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75-572: The Knox Dolomite is a geologic formation in Mississippi and Ohio . It dates back to the Cambrian . This article about a specific stratigraphic formation in Ohio is a stub . You can help Misplaced Pages by expanding it . Formation (geology) A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by

150-471: A jigsaw puzzle . Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age must lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion , it is very difficult to match up rock beds that are not directly next to one another. However, fossils of species that survived for

225-552: A collision that formed the Moon about 40 million years later, may have cooled quickly enough to have oceans and an atmosphere about 4,440  million years ago . There is evidence on the Moon of a Late Heavy Bombardment by asteroids from 4,000 to 3,800 million years ago . If, as seems likely, such a bombardment struck Earth at the same time, the first atmosphere and oceans may have been stripped away. Paleontology traces

300-602: A common ancestor. Ideally the "family tree" has only two branches leading from each node ("junction"), but sometimes there is too little information to achieve this, and paleontologists have to make do with junctions that have several branches. The cladistic technique is sometimes fallible, as some features, such as wings or camera eyes , evolved more than once, convergently  – this must be taken into account in analyses. Evolutionary developmental biology , commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees", and understand fossils. For example,

375-401: A constant rate. These " molecular clocks ", however, are fallible, and provide only a very approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Earth formed about 4,570  million years ago and, after

450-403: A data source that is not limited to animals with easily fossilised hard parts, and they reflect organisms' behaviours. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of

525-573: A fortunate accident during other research. For example, the 1980 discovery by Luis and Walter Alvarez of iridium , a mainly extraterrestrial metal, in the Cretaceous – Paleogene boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event – although debate continues about the contribution of volcanism. A complementary approach to developing scientific knowledge, experimental science ,

600-821: A minor group until the first jawed fish appeared in the Late Ordovician . The spread of animals and plants from water to land required organisms to solve several problems, including protection against drying out and supporting themselves against gravity . The earliest evidence of land plants and land invertebrates date back to about 476  million years ago and 490  million years ago respectively. Those invertebrates, as indicated by their trace and body fossils, were shown to be arthropods known as euthycarcinoids . The lineage that produced land vertebrates evolved later but very rapidly between 370  million years ago and 360  million years ago ; recent discoveries have overturned earlier ideas about

675-542: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

750-617: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

825-555: A rapid increase in knowledge about the history of life on Earth and to progress in the definition of the geologic time scale , largely based on fossil evidence. Although she was rarely recognised by the scientific community, Mary Anning was a significant contributor to the field of palaeontology during this period; she uncovered multiple novel Mesozoic reptile fossils and deducted that what were then known as bezoar stones are in fact fossilised faeces . In 1822 Henri Marie Ducrotay de Blainville , editor of Journal de Physique , coined

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900-543: A relatively short time can be used to link up isolated rocks: this technique is called biostratigraphy . For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age are found to have traces of E. pseudoplanus , they must have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and have a short time range to be useful. However, misleading results are produced if

975-608: A steady increase in brain size after about 3  million years ago . There is a long-running debate about whether modern humans are descendants of a single small population in Africa , which then migrated all over the world less than 200,000 years ago and replaced previous hominine species, or arose worldwide at the same time as a result of interbreeding . Life on earth has suffered occasional mass extinctions at least since 542  million years ago . Despite their disastrous effects, mass extinctions have sometimes accelerated

1050-449: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

1125-525: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Paleontology Paleontology ( / ˌ p eɪ l i ɒ n ˈ t ɒ l ə dʒ i , ˌ p æ l i -, - ən -/ PAY -lee-on- TOL -ə-jee, PAL -ee-, -⁠ən- ), also spelled palaeontology or palæontology ,

1200-560: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

1275-595: Is composed only of eukaryotic cells, and the earliest evidence for it is the Francevillian Group Fossils from 2,100  million years ago , although specialisation of cells for different functions first appears between 1,430  million years ago (a possible fungus) and 1,200  million years ago (a probable red alga ). Sexual reproduction may be a prerequisite for specialisation of cells, as an asexual multicellular organism might be at risk of being taken over by rogue cells that retain

