eukaryotes, genomic DNA is located in the cell nucleus, along with small amounts in mitochondria and chloroplasts. In prokaryotes, the DNA is held within an irregularly shaped body in the cytoplasm called the nucleoid.[24] The genetic information in a genome is held within genes, and the complete assemblage of this information in an organism is called its genotype.[25]
Homeostasis
Homeostasis
The hypothalamus secretes CRH, which directs the pituitary gland to secrete ACTH. In turn, ACTH directs the adrenal cortex to secrete glucocorticoids, such as cortisol. The GCs then reduce the rate of secretion by the hypothalamus and the pituitary gland once a sufficient amount of GCs has been released.[26]

Homeostasis is the ability of an open system to regulate its internal environment to maintain stable conditions by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular, exhibit homeostasis.[27]

To maintain dynamic equilibrium and effectively carry out certain functions, a system must detect and respond to perturbations. After the detection of a perturbation, a biological system normally respond through negative feedback. This means stabilizing conditions by either reducing or increasing the activity of an organ or system. One example is the release of glucagon when sugar levels are too low.
Energy
Basic overview of energy and human life.

The survival of a living organism depends on the continuous input of energy. Chemical reactions that are responsible for its structure and function are tuned to extract energy from substances that act as its food and transform them to help form new cells and sustain them. In this process, molecules of chemical substances that constitute food play two roles; first, they contain energy that can be transformed for biological chemical reactions; second, they develop new molecular structures made up of biomolecules.

The organisms responsible for the introduction of energy into an ecosystem are known as producers or autotrophs. Nearly all of these organisms originally draw energy from the sun.[28] Plants and other phototrophs use solar energy via a process known as photosynthesis to convert raw materials into organic molecules, such as ATP, whose bonds can be broken to release energy.[29] A few ecosystems, however, depend entirely on energy extracted by chemotrophs from methane, sulfides, or other non-luminal energy sources.[30]

Some of the captured energy is used to produce biomass to sustain life and provide energy for growth and development. The majority of the rest of this energy is lost as heat and waste molecules. The most important processes for converting the energy trapped in chemical substances into energy useful to sustain life are metabolism[31] and cellular respiration.[32]
Research
Structural
Schematic of typical animal cell depicting the various organelles and structures.
Main articles: Molecular biology, Cell biology, Genetics, and Developmental biology

Molecular biology is the study of biology at a molecular level.[33] This field overlaps with other areas of biology, particularly with genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA, and protein synthesis and learning how these interactions are regulated.

Cell biology studies the structural and physiological properties of cells, including their behaviors, interactions, and environment. This is done on both the microscopic and molecular levels, for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans. Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology.

Anatomy considers the forms of macroscopic structures such as organs and organ systems.[34]

Genetics is the science of genes, heredity, and the variation of organisms.[35][36] Genes encode the information necessary for synthesizing proteins, which in turn play a large role in influencing (though, in many instances, not completely determining) the final phenotype of the organism. In modern research, genetics provides important tools in the investigation of the function of a particular gene, or the analysis of genetic interactions. Within organisms, genetic information generally is carried in chromosomes, where it is represented in the chemical structure of particular DNA molecules.

Developmental biology studies the process by which organisms grow and develop. Originating in embryology, modern developmental biology studies the genetic control of cell growth, differentiation, and "morphogenesis," which is the process that progressively gives rise to tissues, organs, and anatomy. Model organisms for developmental biology include the round worm Caenorhabditis elegans,[37] the fruit fly Drosophila melanogaster,[38] the zebrafish Danio rerio,[39] the mouse Mus musculus,,[40] and the weed Arabidopsis thaliana.[41][42] (A model organism is a species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in that organism provide insight into the workings of other organisms.)[43]
Physiological
Physiology

Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but some principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Plant physiology borrows techniques from both research fields.

Physiology studies how for example nervous, immune, endocrine, respiratory, and circulatory systems, function and interact. The study of these systems is shared with medically oriented disciplines such as neurology and immunology.
Evolutionary

Evolutionary research is concerned with the origin and descent of species, as well as their change over time, and includes scientists from many taxonomically oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy, ornithology, botany, or herpetology, but use those organisms as systems to answer general questions about evolution.

Evolutionary biology is partly based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution,[44] and partly on the developments in areas such as population genetics[45] and evolutionary theory. In the 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology.[46] Related fields often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy.
Systematics
A phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains bacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains are still being debated.
Systematics

Multiple speciation events create a tree structured system of relationships between species. The role of systematics is to study these relationships and thus the differences and similarities between species and groups of species.[47] However, systematics was an active field of research long before evolutionary thinking was common.[48] The classification, taxonomy, and nomenclature of biological organisms is administered by the International Code of Zoological Nomenclature, International Code of Botanical Nomenclature, and International Code of Nomenclature of Bacteria for animals, plants, and bacteria, respectively. The classification of viruses, viroids, prions, and all other sub-viral agents that demonstrate biological characteristics is conducted by the International Code of Virus classification and nomenclature.[49][50][51][52] However, several other viral classification systems do exist.

Traditionally, living things have been divided into five kingdoms: Monera; Protista; Fungi; Plantae; Animalia.[53]

However, many scientists now consider this five-kingdom system outdated. Modern alternative classification systems generally begin with the three-domain system: Archaea (originally Archaebacteria); Bacteria (originally Eubacteria); Eukaryota (including protists, fungi, plants, and animals)[54] These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors.[54]

Further, each kingdom is broken down recursively until each species is separately classified. The order is: Domain; Kingdom; Phylum; Class; Order; Family; Genus; Species.

There is also a series of intracellular parasites that are "on the edge of life"[55] in terms of metabolic activity, meaning that many scientists do not actually classify these structures as alive, due to their lack of at least one or more of the fundamental functions that define life. They are classified as viruses, viroids, prions, or satellites.

The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens. Homo is the genus, and sapiens the species. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the species in lowercase. Additionally, the entire term may be italicized or underlined.[56][57]

The dominant classification system is called the Linnaean taxonomy. It includes ranks and binomial nomenclature. How organisms are named is governed by international agreements such as the International Code of Botanical Nomenclature (ICBN), the International Code of Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB).

A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature in these three areas, but has yet to be formally adopted.[58] The BioCode draft has received little attention since 1997; its originally planned implementation date of January 1, 2000, has passed unnoticed. However, a 2004 paper concerning the cyanobacteria does advocate a future adoption of a BioCode and interim steps consisting of reducing the differences between the codes.[59] The International Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.
Ecology
Mutual symbiosis between clownfish of the genus Amphiprion that dwell among the tentacles of tropical sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protects the clown fish from its predators
Main articles: Ecology, Ethology, Behavior, and Biogeography

Ecology studies the distribution and abundance of living organisms, and the interactions between organisms and their environment.[60] The habitat of an organism can be described as the local abiotic factors such as climate and ecology, in addition to the other organisms and biotic factors that share its environment.[61] One reason that biological systems can be difficult to study is that so many different interactions with other organisms and the environment are possible, even on the smallest of scales. A microscopic bacterium responding to a local sugar gradient is responding to its environment as much as a lion is responding to its environment when it searches for food in the African savanna. For any given species, behaviors can be co-operative, aggressive, parasitic, or symbiotic. Matters become more complex when two or more different species interact in an ecosystem. Studies of this type are within the province of ecology.

