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What is a fossil?
A fossil is any remnant, impression, or trace of an animal or plant from a past geologic age preserved in Earth’s crust. The fossil record is the primary source of information about the history of life on Earth.
Fossils are most often formed from organisms with solid, resistant skeletons. Hard parts like bones and teeth are more likely to be preserved than soft tissues, which tend to decompose rapidly. Rapid burial of the organism is also key to fossilization.
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How do fossils form?
Fossils usually form from organisms with solid skeletons. After death, rapid burial of the organism's hard parts, like bones and teeth, begins the slow fossilization process.
Burial allows minerals from the surrounding sediment to seep into the pores of the organism's hard parts. This mineral infusion can turn the organic material into stone, preserving the original shape and structure, or completely replace the original material, creating a stone replica. Soft tissues can fossilize, but this is rare; examples include insects in amber or mammoths in ice. The fossil record provides information about the history of life on Earth.
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What do paleontologists study using fossils?
Paleontologists analyze plant and animal fossils to study ancient life, including microscopic organisms preserved in rocks. They examine the shape, structure, evolutionary patterns, and relationships of these organisms with each other and with modern species. Fossils help determine the age of rock strata, offer insights into climate and environments, and document the evolution of animal groups. Hard parts of organisms, like bones and teeth, are more likely to fossilize, with minerals infusing or replacing the original material over time. Paleontological data has also aided petroleum geologists in locating oil and natural gas deposits.
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What types of fossils can be found?
Fossils are the remnants, impressions, or traces of past life preserved in Earth's crust. They provide key data about the history of life.
Fossils include:
* Fossils with unaltered hard parts Shells of clams are relatively common in sedimentary rocks.
* Permineralization Solutions fill the pores of the shell or bone with mineral salts.
* Mineralization or replacement Total replacement of the original skeletal material with mineral matter.
* Impressions Circulating solutions dissolve the original shell, leaving a cavity that creates an impression.
* Fossils of soft parts Rare examples include insects in amber and mammoths in ice.
* Microfossils Fossils of hard and soft parts too small to be seen with the naked eye.
* Trace fossils Evidence of an organism’s activities, such as tracks and trails.5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do scientists use fossils to learn about ancient environments?
Paleontologists use fossils to understand ancient environments by studying the remains of organisms to determine the conditions in which they lived. This involves analyzing whether the organism lived in the sea, lakes, or bogs, its biological community, food chain, and ecological niche.
Fossils can indicate past climates and environments of the site where they were deposited. For example, the presence of coral fossils suggests warm, shallow waters, while certain plant fossils indicate warm, swampy conditions. The study of spores and pollen can reveal successive climatic changes through the analysis of different vegetative complexes. This information helps to build a picture of what the Earth was like in the distant past.
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Why are fossil discoveries important for understanding the history of life on Earth?
Fossil discoveries are crucial to understanding the history of life on Earth because they serve as a record of the past. Fossils provide geologists a quick and easy way to assign an age to the strata in which they occur. The study of fossils helps describe the evolution of animal groups, and fossils can also provide information about the climate and environment of the site where they were deposited and preserved. The study of the distribution and succession of rock strata, as well as the character of the fossil organisms preserved within the strata, helps to determine the age and history of Earth’s rocks. Iconic dinosaur specimens, like those discovered by Mary Anning, frame a significant part of Earth’s geologic history and may have contributed to the theory of evolution. Fossils also serve as indicators of ancient environments.
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fossil, remnant, impression, or trace of an animal or plant of a past geologic age that has been preserved in Earth’s crust. The complex of data recorded in fossils worldwide—known as the fossil record—is the primary source of information about the history of life on Earth.