1350-482: Is hard to decide at what level to place a new higher-level grouping, e.g. genus or family or order ; this is important since the Linnaean rules for naming groups are tied to their levels, and hence if a group is moved to a different level it must be renamed. Paleontologists generally use approaches based on cladistics , a technique for working out the evolutionary "family tree" of a set of organisms. It works by

1425-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

1500-443: Is often said to work by conducting experiments to disprove hypotheses about the workings and causes of natural phenomena. This approach cannot prove a hypothesis, since some later experiment may disprove it, but the accumulation of failures to disprove is often compelling evidence in favor. However, when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation , experimental scientists often use

1575-594: Is one that contained an extinct "crocodile-like" marine reptile, which eventually came to be known as the mosasaurid Mosasaurus of the Cretaceous period. The first half of the 19th century saw geological and paleontological activity become increasingly well organised with the growth of geologic societies and museums and an increasing number of professional geologists and fossil specialists. Interest increased for reasons that were not purely scientific, as geology and paleontology helped industrialists to find and exploit natural resources such as coal. This contributed to

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1650-401: Is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Although radiometric dating requires very careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to the element into which it decays shows how long ago

1725-456: Is the scientific study of life that existed prior to the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossils to classify organisms and study their interactions with each other and their environments (their paleoecology ). Paleontological observations have been documented as far back as the 5th century BC. The science became established in

1800-503: Is thought to have been propelled by coevolution with pollinating insects. Social insects appeared around the same time and, although they account for only small parts of the insect "family tree", now form over 50% of the total mass of all insects. Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over 6  million years ago . Although early members of this lineage had chimp -sized brains, about 25% as big as modern humans', there are signs of

1875-582: The Middle Ages the Persian naturalist Ibn Sina , known as Avicenna in Europe, discussed fossils and proposed a theory of petrifying fluids on which Albert of Saxony elaborated in the 14th century. The Chinese naturalist Shen Kuo (1031–1095) proposed a theory of climate change based on the presence of petrified bamboo in regions that in his time were too dry for bamboo. In early modern Europe ,

1950-538: The Neogene - Quaternary . In deeper-level deposits in western Europe are early-aged mammals such as the palaeothere perissodactyl Palaeotherium and the anoplotheriid artiodactyl Anoplotherium , both of which were described earliest after the former two genera, which today are known to date to the Paleogene period. Cuvier figured out that even older than the two levels of deposits with extinct large mammals

2025-637: The Permian–Triassic extinction event . Amphibians Extinct Synapsids Mammals Extinct reptiles Lizards and snakes Extinct Archosaurs Crocodilians Extinct Dinosaurs Birds Naming groups of organisms in a way that is clear and widely agreed is important, as some disputes in paleontology have been based just on misunderstandings over names. Linnaean taxonomy is commonly used for classifying living organisms, but runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. For example: it

2100-516: The Permian–Triassic extinction event . A relatively recent discipline, molecular phylogenetics , compares the DNA and RNA of modern organisms to re-construct the "family trees" of their evolutionary ancestors. It has also been used to estimate the dates of important evolutionary developments, although this approach is controversial because of doubts about the reliability of the " molecular clock ". Techniques from engineering have been used to analyse how

2175-454: The embryological development of some modern brachiopods suggests that brachiopods may be descendants of the halkieriids , which became extinct in the Cambrian period. Paleontology seeks to map out how living things have changed through time. A substantial hurdle to this aim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating . This technique

2250-439: The thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of a geologic formation goes back to the beginnings of modern scientific geology. The term

2325-526: The " jigsaw puzzles " of biostratigraphy (arrangement of rock layers from youngest to oldest). Classifying ancient organisms is also difficult, as many do not fit well into the Linnaean taxonomy classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics , which investigates how closely organisms are related by measuring

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2400-463: The 18th century as a result of Georges Cuvier 's work on comparative anatomy , and developed rapidly in the 19th century. The term has been used since 1822 formed from Greek παλαιός ( 'palaios' , "old, ancient"), ὄν ( 'on' , ( gen. 'ontos' ), "being, creature"), and λόγος ( 'logos' , "speech, thought, study"). Paleontology lies on the border between biology and geology , but it differs from archaeology in that it excludes