Ecological systems are studied at several different levels, from individuals and populations to ecosystems and the biosphere. The term population biology is often used interchangeably with population ecology, although population biology is more frequently used when studying diseases, viruses, and microbes, while population ecology is more commonly when studying plants and animals. As can be surmised, ecology is a science that draws on several disciplines.

Ethology studies animal behavior (particularly that of social animals such as primates and canids), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book, The Expression of the Emotions in Man and Animals, influenced many ethologists to come.[62]

Biogeography studies the spatial distribution of organisms on the Earth,[63] focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics.
Branches of biology

These are the main branches of biology:[64][65]

* Aerobiology — the study of airborne organic particles
* Agriculture — the study of producing crops from the land, with an emphasis on practical applications
* Anatomy — the study of form and function, in plants, animals, and other organisms, or specifically in humans
* Arachnology — the study of arachnids
* Astrobiology — the study of evolution, distribution, and future of life in the universe—also known as exobiology, exopaleontology, and bioastronomy
* Biochemistry — the study of the chemical reactions required for life to exist and function, usually a focus on the cellular level
* Bioengineering — the study of biology through the means of engineering with an emphasis on applied knowledge and especially related to biotechnology
* Biogeography — the study of the distribution of species spatially and temporally
* Bioinformatics — the use of information technology for the study, collection, and storage of genomic and other biological data
* Biomathematics or Mathematical Biology — the quantitative or mathematical study of biological processes, with an emphasis on modeling
* Biomechanics — often considered a branch of medicine, the study of the mechanics of living beings, with an emphasis on applied use through prosthetics or orthotics
* Biomedical research — the study of the human body in health and disease
* Biophysics — the study of biological processes through physics, by applying the theories and methods traditionally used in the physical sciences
* Biotechnology — a new and sometimes controversial branch of biology that studies the manipulation of living matter, including genetic modification and synthetic biology
* Building biology — the study of the indoor living environment
* Botany — the study of plants
* Cell biology — the study of the cell as a complete unit, and the molecular and chemical interactions that occur within a living cell
* Conservation Biology — the study of the preservation, protection, or restoration of the natural environment, natural ecosystems, vegetation, and wildlife
* Cryobiology — the study of the effects of lower than normally preferred temperatures on living beings.
* Developmental biology — the study of the processes through which an organism forms, from zygote to full structure
* Ecology — the study of the interactions of living organisms with one another and with the non-living elements of their environment
* Embryology — the study of the development of embryo (from fecundation to birth). See also topobiology.
* Entomology — the study of insects
* Environmental Biology — the study of the natural world, as a whole or in a particular area, especially as affected by human activity
* Epidemiology — a major component of public health research, studying factors affecting the health of populations
* Ethology — the study of animal behavior
* Evolutionary Biology — the study of the origin and descent of species over time
* Genetics — the study of genes and heredity
* Herpetology — the study of reptiles and amphibians
* Histology — the study of cells and tissues, a microscopic branch of anatomy
* Ichthyology — the study of fish
* Integrative biology — the study of whole organisms
* Limnology — the study of inland waters
* Mammalogy — the study of mammals
* Marine Biology — the study of ocean ecosystems, plants, animals, and other living beings
* Microbiology — the study of microscopic organisms (microorganisms) and their interactions with other living things
* Molecular Biology — the study of biology and biological functions at the molecular level, some cross over with biochemistry
* Mycology — the study of fungi
* Neurobiology — the study of the nervous system, including anatomy, physiology and pathology
* Oceanography — the study of the ocean, including ocean life, environment, geography, weather, and other aspects influencing the ocean
* Oncology — the study of cancer processes, including virus or mutation oncogenesis, angiogenesis and tissues remoldings
* Ornithology — the study of birds
* Population biology — the study of groups of conspecific organisms, including
o Population ecology — the study of how population dynamics and extinction
o Population genetics — the study of changes in gene frequencies in populations of organisms
* Paleontology — the study of fossils and sometimes geographic evidence of prehistoric life
* Pathobiology or pathology — the study of diseases, and the causes, processes, nature, and development of disease
* Parasitology — the study of parasites and parasitism
* Pharmacology — the study and practical application of preparation, use, and effects of drugs and synthetic medicines
* Physiology — the study of the functioning of living organisms and the organs and parts of living organisms
* Phytopathology — the study of plant diseases (also called Plant Pathology)
* Psychobiology — the study of the biological bases of psychology
* Sociobiology — the study of the biological bases of sociology
* Structural biology — a branch of molecular biology, biochemistry, and biophysics concerned with the molecular structure of biological macromolecules
* Virology — the study of viruses and some other virus-like agents
* Zoology — the study of animals, including classification, physiology, development, and behavior (See also Entomology, Ethology, Herpetology, Ichthyology, Mammalogy, and Ornithology)

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Definition Of Geology

Geology
From Wikipedia, the free encyclopedia

Geology (from the Greek γῆ, gê, "earth" and λόγος, logos, "study") is the science comprising the study of solid Earth and the processes by which it evolves. Geology provides primary evidence for plate tectonics, the history of life and evolution, and past climates. In modern times, geology is commercially important for mineral and hydrocarbon exploration and for evaluating water resources; is publicly important for the prediction and understanding of natural hazards, the remediation of environmental problems, and for providing insights into past climate change; plays an essential role in geotechnical engineering; and is a major academic discipline.


 History
Main article: History of geology

William Smith's geologic map of England, Wales, and southern Scotland. Completed in 1815, it was the first national-scale geologic map, and by far the most accurate of its time.[1]

The study of the physical material of the Earth dates back at least to ancient Greece when Theophrastus (372-287 BC) wrote the work Peri Lithon (On Stones). In the Roman period, Pliny the Elder wrote in detail of the many minerals and metals then in practical use, and correctly noted the origin of amber.

Some modern scholars, such as Fielding H. Garrison, are of the opinion that modern geology began in the medieval Islamic world.[2] Abu al-Rayhan al-Biruni (973–1048 AD) was one of the earliest Muslim geologists, whose works included the earliest writings on the geology of India, hypothesizing that the Indian subcontinent was once a sea.[3][verification needed] Islamic Scholar Ibn Sina (Avicenna, 981–1037) proposed detailed explanations for the formation of mountains, the origin of earthquakes, and other topics central to modern Geology, which provided an essential foundation for the later development of the science.[4][verification needed] In China, the polymath Shen Kua (1031–1095) formulated a hypothesis for the process of land formation: based on his observation of fossil animal shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by erosion of the mountains and by deposition of silt.[citation needed]

Nicolas Steno (1638–1686) is credited with the law of superposition, the principle of original horizontality, and the principle of lateral continuity: three defining principles of stratigraphy.

