Paleontology: Difference between revisions
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===A historical science=== |
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Paleontology is one of the "historical sciences", along with [[archaeology]], [[geology]], [[biology]], [[astronomy]], [[cosmogony]], [[philology]] and [[history]] itself.<ref name="Laudan1992WhatSpecial">{{ citation |
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| author=Laudan, R. | chapter=What's so Special about the Past? | page=p. 58 |
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| title=History and Evolution | editor=Nitecki, M.H., and Nitecki, D.V. | date=1992 |
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| publisher=SUNY Press | isbn=0791412113 |
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}}</ref> This means that it aims to describe phenomena of the past and reconstruct their causes.<ref name="Cleland2002MethodologicalAndEpistemicDifferences" /> Hence it has three main elements: description of the phenomena; developing a general theory about the causes of various types of change; and applying those theories ot specific facts.<ref name="Laudan1992WhatSpecial" /> |
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| ⚫ | When trying to trying to explain past phenomena, paleontologists and other historical scientists often construct a set of hypotheses about the causes and then look for a "[[smoking gun]]", a piece of evidence which indicates that one of the hypotheses is a better explanation than the others. Sometimes the "smoking gun" is discovered by a fortunate accident during other research, for example the discovery by [[Luis Alvarez]] and [[Walter Alvarez]] of an [[iridium]]-rich layer at the [[Cretaceous]]-[[Tertiary]] boundary made [[asteroid impact]] and [[volcanism]] the most favored explanations for the [[Cretaceous–Tertiary extinction event]]. |
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The other main type of science is experimental science, which is often said to work by conducting [[experiment]]s to ''disprove'' hypotheses about the workings and causes of natural phenomena – note that this approach cannot prove a hypothesis is correct, since some later experiment may disprove it. However when confronted with totally unexpected phenomena, such as the first evidence for [[ |
The other main type of science is experimental science, which is often said to work by conducting [[experiment]]s to ''disprove'' hypotheses about the workings and causes of natural phenomena – note that this approach cannot prove a hypothesis is correct, since some later experiment may disprove it. However when confronted with totally unexpected phenomena, such as the first evidence for invisible [[radiation]], experimental scientists often use the same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun".<ref name="Cleland2002MethodologicalAndEpistemicDifferences" /> |
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===Boundaries with other sciences=== |
===Boundaries with other sciences=== |
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Paleontology (british: palaeontology)[derivation 1] is the study of prehistoric life.
Life on Earth has a rich history spanning at least 3.5 billion years, although large organisms have only existed for about 600 million years. Life originated in the oceans and subsequently colonized the land, and was hit by a number of mass extinctions, at times wiping out as much as 95% of the biodiversity on Earth.
The more recent advent of humans does not typically fall under the remit of palaeontology: this is the realm of archaeology and anthropology. Organisms anatomically resembling modern humans have only existed for 2 million years, and advanced culture for 10,000 years - a much shorter timescale than studied by palaeontologists.
The remit of palaeontology also covers the search for traces of life on other worlds. For instance, it is very likely that life once existed on Mars, even if it doesn't today; thus palaeontology concerns itself with finding and identifying any traces it may have left.[1]
The evidence upon which palaeontologists base their conclusions is varied. Traditionally, it has centred on the (very incomplete) fossil record of organisms and the traces they left in sediments when they lived. However, modern analytical techniques have bolstered the available toolbox, and it is common to use biochemical, geochemical and genetic techniques to cast light on the affinity and behaviour of organims.