2475-555: The Early Cambrian , along with several "weird wonders" that bear little obvious resemblance to any modern animals. There is a long-running debate about whether this Cambrian explosion was truly a very rapid period of evolutionary experimentation; alternative views are that modern-looking animals began evolving earlier but fossils of their precursors have not yet been found, or that the "weird wonders" are evolutionary "aunts" and "cousins" of modern groups. Vertebrates remained

2550-463: The Earth's organic and inorganic past". William Whewell (1794–1866) classified paleontology as one of the historical sciences, along with archaeology , geology, astronomy , cosmology , philology and history itself: paleontology aims to describe phenomena of the past and to reconstruct their causes. Hence it has three main elements: description of past phenomena; developing a general theory about

2625-412: The ability to reproduce. The earliest known animals are cnidarians from about 580  million years ago , but these are so modern-looking that they must be descendants of earlier animals. Early fossils of animals are rare because they had not developed mineralised , easily fossilized hard parts until about 548  million years ago . The earliest modern-looking bilaterian animals appear in

2700-515: The appearance of moderately complex animals (comparable to earthworms ). Geochemical observations may help to deduce the global level of biological activity at a certain period, or the affinity of certain fossils. For example, geochemical features of rocks may reveal when life first arose on Earth, and may provide evidence of the presence of eukaryotic cells, the type from which all multicellular organisms are built. Analyses of carbon isotope ratios may help to explain major transitions such as

2775-625: The atmosphere increased their effectiveness as nurseries of evolution. While eukaryotes , cells with complex internal structures, may have been present earlier, their evolution speeded up when they acquired the ability to transform oxygen from a poison to a powerful source of metabolic energy. This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as endosymbionts and transforming them into organelles called mitochondria . The earliest evidence of complex eukaryotes with organelles (such as mitochondria) dates from 1,850  million years ago . Multicellular life

2850-415: The bodies of ancient organisms might have worked, for example the running speed and bite strength of Tyrannosaurus , or the flight mechanics of Microraptor . It is relatively commonplace to study the internal details of fossils using X-ray microtomography . Paleontology, biology, archaeology, and paleoneurobiology combine to study endocranial casts (endocasts) of species related to humans to clarify

2925-401: The causes of various types of change; and applying those theories to specific facts. When trying to explain the past, paleontologists and other historical scientists often construct a set of one or more hypotheses about the causes and then look for a " smoking gun ", a piece of evidence that strongly accords with one hypothesis over any others. Sometimes researchers discover a "smoking gun" by

3000-763: The characteristics and evolution of humans as a species. When dealing with evidence about humans, archaeologists and paleontologists may work together – for example paleontologists might identify animal or plant fossils around an archaeological site , to discover the people who lived there, and what they ate; or they might analyze the climate at the time of habitation. In addition, paleontology often borrows techniques from other sciences, including biology, osteology , ecology, chemistry , physics and mathematics. For example, geochemical signatures from rocks may help to discover when life first arose on Earth, and analyses of carbon isotope ratios may help to identify climate changes and even to explain major transitions such as

3075-520: The chronological order in which rocks were formed, is useful to both paleontologists and geologists. Biogeography studies the spatial distribution of organisms, and is also linked to geology, which explains how Earth's geography has changed over time. Although paleontology became established around 1800, earlier thinkers had noticed aspects of the fossil record. The ancient Greek philosopher Xenophanes (570–480 BCE) concluded from fossil sea shells that some areas of land were once under water. During

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3150-445: The date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved more than X million years ago. It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at

3225-594: The development of mammalian traits such as endothermy and hair. After the Cretaceous–Paleogene extinction event 66  million years ago killed off all the dinosaurs except the birds, mammals increased rapidly in size and diversity, and some took to the air and the sea. Fossil evidence indicates that flowering plants appeared and rapidly diversified in the Early Cretaceous between 130  million years ago and 90  million years ago . Their rapid rise to dominance of terrestrial ecosystems