The word geology was first used by Ulisse Aldrovandi in 1603,[5] then by Jean-André Deluc in 1778 and introduced as a fixed term by Horace-Bénédict de Saussure in 1779. The word is derived from the Greek γῆ, gê, meaning "earth" and λόγος, logos, meaning "speech".[6] But according to another source, the word "Geology" comes from the Norwegian, Mikkel Pedersøn Escholt (1600–1699), who was a priest and scholar. Escholt was first used the definition in his book titled, Geologica Norvegica (1657).[7]

William Smith (1769–1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them.[1]

James Hutton is often viewed as the first modern geologist.[8] In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795 (Vol. 1, Vol. 2).

Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism, which is the deposition of lava from volcanoes, as opposed to the Neptunists, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time.

Sir Charles Lyell first published his famous book, Principles of Geology,[9] in 1830. The book, which influenced the thought of Charles Darwin, successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time.

Much of 19th-century geology revolved around the question of the Earth's exact age. Estimates varied from a few 100,000 to billions of years.[10] By the early 20th century, radiometric dating allowed the Earth's age to be estimated at two billion years. The awareness of this vast amount of time opened the door to new theories about the processes that shaped the planet.

The most significant advances in 20th century geology have been the development of the theory of plate tectonics in the 1960s, and the refinement of estimates of the planet's age. Plate tectonic theory arose out of two separate geological observations: seafloor spreading and continental drift. The theory revolutionized the Earth sciences. Today the Earth is known to be approximately 4.5 billion years old.[11]
 Geologic time

Geological time put in a diagram called a geological clock, showing the relative lengths of the eons of the Earth's history.
Main articles: History of the Earth and Geologic time scale

The geologic time scale encompasses the history of the Earth.[12] It is bracketed at the old end by the dates of the earliest solar system material at 4.567 Ga,[13] (gigaannum: billion years ago) and the age of the Earth at 4.54 Ga[14][15] at the beginning of the informally recognized Hadean eon. At the young end of the scale, it is bracketed by the present day in the Holocene epoch.
 Important milestones

    * 4.567 Ga: Solar system formation[13]
    * 4.54 Ga: Accretion of Earth[14][15]
    * c. 4 Ga: End of Late Heavy Bombardment, first life
    * c. 3.5 Ga: Start of photosynthesis
    * c. 2.3 Ga: Oxygenated atmosphere, first snowball Earth
    * 730–635 Ma (megaannum: million years ago): two snowball Earths
    * 542± 0.3 Ma: Cambrian explosion – vast multiplication of hard-bodied life; first abundant fossils; start of the Paleozoic
    * c. 380 Ma: First vertebrate land animals
    * 250 Ma: Permian-Triassic extinction – 90% of all land animals die. End of Paleozoic and beginning of Mesozoic
    * 65 Ma: Cretaceous-Tertiary extinction – Dinosaurs die; end of Mesozoic and beginning of Cenozoic
    * c. 7 Ma – Present: Hominins
          o c. 7 Ma: First hominins appear
          o 3.9 Ma: First Australopithecus, direct ancestor to modern Homo sapiens, appear
          o 200 ka (kiloannum: thousand years ago): First modern Homo sapiens appear in East Africa

 Brief time scale

The second and third timelines are each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on this timeline.

Millions of Years
 Relative and absolute dating

Geological events can be given a precise date at a point in time, or they can be related to other events that came before and after them. Geologists use a variety of methods to give both relative and absolute dates to geological events. They then use these dates to find the rates at which processes occur.
 Relative dating
Main article: Relative dating
Cross-cutting relations can be used to determine the relative ages of rock strata and other geological structures. Explanations: A - folded rock strata cut by a thrust fault; B - large intrusion (cutting through A); C - erosional angular unconformity (cutting off A & B) on which rock strata were deposited; D - volcanic dyke (cutting through A, B & C); E - even younger rock strata (overlying C & D); F - normal fault (cutting through A, B, C & E).

Methods for relative dating were developed when geology first emerged as a formal science. Geologists still use the following principles today as a means to provide information about geologic history and the timing of geologic events.

The principle of intrusive relationships concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills and dikes.

The principle of cross-cutting relationships pertains to the formation of faults and the age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault. Finding the key bed in these situations may help determine whether the fault is a normal fault or a thrust fault.[16]

The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them.

The principle of uniformitarianism states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time.[17] A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now."[citation needed]
The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of both Original Horizontality and the Law of Superposition. These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park. From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone. Picture from Glen Canyon National Recreation Area, Utah.

The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal).[16]

The principle of superposition states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed.[16]

The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by William Smith almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, the localization of fossil types due to lateral changes in habitat (facies change in sedimentary strata), and that not all fossils may be found globally at the same time.[18]
 Absolute dating
Main articles: Absolute dating, Radiometric dating, and Geochronology

Geologists can also give precise absolute dates to geologic events. These dates are useful on their own, and can also be used in conjunction with relative dating methods or to calibrate relative dating methods.[19]

A large advance in geology in the advent of the 20th century was the ability to give precise absolute dates to geologic events through radioactive isotopes and other methods. The advent of radiometric dating changed the understanding of geologic time. Before, geologists could only use fossils to date sections of rock relative to one another. With isotopic dates, absolute dating became possible, and these absolute dates could be applied fossil sequences in which there was datable material, converting the old relative ages into new absolute ages.

For many geologic applications, isotope ratios are measured in minerals that give the amount of time that has passed since a rock passed through its particular closure temperature, the point at which different radiometric isotopes stop diffusing into and out of the crystal lattice.[20][21] These are used in geochronologic and thermochronologic studies. Common methods include uranium-lead dating, potassium-argon dating and argon-argon dating, and uranium-thorium dating. These methods are used for a variety of applications. Dating of lavas and ash layers can help to date stratigraphy and calibrate relative dating techniques. These methods can also be used to determine ages of pluton emplacement. Thermochemical techniques can be used to determine temperature proiles within the crust, the uplift of mountain ranges, and paleotopography.

Fractionation of the lanthanide series elements is used to compute ages since rocks were removed from the mantle.

Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionucleide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for the dating of landscapes. Radiocarbon dating is used for young organic material.
 Geologic materials

The majority of geological data come from research on solid Earth materials. These typically fall into one of two categories: rock and unconsolidated material.
 Rock
This schematic diagram of the rock cycle shows the relationship between magma and sedimentary, metamorphic, and igneous rock
Main articles: Rock (geology) and Rock cycle

There are three major types of rock: igneous, sedimentary, and metamorphic. The rock cycle is an important concept in geology which illustrates the relationships between these three types of rock, and magma. When a rock crystallizes from melt (magma and/or lava), it is an igneous rock. This rock can be weathered and eroded, and then redeposited and lithified into a sedimentary rock, or be turned into a metamorphic rock due to heat and pressure that change the mineral content of the rock and give it a characteristic fabric. The sedimentary rock can then be subsequently turned into a metamorphic rock due to heat and pressure, and the metamorphic rock can be weathered, eroded, deposited, and lithified, becoming a sedimentary rock. Sedimentary rock may also be re-eroded and redeposited, and metamorphic rock may also undergo additional metamorphism. All three types of rocks may be re-melted; when this happens, a new magma is formed, from which an igneous rock may once again crystallize.

The majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth.
 Unconsolidated material

Geologists also study unlithified material, which typically comes from more recent deposits. Because of this, the study of such material is often known as Quaternary geology, after the recent Quaternary Period. This includes the study of sediment and soils, and is important to some (or many) studies in geomorphology, sedimentology, and paleoclimatology.
 Whole-Earth structure
Oceanic-continental convergence resulting in subduction and volcanic arcs illustrates one effect of plate tectonics.
 Plate tectonics
Main article: Plate tectonics
On this diagram, subducting slabs are in blue, and continental margins and a few plate boundaries are in red. The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America. The remnants of this plate on the Surface of the Earth are the Juan de Fuca Plate and Explorer plate in the Northwestern USA / Southwestern Canada, and the Cocos Plate on the west coast of Mexico.

In the 1960s, a series of discoveries, the most important of which was seafloor spreading,[22][23] showed that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into a number of tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere. There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle: oceanic plate motions and mantle convection currents always move in the same direction, because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle. This coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics.

The development of plate tectonics provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries.[24] Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, were explained as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes were explained as convergent boundaries, where one plate subducts under another. Transform boundaries, such as the San Andreas fault system, resulted in widespread powerful earthquakes. Plate tectonics also provided a mechanism for Alfred Wegener's theory of continental drift,[25] in which the continents move across the surface of the Earth over geologic time. They also provided a driving force for crustal deformation, and a new setting for the observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convecting mantle.
 Earth structure
Main article: Structure of the Earth
The Earth's layered structure. (1) inner core; (2) outer core; (3) lower mantle; (4) upper mantle; (5) lithosphere; (6) crust
Earth layered structure. Typical wave paths from earthquakes like these gave early seismologists insights into the layered structure of the Earth

Advances in seismology, computer modeling, and mineralogy and crystallography at high temperatures and pressures give insights into the internal composition and structure of the Earth.

Seismologists can use the arrival times of seismic waves in reverse to image the interior of the Earth. Early advances in this field showed the existence of a liquid outer core (where shear waves were not able to propagate) and a dense solid inner core. These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that. More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan. These images have led to a much more detailed view of the interior of the Earth, and have replaced the simplified layered model with a much more dynamic model.

Mineralogists have been able to use the pressure and temperature data from the seismic and modelling studies alongside knowledge of the elemental composition of the Earth at depth to reproduce these conditions in experimental settings and measure changes in crystal structure. These studies explain the chemical changes associated with the major seismic discontinuities in the mantle, and show the crystallographic structures expected in the inner core of the Earth.
 Geological evolution of an area
An originally horizontal sequence of sedimentary rocks (in shades of tan) are affected by igneous activity. Deep below the surface are a magma chamber and large associated igneous bodies. The magma chamber feeds the volcano, and sends off shoots of magma that will later crystallize into dikes and sills. Magma also advances upwards to form intrusive igneous bodies. The diagram illustrates both a cinder cone volcano, which releases ash, and a composite volcano, which releases both lava and ash.
An illustration of the three types of faults. Strike-slip faults occur when rock units slide past one another, normal faults occur when rocks are undergoing horizontal extension, and thrust faults occur when rocks are undergoing horizontal shortening.

The geology of an area evolves through time as rock units are deposited and inserted and deformational processes change their shapes and locations.

Rock units are first emplaced either by deposition onto the surface or intrusion into the overlying rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows blanket the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and sills, push upwards into the overlying rock, and crystallize as they intrude.

After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to convergent boundaries, divergent boundaries, and transform boundaries, respectively, between tectonic plates.

When rock units are placed under horizontal compression, they shorten and become thicker. Because rock units, other than muds, do not significantly change in volume, this is accomplished in two primary ways: through faulting and folding. In the shallow crust, where brittle deformation can occur, thrust faults form, which cause deeper rock to move on top of shallower rock. Because deeper rock is often older, as noted by the principle of superposition, this can result in older rocks moving on top of younger ones. Movement along faults can result in folding, either because the faults are not planar, or because the rock layers are dragged along, forming drag folds, as slip occurs are along the fault. Deeper in the Earth, rocks behave plastically, and fold instead of faulting. These folds can either be those where the material in the center of the fold buckles upwards, creating "antiforms", or where it buckles downwards, creating "synforms". If the tops of the rock units within the folds remain pointing upwards, they are called anticlines and synclines, respectively. If some of the units in the fold are facing downward, the structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general terms, antiforms and synforms.
A diagram of folds, indicating an anticline and a syncline.

Even higher pressures and temperatures during horizontal shortening can cause both folding and metamorphism of the rocks. This metamorphism causes changes in the mineral composition of the rocks; creates a foliation, or planar surface, that is related to mineral growth under stress; and can remove signs of the original textures of the rocks, such as bedding in sedimentary rocks, flow features of lavas, and crystal patterns in crystalline rocks.

Extension causes the rock units as a whole to become longer and thinner. This is primarily accomplished through normal faulting and through the ductile stretching and thinning. Normal faults drop rock units that are higher below those that are lower. This typically results in younger units being placed below older units. Stretching of units can result in their thinning; in fact, there is a location within the Maria Fold and Thrust Belt in which the entire sedimentary sequence of the Grand Canyon can be seen over a length of less than a meter. Rocks at the depth to be ductilely stretched are often also metamorphosed. These stretched rocks can also pinch into lenses, known as boudins, after the French word for "sausage", because of their visual similarity.

Where rock units slide past one another, strike-slip faults develop in shallow regions, and become shear zones at deeper depths where the rocks deform ductilely.
Geologic cross-section of Kittatinny Mountain. This cross-section shows metamorphic rocks, overlain by younger sediments deposited after the metamorphic event. These rock units were later folded and faulted during the uplift of the mountain.

The addition of new rock units, both depositionally and intrusively, often occurs during deformation. Faulting and other deformational processes result in the creation of topographic gradients, causing material on the rock unit that is increasing in elevation to be eroded by hillslopes and channels. These sediments are deposited on the rock unit that is going down. Continual motion along the fault maintains the topographic gradient in spite of the movement of sediment, and continues to create accommodation space for the material to deposit. Deformational events are often also associated with volcanism and igneous activity. Volcanic ashes and lavas accumulate on the surface, and igneous intrusions enter from below. Dikes, long, planar igneous intrusions, enter along cracks, and therefore often form in large numbers in areas that are being actively deformed. This can result in the emplacement of dike swarms, such as those that are observable across the Canadian shield, or rings of dikes around the lava tube of a volcano.

All of these processes do not necessarily occur in a single environment, and do not necessarily occur in a single order. The Hawaiian Islands, for example, consist almost entirely of layered basaltic lava flows. The sedimentary sequences of the mid-continental United States and the Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since Cambrian time. Other areas are much more geologically complex. In the southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the Acasta gneiss of the Slave craton in northwestern Canada, the oldest known rock in the world have been metamorphosed to the point where their origin is undiscernable without laboratory analysis. In addition, these processes can occur in stages. In many places, the Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the geological history of an area.
 Methods of geology

Geologists use a number of field, laboratory, and numerical modeling methods to decipher Earth history and understand the processes that occur on and in the Earth. In typical geological investigations, geologists use primary information related to petrology (the study of rocks), stratigraphy (the study of sedimentary layers), and structural geology (the study of positions of rock units and their deformation). In many cases, geologists also study modern soils, rivers, landscapes, and glaciers; investigate past and current life and biogeochemical pathways, and use geophysical methods to investigate the subsurface.
Washington State Land Forms
 Field methods
A standard Brunton Geo compass, used commonly by geologists in mapping and surveying
A typical USGS field mapping camp in the 1950s
Today, handheld computers with GPS and geographic information systems software are often used in geological field work (digital geologic mapping).