Definition
The simplest definition is "the study of ancient life"[2] Paleontology seeks information about several aspects of past organisms: "their identity and origin, their environment and evolution, and what they can tell us about the Earth's organic and inorganic past".[3]
A historical science
Paleontology is one of the "historical sciences", along with archaeology, geology, biology, astronomy, cosmogony, philology and history itself.[4] This means that it aims to describe phenomena of the past and reconstruct their causes.[5] Hence it has three main elements: description of the phenomena; developing a general theory about the causes of various types of change; and applying those theories ot specific facts.[4]
When trying to trying to explain past phenomena, paleontologists and other historical scientists often construct a set of hypotheses about the causes and then look for a "smoking gun", a piece of evidence which indicates that one of the hypotheses is a better explanation than the others. Sometimes the "smoking gun" is discovered by a fortunate accident during other research, for example the discovery by Luis Alvarez and Walter Alvarez of an iridium-rich layer at the Cretaceous-Tertiary boundary made asteroid impact and volcanism the most favored explanations for the Cretaceous–Tertiary extinction event. [5]
The other main type of science is experimental science, which is often said to work by conducting experiments to disprove hypotheses about the workings and causes of natural phenomena – note that this approach cannot prove a hypothesis is correct, since some later experiment may disprove it. However when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation, experimental scientists often use the same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun".[5]
Boundaries with other sciences
Background
Modern paleontology sets ancient life in its context by studying how long-term physical changes of global geography paleogeography and climate paleoclimate have affected the evolution of life, how ecosystems have responded to these changes and have adapted the planetary environment in turn and how these mutual responses have affected today's patterns of biodiversity. Hence, paleontology overlaps with geology (the study of rocks and rock formations) as well as with botany, biology, zoology and ecology – fields concerned with life forms and how they interact.
The major subdivisions of paleontology include paleozoology (animals), paleobotany (plants) and micropaleontology (microfossils). Paleozoologists may specialise in invertebrate paleontology, which deals with animals without backbones or in vertebrate paleontology, dealing with fossils of animals with backbones, including fossil hominids (paleoanthropology). Micropaleontologists study microscopic fossils, including organic-walled microfossils whose study is called palynology.
There are many developing specialties such as paleobiology, paleoecology, ichnology (the study of tracks and burrows) and taphonomy (the study of what happens to organisms after they expire). Major areas of study include the correlation of rock strata with their geologic ages and the study of evolution of lifeforms.
Paleontology utilises the same classic binomial nomenclature scheme, devised for the biology of living things by the mid-18th century Swedish biologist Carolus Linnaeus and increasingly sets these species in a genealogical framework, showing their degrees of interrelatedness using the still somewhat controversial technique of 'cladistics'.
The primary economic importance of paleontology lies in the use of fossils to determine the age and nature of the rocks that contain them or the layers above or below. This information is vital to the mining industry and especially the petroleum industry. Simply looking at the fossils contained in a rock remains one of the fastest and most accurate means of telling how old that rock is.
Fossils were known by primitive humans and were sometimes identified correctly as the remains of ancient lifeforms. The organized study of paleontology dates from the late 18th century. For a more complete historical overview see the article History of paleontology.
Overview of the history of life
Sources of evidence
Evidence of the history of life relies upon physical, biological and chemical signatures preserved in rocks.
One difficulty is deducing the age of rocks. Relative dating (A was before B) is often sufficient for studying processes of evolution, but this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents.[6]
An absolute age can be placed on rocks containing radiogenic minerals such as uranium, by radiometric dating.
Body fossils
Fossils of organisms' bodies are usually the most informative type of evidence. 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, they are often adequate to illustrate the broader patterns of life's history.[7] There are also biases in the fossil record: different environments are more favourable to the preservation of different types of organism or parts of organisms.[8] 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.[9]
Occasionally, unusual environments may preserve soft tissues. These allow palæontologists to examine the internal anatomy of animals which in other sediments are only represented by shells, spines, claws, etc – if they are preserved at all.
The sparseness of the fossil record means that organisms usually exist long before they are found in the fossil record - this is known as the Signor-Lipps effect.[10]
Trace fossils
Trace fossils consist mainly of tracks and burrows on and under what was then the seabed.
Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily-fossilized hard parts, and which reflects organisms' behaviour. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them.[11] Whilst exact assignment of trace fossils to their makers is generally impossible, traces may provide the earliest physical evidence of the appearance of moderately complex animals (comparable to earthworms).
Geochemical observations
Geochemical observations may help deduce the global level of biological activity, or the affinity of a certain fossil.