3300-561: The development of the body plans of most animal phyla . The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian. Increasing awareness of Gregor Mendel 's pioneering work in genetics led first to the development of population genetics and then in the mid-20th century to the modern evolutionary synthesis , which explains evolution as

3375-482: The different levels of deposits represented different time periods in the early 19th century. The surface-level deposits in the Americas contained later mammals like the megatheriid ground sloth Megatherium and the mammutid proboscidean Mammut (later known informally as a "mastodon"), which were some of the earliest-named fossil mammal genera with official taxonomic authorities. They today are known to date to

3450-409: The end of the 20th century have been particularly important as they have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds. The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth. There was also a renewed interest in the Cambrian explosion that apparently saw

3525-550: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

3600-410: The evolution of the human brain. Paleontology even contributes to astrobiology , the investigation of possible life on other planets , by developing models of how life may have arisen and by providing techniques for detecting evidence of life. As knowledge has increased, paleontology has developed specialised subdivisions. Vertebrate paleontology concentrates on fossils from the earliest fish to

3675-466: The evolutionary history of life back to over 3,000  million years ago , possibly as far as 3,800  million years ago . The oldest clear evidence of life on Earth dates to 3,000  million years ago , although there have been reports, often disputed, of fossil bacteria from 3,400  million years ago and of geochemical evidence for the presence of life 3,800  million years ago . Some scientists have proposed that life on Earth

3750-555: The exceptional events that cause quick burial make it difficult to study the normal environments of the animals. The sparseness of the fossil record means that organisms are expected to exist long before and after they are found in the fossil record – this is known as the Signor–Lipps effect . Trace fossils consist mainly of tracks and burrows, but also include coprolites (fossil feces ) and marks left by feeding. Trace fossils are particularly significant because they represent

3825-515: The focus of paleontology shifted to understanding evolutionary paths, including human evolution , and evolutionary theory. The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection. Fossils found in China near

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3900-449: The following: At the end of the 18th century Georges Cuvier 's work established comparative anatomy as a scientific discipline and, by proving that some fossil animals resembled no living ones, demonstrated that animals could become extinct , leading to the emergence of paleontology. The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly stratigraphy . Cuvier proved that

3975-522: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

4050-580: The fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms. Further, only the parts of organisms that were already mineralised are usually preserved, such as the shells of molluscs. Since most animal species are soft-bodied, they decay before they can become fossilised. As a result, although there are 30-plus phyla of living animals, two-thirds have never been found as fossils. Occasionally, unusual environments may preserve soft tissues. These lagerstätten allow paleontologists to examine

4125-687: The history and driving forces behind their evolution. Land plants were so successful that their detritus caused an ecological crisis in the Late Devonian , until the evolution of fungi that could digest dead wood. During the Permian period, synapsids , including the ancestors of mammals , may have dominated land environments, but this ended with the Permian–Triassic extinction event 251  million years ago , which came very close to wiping out all complex life. The extinctions were apparently fairly sudden, at least among vertebrates. During

4200-533: The history of Earth's climate and the mechanisms that have changed it  – which have sometimes included evolutionary developments, for example the rapid expansion of land plants in the Devonian period removed more carbon dioxide from the atmosphere, reducing the greenhouse effect and thus helping to cause an ice age in the Carboniferous period. Biostratigraphy , the use of fossils to work out

4275-542: The immediate ancestors of modern mammals . Invertebrate paleontology deals with fossils such as molluscs , arthropods , annelid worms and echinoderms . Paleobotany studies fossil plants , algae , and fungi. Palynology , the study of pollen and spores produced by land plants and protists , straddles paleontology and botany , as it deals with both living and fossil organisms. Micropaleontology deals with microscopic fossil organisms of all kinds. Instead of focusing on individual organisms, paleoecology examines

4350-434: The index fossils turn out to have longer fossil ranges than first thought. Stratigraphy and biostratigraphy can in general provide only relative dating ( A was before B ), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents . Family-tree relationships may also help to narrow down