Geological field work varies depending on the task at hand. Typical fieldwork could consist of:

    * Geological mapping[26]
          o Structural mapping: the locations of the major rock units and the faults and folds that led to their placement there.
          o Stratigraphic mapping: the locations of sedimentary facies (lithofacies and biofacies) or the mapping of isopachs of equal thickness of sedimentary rock
          o Surficial mapping: the locations of soils and surficial deposits
    * Surveying of topographic features
          o Creation of topographic maps[27]
          o Work to understand change across landscapes, including:
                + Patterns of erosion and deposition
                + River channel change through migration and avulsion
                + Hillslope processes
    * Subsurface mapping through geophysical methods[28]
          o These methods include:
                + Shallow seismic surveys
                + Ground-penetrating radar
                + Electrical resistivity tomography
          o They are used for:
                + Hydrocarbon exploration
                + Finding groundwater
                + Locating buried archaeological artifacts
    * High-resolution stratigraphy
          o Measuring and describing stratigraphic sections on the surface
          o Well drilling and logging
    * Biogeochemistry and geomicrobiology[29]
          o Collecting samples to:
                + Determine biochemical pathways
                + Identify new species of organisms. These organisms may help to show:
                + Identify new chemical compounds
          o And to use these discoveries to
                + Understand early life on Earth and how it functioned and metabolized
                + Find important compounds for use in pharmaceuticals.
    * Paleontology: excavation of fossil material
          o For research into past life and evolution
          o For museums and education
    * Collection of samples for geochronology and thermochronology[30]
    * Glaciology: measurement of characteristics of glaciers and their motion[31]

 Laboratory methods
A petrographic microscope, which is a optical microscope fitted with cross-polarizing lenses, a conoscopic lens, and compensators (plates of anisotropic materials; gypsum plates and quartz wedges are common), for crystallographic analysis.
 Petrology
Main article: Petrology

In addition to the field identification of rocks, petrologists identify rock samples in the laboratory. Two of the primary methods for identifying rocks in the laboratory are through optical microscopy and by using an electron microprobe. In an optical mineralogy analysis, thin sections of rock samples are analyzed through a petrographic microscope, where the minerals can be identified through their different properties in plane-polarized and cross-polarized light, including their birefringence, pleochroism, twinning, and interference properties with a conoscopic lens.[32] In the electron microprobe, individual locations are analyzed for their exact chemical compositions and variation in composition within individual crystals.[33] Stable[34] and radioactive isotope[35] studies provide insight into the geochemical evolution of rock units.

Petrologists use fluid inclusion data[36] and perform high temperature and pressure physical experiments[37] to understand the temperatures and pressures at which different mineral phases appear, and how they change through igneous[38] and metamorphic processes. This research can be extrapolated to the field to understand metamorphic processes and the conditions of crystallization of igneous rocks.[39] This work can also help to explain processes that occur within the Earth, such as subduction and magma chamber evolution.
 Structural geology
A diagram of an orogenic wedge. The wedge grows through faulting in the interior and along the main basal fault, called the décollement. It builds its shape into a critical taper, in which the angles within the wedge remain the same as failures inside the material balance failures along the décollement. It is analogous to a bulldozer pushing a pile of dirt, where the bulldozer is the overriding plate.
Main article: Structural geology

Structural geologists use microscopic analysis of oriented thin sections of geologic samples to observe the fabric within the rocks which gives information about strain within the crystal structure of the rocks. They also plot and combine measurements of geological structures in order to better understand the orientations of faults and folds in order to reconstruct the history of rock deformation in the area. In addition, they perform analog and numerical experiments of rock deformation in large and small settings.

The analysis of structures is often accomplished by plotting the orientations various features onto stereonets. A stereonet is a stereographic projection of a sphere onto a plane, in which planes are projected as lines and lines are projected as points. These can be used to find the locations of fold axes, relationships between several faults, and relationships between other geologic structures.

Among the most well-known experiments in structural geology are those involving orogenic wedges, which are zones in which mountains are built along convergent tectonic plate boundaries.[40] In the analog versions of these experiments, horizontal layers of sand are pulled along a lower surface into a back stop, which results in realistic-looking patterns of faulting and the growth of a critically tapered (all angles remain the same) orogenic wedge.[41] Numerical models work in the same way as these analog models, though they are often more sophisticated and can include patterns of erosion and uplift in the mountain belt.[42] This helps to show the relationship between erosion and the shape of the mountain range. These studies can also give useful information about pathways for metamorphism through pressure, temperature, space, and time.[43]
 Stratigraphy
Main article: Stratigraphy
Exploration geologists examining a freshly recovered drill core. Chile, 1994

In the laboratory, stratigraphers analyze samples of stratigraphic sections that can be returned from the field, such as those from drill cores.[44] Stratigraphers also analyze data from geophysical surveys that show the locations of stratigraphic units in the subsurface.[45] Geophysical data and well logs can be combined to produce a better view of the subsurface, and stratigraphers often use computer programs to do this in three dimensions.[46] Stratigraphers can then use these data to reconstruct ancient processes occurring on the surface of the Earth,[47] interpret past environments, and locate areas for water, coal, and hydrocarbon extraction.

In the laboratory, biostratigraphers analyze rock samples from outcrop and drill cores for the fossils found in them.[44] These fossils help scientists to date the core and to understand the depositional environment in which the rock units formed. Geochronologists precisely date rocks within the stratigraphic section in order to provide better absolute bounds on the timing and rates of deposition.[48] Magnetic stratigraphers look for signs of magnetic reversals in igneous rock units within the drill cores.[44] Other scientists perform stable isotope studies on the rocks to gain information about past climate.[44]
 Planetary geology
Surface of Mars as photographed by the Viking 2 lander December 9, 1977.
Main articles: Planetary geology and Geology of solar terrestrial planets

With the advent of space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same way as the Earth. This led to the establishment of the field of planetary geology, sometimes known as astrogeology, in which geologic principles are applied to other bodies of the solar system.

Although the Greek-language-origin prefix geo refers to Earth, "geology" is often used in conjunction with the names of other planetary bodies when describing their composition and internal processes: examples are "the geology of Mars" and "Lunar geology". Specialised terms such as selenology (studies of the Moon), areology (of Mars), etc., are also in use.