Phylogenetic techniques
Cladistics is a technique for working out the “family tree” of a set of organisms. It works by 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 which are compared may be anatomical, such as the presence of a notochord, or molecular, by comparing sequences of DNA or protein. The result of a successful analysis is a hierarchy of clades – groups whose members are believed to share a common ancestor. 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.
From the relationships, it may be possible to constrain the date that 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 acestor must have lived – by assuming that DNA mutations accumulate at a constant rate. These "molecular clocks", however, are fallible, and provide only a very approximate timing: they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved,[12] and estimates produced by different techniques vary by a factor of two.[13]
Genetics and Evo-devo
History of paleontology
See also
- Timeline of paleontology
- Important publications in paleontology
- Fossils
- History of paleontology
- Evolutionary history of life
- Geology
- Dinosaurs
- Radiometric dating
- Fossil collecting
- List of transitional fossils
- List of notable fossils
- List of fossil sites (with link directory)
References
- ^ from Greek: παλαιός (palaeos) "old, ancient", ὄν, ὀντ- (on, ont-) "being, creature", and λόγος (logos) "speech, thought"
- ^ . doi:10.1017/S1473550408004175.
{{cite journal}}: Cite journal requires|journal=(help); Missing or empty|title=(help) - ^ Cowen, R. History of Life (3rd ed.). Blackwell Science. ISBN 063204444-6.
- ^ Laporte, L.F. (October 1988). "What, after All, Is Paleontology?". Palaios. 3 (5): p. 453. Retrieved 2008-09-17.
{{cite journal}}:|page=has extra text (help) - ^ a b Laudan, R. (1992), "What's so Special about the Past?", in Nitecki, M.H., and Nitecki, D.V. (ed.), History and Evolution, SUNY Press, p. p. 58, ISBN 0791412113
{{citation}}:|page=has extra text (help)CS1 maint: multiple names: editors list (link) - ^ a b c Cleland, C.E. (September 2002). "Methodological and Epistemic Differences between Historical Science and Experimental Science". Philosophy of Science. 69: 474–496. Retrieved 2008-09-17.
- ^ e.g. Gehling, James; Jensen, Sören; Droser, Mary; Myrow, Paul; Narbonne, Guy (2001). "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine. 138 (2): 213–218. doi:10.1017/S001675680100509X.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Benton MJ, Wills MA, Hitchin R (2000). "Quality of the fossil record through time". Nature. 403 (6769): 534–7. doi:10.1038/35000558. PMID 10676959.
{{cite journal}}: CS1 maint: multiple names: authors list (link)- Non-technical summary
- ^ Butterfield , N.J. (2003). "Exceptional Fossil Preservation and the Cambrian Explosion". Integrative and Comparative Biology. 43 (1): 166–177. doi:10.1093/icb/43.1.166. Retrieved 2008-06-28.
- ^ Cowen, R. History of Life. Blackwell Science.
- ^ Signor, P.W. (1982). "Sampling bias, gradual extinction patterns and catastrophes in the fossil record". Geological implications of impacts of large asteroids and comets on the earth. Boulder, CO: Geological Society of America: 291–296. A 84–25651 10–42. Retrieved 2008-01-07.
- ^ e.g. Seilacher, A. (1994). "How valid is Cruziana Stratigraphy?" (PDF). International Journal of Earth Sciences. 83 (4): 752–758. Retrieved 2007-09-09.
- ^ Hug, L.A., and Roger, A.J. (2007). "The Impact of Fossils and Taxon Sampling on Ancient Molecular Dating Analyses". Molecular Biology and Evolution. 24 (8): 889–1897.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Peterson, Kevin J., and Butterfield, N.J. (2005). "Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record". Proceedings of the National Academy of Sciences. 102 (27): 9547. doi:10.1073/pnas.0503660102. PMID 15983372.
{{cite journal}}: CS1 maint: multiple names: authors list (link)
External links
- Smithsonian's Paleobiology website: a good introduction
- University of California Museum of Paleontology FAQ About Paleontology
- The Paleontological Society
- The Palaeontological Association
- The Paleontology Portal
- International Palaeoentomological Society