4425-538: The interactions between different ancient organisms, such as their food chains , and the two-way interactions with their environments.   For example, the development of oxygenic photosynthesis by bacteria caused the oxygenation of the atmosphere and hugely increased the productivity and diversity of ecosystems . Together, these led to the evolution of complex eukaryotic cells, from which all multicellular organisms are built. Paleoclimatology , although sometimes treated as part of paleoecology, focuses more on

4500-463: The internal anatomy of animals that in other sediments are represented only by shells, spines, claws, etc. – if they are preserved at all. However, even lagerstätten present an incomplete picture of life at the time. The majority of organisms living at the time are probably not represented because lagerstätten are restricted to a narrow range of environments, e.g. where soft-bodied organisms can be preserved very quickly by events such as mudslides; and

4575-456: The investigation of evolutionary "family trees" by techniques derived from biochemistry , began to make an impact, particularly when it was proposed that the human lineage had diverged from apes much more recently than was generally thought at the time. Although this early study compared proteins from apes and humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA . Fossils of organisms' bodies are usually

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4650-409: The logic that, if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characters that are compared may be anatomical , such as the presence of a notochord , or molecular , by comparing sequences of DNA or proteins . The result of a successful analysis is a hierarchy of clades – groups that share

4725-409: The most informative type of evidence. The most common types are wood, bones, and shells. Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time. Despite this, it is often adequate to illustrate the broader patterns of life's history. There are also biases in

4800-414: The outcome of events such as mutations and horizontal gene transfer , which provide genetic variation , with genetic drift and natural selection driving changes in this variation over time. Within the next few years the role and operation of DNA in genetic inheritance were discovered, leading to what is now known as the "Central Dogma" of molecular biology . In the 1960s molecular phylogenetics ,

4875-452: The principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating , which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving

4950-432: The radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers. Consequently, paleontologists must usually rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record, and has been compared to

5025-701: The same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun". Paleontology lies between biology and geology since it focuses on the record of past life, but its main source of evidence is fossils in rocks. For historical reasons, paleontology is part of the geology department at many universities: in the 19th and early 20th centuries, geology departments found fossil evidence important for dating rocks, while biology departments showed little interest. Paleontology also has some overlap with archaeology , which primarily works with objects made by humans and with human remains, while paleontologists are interested in

5100-478: The similarity of the DNA in their genomes . Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend. The simplest definition of "paleontology" is "the study of ancient life". The field seeks information about several aspects of past organisms: "their identity and origin, their environment and evolution, and what they can tell us about

5175-470: The slow recovery from this catastrophe a previously obscure group, archosaurs , became the most abundant and diverse terrestrial vertebrates. One archosaur group, the dinosaurs, were the dominant land vertebrates for the rest of the Mesozoic , and birds evolved from one group of dinosaurs. During this time mammals' ancestors survived only as small, mainly nocturnal insectivores , which may have accelerated

5250-631: The study of anatomically modern humans . It now uses techniques drawn from a wide range of sciences, including biochemistry , mathematics , and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life , almost back to when Earth became capable of supporting life, nearly 4 billion years ago. As knowledge has increased, paleontology has developed specialised sub-divisions, some of which focus on different types of fossil organisms while others study ecology and environmental history, such as ancient climates . Body fossils and trace fossils are

5325-629: The systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason . In the Italian Renaissance, Leonardo da Vinci made various significant contributions to the field as well as depicted numerous fossils. Leonardo's contributions are central to the history of paleontology because he established a line of continuity between the two main branches of paleontology – ichnology and body fossil paleontology. He identified

5400-546: The tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

5475-406: The word "palaeontology" to refer to the study of ancient living organisms through fossils. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This encouraged early evolutionary theories on the transmutation of species . After Charles Darwin published Origin of Species in 1859, much of

5550-454: Was "seeded" from elsewhere , but most research concentrates on various explanations of how life could have arisen independently on Earth. For about 2,000 million years microbial mats , multi-layered colonies of different bacteria, were the dominant life on Earth. The evolution of oxygenic photosynthesis enabled them to play the major role in the oxygenation of the atmosphere from about 2,400  million years ago . This change in

5625-568: Was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at the surface are fundamental to such fields as structural geology , allowing geologists to infer

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