Although planetary geologists are interested in all aspects of the planets, a significant focus is in the search for past or present life on other worlds. This has led to many missions whose purpose (or one of their purposes) is to examine planetary bodies for evidence of life. One of these is the Phoenix lander, which analyzed Martian polar soil for water and chemical and mineralogical constituents related to biological processes.
 Applied geology
 Economic geology
Main article: Economic geology

Economic geologists help locate and manage the Earth's natural resources, such as petroleum and coal, as well as mineral resources, which include metals such as iron, copper, and uranium.
 Mining geology
Main article: Mining

Mining geology consists of the extractions of mineral resources from the Earth. Some resources of economic interests include gemstones, metals, and many minerals such as asbestos, perlite, mica, phosphates, zeolites, clay, pumice, quartz, and silica, as well as elements such as sulfur, chlorine, and helium.
 Petroleum geology
Mud log in process, a common way to study the lithology when drilling oil wells.
Main article: Petroleum geology

Petroleum geologists study locations of the subsurface of the Earth which can contain extractable hydrocarbons, especially petroleum and natural gas. Because many of these reservoirs are found in sedimentary basins,[49] they study the formation of these basins, as well as their sedimentary and tectonic evolution and the present-day positions of the rock units.
 Engineering geology
Main articles: Engineering geology, Soil mechanics, and Geotechnical engineering

Engineering geology is the application of the geologic principles to engineering practice for the purpose of assuring that the geologic factors affecting the location, design, construction, operation and maintenance of engineering works are properly addressed.

In the field of civil engineering, geological principles and analyses are used in order to ascertain the mechanical principles of the material on which structures are built. This allows tunnels to be built without collapsing, bridges and skyscrapers to be built with sturdy foundations, and buildings to be built that will not settle in clay and mud.[50]
 Hydrology and environmental issues
Main article: Hydrogeology

Geology and geologic principles can be applied to various environmental problems, such as stream restoration, the restoration of brownfields, and the understanding of the interactions between natural habitat and the geologic environment. Groundwater hydrology, or hydrogeology, is used to locate groundwater,[51] which can often provide a ready supply of uncontaminated water and is especially important in arid regions,[52] and to monitor the spread of contaminants in groundwater wells.[51][53]

Geologists also obtain data through stratigraphy, boreholes, core samples, and ice cores. Ice cores[54] and sediment cores[55] are used to for paleoclimate reconstructions, which tell geologists about past and present temperature, precipitation, and sea level across the globe. These data are our primary source of information on global climate change outside of instrumental data.[56]

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Definition Of Physics

Physics
From Wikipedia, the free encyclopedia

Physics (from Ancient Greek: φύσις physis "nature") is a natural science that involves the study of matter[1] and its motion through spacetime, along with related concepts such as energy and force.[2] More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.[3][4][5]

Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy.[6] Over the last two millennia, physics was a part of natural philosophy along with chemistry, certain branches of mathematics, and biology, but during the Scientific Revolution in the 16th century, the natural sciences emerged as unique research programs in their own right.[7] Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. Indeed, new ideas in physics often explain the fundamental mechanisms of other sciences, while opening new avenues of research in areas such as mathematics and philosophy.

Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs. For example, advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products which have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus.

History
Isaac Newton (1643–1727)
Albert Einstein (1879-1955)
Main article: History of physics

As noted below, the means used to understand the behavior of natural phenomena and their effects evolved from philosophy, progressively replaced by natural philosophy then natural science, to eventually arrive at the modern conception of physics.[citation needed]

Natural philosophy has its origins in Greece during the Archaic period, (650 BCE – 480 BCE), when Pre-Socratic philosophers like Thales refused supernatural, religious or mythological explanations for natural phenomena and proclaimed that every event had a natural cause.[8] They proposed ideas verified by reason and observation and many of their hypotheses proved successful in experiment,[9] for example atomism.

Natural science was developed in China, India and in Islamic caliphates, between the 4th and 10th century BCE. Quantitative descriptions became popular among physicists and astronomers, for example Archimedes in the domains of mechanics, statics and hydrostatics. Experimental physics had its debuts with experimentation concerning statics by medieval Muslim physicists like al-Biruni and Alhazen.[10][11]

Classical physics became a separate science when early modern Europeans used these experimental and quantitative methods to discover what are now considered to be the laws of physics.[12][13] Kepler, Galileo and more specifically Newton discovered and unified the different laws of motion.[14] During the industrial revolution, as energy needs increased, so did research, which led to the discovery of new laws in thermodynamics, chemistry and electromagnetics.

Modern physics started with the works of Einstein both in relativity and quantum physics.[citation needed]
Philosophy

In many ways, physics stems from ancient Greek philosophy. From Thales' first attempt to characterize matter, to Democritus' deduction that matter ought to reduce to an invariant state, the Ptolemaic astronomy of a crystalline firmament, and Aristotle's book Physics, different Greek philosophers advanced their own theories of nature. Well into the 18th century, physics was known as natural philosophy.

By the 19th century physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on philosophy of science to give an adequate description of the scientific method.[15] The scientific method employs a priori reasoning as well as a posteriori reasoning and the use of Bayesian inference to measure the validity of a given theory.[16]

The development of physics has answered many questions of early philosophers, but has also raised new questions. Study of the philosophical issues surrounding physics, the philosophy of physics, involves issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism and realism.[17]

Many physicists have written about the philosophical implications of their work, for instance Laplace, who championed causal determinism,[18] and Erwin Schrödinger, who wrote on quantum mechanics.[19] The mathematical physicist Roger Penrose has been called a Platonist by Stephen Hawking,[20] a view Penrose discusses in his book, The Road to Reality.[21] Hawking refers to himself as an "unashamed reductionist" and takes issue with Penrose's views.[22]
Core theories
Further information: Branches of physics, Classical physics, Modern physics, Topic outline of physics

Though physics deals with a wide variety of systems, certain theories are used by all physicists. Each of these theories were experimentally tested numerous times and found correct as an approximation of nature (within a certain domain of validity). For instance, the theory of classical mechanics accurately describes the motion of objects, provided they are much larger than atoms and moving at much less than the speed of light. These theories continue to be areas of active research, and a remarkable aspect of classical mechanics known as chaos was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Isaac Newton (1642–1727).

These central theories are important tools for research into more specialized topics, and any physicist, regardless of his or her specialization, is expected to be literate in them. These include classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.
Fundamental physics
The basic domains of physics

While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well described. General relativity has not yet been unified with the other fundamental descriptions; several candidates theories of quantum gravity are being developed.
Relation to other fields
This parabola-shaped lava flow illustrates the application of Mathematics in Physics – in this case, Galileo's law of falling bodies.
Mathematics and Ontology are used in Physics. Physics is used in Chemistry and Cosmology.
Prerequisites

Mathematics is the language used for compact description of the order in nature, especially the laws of Physics. This was noted and advocated by Pythagoras,[23] Plato,[24] Galileo,[25] and Newton.

Physics theories use Mathematics[26] to obtain order and provide precise formulas, precise or estimated solutions, quantitative results and predictions. Experiment results in physics are numerical measurements. Technologies based on Mathematics, like computation have made computational physics an active area of research.
The distinction between Mathematics and Physics is clear-cut, but not always obvious, especially in Mathematical Physics.

Ontology is a prerequisite for Physics, but not for Mathematics. It means Physics ultimately concerned with descriptions of the real world, while Mathematics is concerned with abstract patterns, even beyond the real world. Thus Physics statements are synthetic, while Math statements are analytic. Mathematics contains hypothesis, while Physics contains theories. Mathematics statements have to be only logically true, while predictions of Physics statements must match observed and experimental data.

The distinction is clear-cut, but not always obvious. For example, Mathematical Physics is the application of Mathematics in Physics. Its methods are Mathematical, but its subject is Physical.[27] The problems in this field start with a "Math model of a Physical situation" and a "Math description of a Physical law". Every math statement used for solution has a hard-to-find Physical meaning. The final Mathematical solution has an easier-to-find meaning, because it is what the solver is looking for.

Physics is a branch of fundamental science, not practical science.[28] Physics is also called "the fundamental science" because the subject of study of all branches of natural science like Chemistry, Astronomy, Geology and Biology are constrained by laws of physics.[29] For example, Chemistry studies properties, structures, and reactions of matter (chemistry's focus on the atomic scale distinguishes it from physics). Structures are formed because particles exert electrical forces on each other, properties include physical characteristics of given substances, and reactions are bound by laws of physics, like conservation of energy, mass and charge.

Physics is applied in industries like engineering and medicine.
Application and influence
Archimedes' screw, a simple machine for lifting.
application in lifting liquids
Main article: Applied physics

Applied physics is a general term for physics research which is intended for a particular use. An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. It usually differs from engineering in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem.

The approach is similar to that of applied mathematics. Applied physicists can also be interested in the use of physics for scientific research. For instance, people working on accelerator physics might seek to build better particle detectors for research in theoretical physics.

Physics is used heavily in engineering. For example, Statics, a subfield of mechanics, is used in the building of bridges and other structures. The understanding and use of acoustics results in better concert halls; similarly, the use of optics creates better optical devices. An understanding of physics makes for more realistic flight simulators, video games, and movies, and is often critical in forensic investigations.

With the standard consensus that the laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in uncertainty. For example, in the study of the origin of the Earth, one can reasonably model Earth's mass, temperature, and rate of rotation, over time. It also allows for simulations in engineering which drastically speed up the development of a new technology.

But there is also considerable interdisciplinarity in the physicist's methods, and so many other important fields are influenced by physics: e.g. presently the fields of econophysics plays an important role, as well as sociophysics.
Research
Scientific method

Physicists use a scientific method to test the validity of a physical theory, using a methodical approach to compare the implications of the theory in question with the associated conclusions drawn from experiments and observations conducted to test it. Experiments and observations are to be collected and matched with the predictions and hypotheses made by a theory, thus aiding in the determination or the validity/invalidity of the theory.

Theories which are very well supported by data and have never failed any competent empirical test are often called scientific laws, or natural laws. Of course, all theories, including those called scientific laws, can always be replaced by more accurate, generalized statements if a disagreement of theory with observed data is ever found.[30]
Theory and experiment
Main articles: Theoretical physics and Experimental physics
The astronaut and Earth are both in free-fall
Lightning is an electric current

Theorists seek to develop mathematical models that both agree with existing experiments and successfully predict future results, while experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena. Although theory and experiment are developed separately, they are strongly dependent upon each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot explain, or when new theories generate experimentally testable predictions, which inspire new experiments.

Physicists who work at the interplay of theory and experiment are called phenomenologists. Phenomenologists look at the complex phenomena observed in experiment and work to relate them to fundamental theory.

Theoretical physics has historically taken inspiration from philosophy; electromagnetism was unified this way.[31] Beyond the known universe, the field of theoretical physics also deals with hypothetical issues,[32] such as parallel universes, a multiverse, and higher dimensions. Theorists invoke these ideas in hopes of solving particular problems with existing theories. They then explore the consequences of these ideas and work toward making testable predictions.

Experimental physics informs, and is informed by, engineering and technology. Experimental physicists involved in basic research design and perform experiments with equipment such as particle accelerators and lasers, whereas those involved in applied research often work in industry, developing technologies such as magnetic resonance imaging (MRI) and transistors. Feynman has noted that experimentalists may seek areas which are not well explored by theorists.[33]
Scope and aims
Physics involves modeling the natural world with theory, usually quantitative. Here, the path of a particle is modeled with the mathematics of calculus to explain its behavior: the purview of the branch of physics known as mechanics.

Physics covers a wide range of phenomena, from elementary particles (such as quarks, neutrinos and electrons) to the largest superclusters of galaxies. Included in these phenomena are the most basic objects composing all other things. Therefore physics is sometimes called the "fundamental science".[29] Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Thus, physics aims to both connect the things observable to humans to root causes, and then connect these causes together.

For example, the ancient Chinese observed that certain rocks (lodestone) were attracted to one another by some invisible force. This effect was later called magnetism, and was first rigorously studied in the 17th century. A little earlier than the Chinese, the ancient Greeks knew of other objects such as amber, that when rubbed with fur would cause a similar invisible attraction between the two. This was also first studied rigorously in the 17th century, and came to be called electricity. Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, further work in the 19th century revealed that these two forces were just two different aspects of one force – electromagnetism. This process of "unifying" forces continues today, and electromagnetism and the weak nuclear force are now considered to be two aspects of the electroweak interaction. Physics hopes to find an ultimate reason (Theory of Everything) for why nature is as it is (see section Current research below for more information).
Research fields

Contemporary research in physics can be broadly divided into condensed matter physics; atomic, molecular, and optical physics; particle physics; astrophysics; geophysics and biophysics. Some physics departments also support research in Physics education.

Since the twentieth century, the individual fields of physics have become increasingly specialized, and today most physicists work in a single field for their entire careers. "Universalists" such as Albert Einstein (1879–1955) and Lev Landau (1908–1968), who worked in multiple fields of physics, are now very rare.[34]
Table of the major fields of physics, along with their subfields and the theories they employ[show]
Field     Subfields     Major theories     Concepts
Astrophysics     Astronomy, Astrometry, Cosmology, Gravitation physics, High-energy astrophysics, Planetary astrophysics, Plasma physics, Solar Physics, Space physics, Stellar astrophysics     Big Bang, Cosmic inflation, General relativity, Newton's law of universal gravitation, Lambda-CDM model, Magnetohydrodynamics     Black hole, Cosmic background radiation, Cosmic string, Cosmos, Dark energy, Dark matter, Galaxy, Gravity, Gravitational radiation, Gravitational singularity, Planet, Solar system, Star, Supernova, Universe
Atomic, molecular, and optical physics     Atomic physics, Molecular physics, Atomic and Molecular astrophysics, Chemical physics, Optics, Photonics     Quantum optics, Quantum chemistry, Quantum information science     Photon, Atom, Molecule, Diffraction, Electromagnetic radiation, Laser, Polarization (waves), Spectral line, Casimir effect
Particle physics     Nuclear physics, Nuclear astrophysics, Particle astrophysics, Particle physics phenomenology     Standard Model, Quantum field theory, Quantum electrodynamics, Quantum chromodynamics, Electroweak theory, Effective field theory, Lattice field theory, Lattice gauge theory, Gauge theory, Supersymmetry, Grand unification theory, Superstring theory, M-theory     Fundamental force (gravitational, electromagnetic, weak, strong), Elementary particle, Spin, Antimatter, Spontaneous symmetry breaking, Neutrino oscillation, Seesaw mechanism, Brane, String, Quantum gravity, Theory of everything, Vacuum energy
Condensed matter physics     Solid state physics, High pressure physics, Low-temperature physics, Surface Physics, Nanoscale and Mesoscopic physics, Polymer physics     BCS theory, Bloch wave, Density functional theory, Fermi gas, Fermi liquid, Many-body theory, Statistical Mechanics     Phases (gas, liquid, solid), Bose-Einstein condensate, Electrical conduction, Phonon, Magnetism, Self-organization, Semiconductor, superconductor, superfluid, Spin,
Applied Physics     Accelerator physics, Acoustics, Agrophysics, Biophysics, Chemical Physics, Communication Physics, Econophysics, Engineering physics, Fluid dynamics, Geophysics, Laser Physics, Materials physics, Medical physics, Nanotechnology, Optics, Optoelectronics, Photonics, Photovoltaics, Physical chemistry, Physics of computation, Plasma physics, Solid-state devices, Quantum chemistry, Quantum electronics, Quantum information science, Vehicle dynamics
Condensed matter
Main article: Condensed matter physics

Velocity-distribution data of a gas of rubidium atoms, confirming the discovery of a new phase of matter, the Bose–Einstein condensate

Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. In particular, it is concerned with the "condensed" phases that appear whenever the number of constituents in a system is extremely large and the interactions between the constituents are strong.

The most familiar examples of condensed phases are solids and liquids, which arise from the bonding and electromagnetic force between atoms. More exotic condensed phases include the superfluid and the Bose–Einstein condensate found in certain atomic systems at very low temperature, the superconducting phase exhibited by conduction electrons in certain materials, and the ferromagnetic and antiferromagnetic phases of spins on atomic lattices.

Condensed matter physics is by far the largest field of contemporary physics. Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields. The term condensed matter physics was apparently coined by Philip Anderson when he renamed his research group — previously solid-state theory — in 1967.

In 1978, the Division of Solid State Physics at the American Physical Society was renamed as the Division of Condensed Matter Physics.[35] Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering.
Atomic, molecular, and optical physics
Main article: Atomic, molecular, and optical physics

Atomic, molecular, and optical physics (AMO) is the study of matter-matter and light-matter interactions on the scale of single atoms or structures containing a few atoms. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of the energy scales that are relevant. All three areas include both classical and quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view).

Atomic physics studies the electron shells of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics, the collective behavior of atoms in weakly interacting gases (Bose–Einstein Condensates and dilute Fermi degenerate systems), precision measurements of fundamental constants, and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the nucleus (see, e.g., hyperfine splitting), but intra-nuclear phenomenon such as fission and fusion are considered part of high energy physics.

Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light. Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects, but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.
High energy/particle physics
Main article: Particle physics

A simulated event in the CMS detector of the Large Hadron Collider, featuring a possible appearance of the Higgs boson.

Particle physics is the study of the elementary constituents of matter and energy, and the interactions between them. It may also be called "high energy physics", because many elementary particles do not occur naturally, but are created only during high energy collisions of other particles, as can be detected in particle accelerators.

Currently, the interactions of elementary particles are described by the Standard Model. The model accounts for the 12 known particles of matter (quarks and leptons) that interact via the strong, weak, and electromagnetic fundamental forces. Dynamics are described in terms of matter particles exchanging gauge bosons (gluons, W and Z bosons, and photons, respectively). The Standard Model also predicts a particle known as the Higgs boson, the existence of which has not yet been verified; as of 2010[update], searches for it are underway in the Tevatron at Fermilab and in the Large Hadron Collider at CERN.
Astrophysics
Main articles: Astrophysics and Physical cosmology

The deepest visible-light image of the universe, the Hubble Ultra Deep Field

Astrophysics and astronomy are the application of the theories and methods of physics to the study of stellar structure, stellar evolution, the origin of the solar system, and related problems of cosmology. Because astrophysics is a broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.

The discovery by Karl Jansky in 1931 that radio signals were emitted by celestial bodies initiated the science of radio astronomy. Most recently, the frontiers of astronomy have been expanded by space exploration. Perturbations and interference from the earth’s atmosphere make space-based observations necessary for infrared, ultraviolet, gamma-ray, and X-ray astronomy.

Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Albert Einstein’s theory of relativity plays a central role in all modern cosmological theories. In the early 20th century, Hubble's discovery that the universe was expanding, as shown by the Hubble diagram, prompted rival explanations known as the steady state universe and the Big Bang.

The Big Bang was confirmed by the success of Big Bang nucleosynthesis and the discovery of the cosmic microwave background in 1964. The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the cosmological principle. Cosmologists have recently established the ΛCDM model of the evolution of the universe, which includes cosmic inflation, dark energy and dark matter.

Numerous possibilities and discoveries are anticipated to emerge from new data from the Fermi Gamma-ray Space Telescope over the upcoming decade and vastly revise or clarify existing models of the Universe.[36][37] In particular, the potential for a tremendous discovery surrounding dark matter is possible over the next several years.[38] Fermi will search for evidence that dark matter is composed of weakly interacting massive particles, complementing similar experiments with the Large Hadron Collider and other underground detectors.

IBEX is already yielding new astrophysical discoveries: "No one knows what is creating the ENA (energetic neutral atoms) ribbon" along the termination shock of the solar wind, "but everyone agrees that it means the textbook picture of the heliosphere — in which the solar system's enveloping pocket filled with the solar wind's charged particles is plowing through the onrushing 'galactic wind' of the interstellar medium in the shape of a comet — is wrong."[39]
Current research
Further information: List of unsolved problems in physics
Feynman diagram signed by R. P. Feynman

A typical event described by physics: a magnet levitating above a superconductor demonstrates the Meissner effect.

Research in physics is continually progressing on a large number of fronts.

In condensed matter physics, an important unsolved theoretical problem is that of high-temperature superconductivity. Many condensed matter experiments are aiming to fabricate workable spintronics and quantum computers.

In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost among these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing solar neutrino problem, and the physics of massive neutrinos remains an area of active theoretical and experimental research. Particle accelerators have begun probing energy scales in the TeV range, in which experimentalists are hoping to find evidence for the Higgs boson and supersymmetric particles.[40]

Theoretical attempts to unify quantum mechanics and general relativity into a single theory of quantum gravity, a program ongoing for over half a century, have not yet been decisively resolved. The current leading candidates are M-theory, superstring theory and loop quantum gravity.

Many astronomical and cosmological phenomena have yet to be satisfactorily explained, including the existence of ultra-high energy cosmic rays, the baryon asymmetry, the acceleration of the universe and the anomalous rotation rates of galaxies.

Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena involving complexity, chaos, or turbulence are still poorly understood.[citation needed] Complex problems that seem like they could be solved by a clever application of dynamics and mechanics remain unsolved; examples include the formation of sandpiles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, and self-sorting in shaken heterogeneous collections.[citation needed]

These complex phenomena have received growing attention since the 1970s for several reasons, including the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. Complex physics has become part of increasingly interdisciplinary research, as exemplified by the study of turbulence in aerodynamics and the observation of pattern formation in biological systems. In 1932, Horace Lamb said:[41]

    I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.

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