Only a small fraction of ancient organisms are preserved as fossils, and usually only organisms that have a solid and resistant skeleton are readily preserved. Most major groups of invertebrate animals have a calcareous skeleton or shell (e.g., corals, mollusks, brachiopods, bryozoans). Other forms have shells of calcium phosphate (which also occurs in the bones of vertebrates), or silicon dioxide. A shell or bone that is buried quickly after deposition may retain these organic tissues, though they become petrified (converted to a stony substance) over time. Unaltered hard parts, such as the shells of clams or brachiopods, are relatively common in sedimentary rocks, some of great age.
The hard parts of organisms that become buried in sediment may be subject to a variety of other changes during their conversion to solid rock, however. Solutions may fill the interstices, or pores, of the shell or bone with calcium carbonate or other mineral salts and thus fossilize the remains, in a process known as permineralization. In other cases there may be a total replacement of the original skeletal material by other mineral matter, a process known as mineralization, or replacement. In still other cases, circulating acid solutions may dissolve the original shell but leave a cavity corresponding to it, and circulating calcareous or siliceous solutions may then deposit a new matrix in the cavity, thus creating a new impression of the original shell.
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By contrast, the soft parts of animals or plants are very rarely preserved. The embedding of insects in amber (a process called resin fossilization) and the preservation of the carcasses of Pleistocene mammoths in ice are rare but striking examples of the fossil preservation of soft tissues. Leaves, stems, and other vegetable matter may be preserved through the process of carbonization, where such parts are flattened between two layers of rock. The chemical reduction of the part produces a carbon film that occurs on one layer of rock, while an impression of that part occurs on the other layer of the rock.
Fossils of hard and soft parts that are too small to be observed by the naked eye are called microfossils. Some fossils are completely devoid of plant and animal parts but show evidence of an organism’s activities. Such traces of organisms, which are appropriately known as “trace fossils,” include tracks or trails, preserved waste products, and borings.
The great majority of fossils are preserved in a water environment because land remains are more easily destroyed. Anaerobic conditions at the bottom of the seas or other bodies of water are especially favourable for preserving fine details, since no bottom faunas, except for anaerobic bacteria, are present to destroy the remains. In general, for an organism to be preserved two conditions must be met: rapid burial to retard decomposition and to prevent the ravaging of scavengers; and possession of hard parts capable of being fossilized.
In some places, such as the Grand Canyon in northern Arizona, one can observe a great thickness of nearly horizontal strata representing the deposition of sediment on the seafloor over many hundreds of millions of years. It is often apparent that each layer in such a sequence contains fossils that are distinct from those of the layers that are above and below it. In such sequences of layers in different geographic locations, the same, or similar, fossil floras or faunas occur in the identical order. By comparing overlapping sequences, it is possible to build up a continuous record of faunas and floras that have progressively more in common with present-day life forms as the top of the sequence is approached.
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The study of the fossil record has provided important information for at least four different purposes. The progressive changes observed within an animal group are used to describe the evolution of that group. Fossils also provide the geologist a quick and easy way of assigning a relative age to the strata in which they occur. The precision with which this may be done in any particular case depends on the nature and abundance of the fauna: some fossil groups were deposited during much longer time intervals than others. Fossils used to identify geologic relationships are known as index fossils.
Fossil organisms may provide information about the climate and environment of the site where they were deposited and preserved (e.g., certain species of coral require warm, shallow water, or certain forms of deciduous angiosperms can only grow in colder climatic conditions).
Fossils are useful in the exploration for minerals and mineral fuels. For example, they serve to indicate the stratigraphic position of coal seams. In recent years, geologists have been able to study the subsurface stratigraphy of oil and natural gas deposits by analyzing microfossils obtained from core samples of deep borings.
Fossil collection as performed by paleontologists, geologists, and other scientists typically involves a rigorous excavation and documentation process. Unearthing the specimen from the rock is often painstaking work that includes labeling each part of the specimen and cataloging the location of each part within the rock. Those fossils slated for removal from the rock are slowly and carefully excavated using techniques designed to prevent or minimize damage to the specimen. Such fossils often become part of museum or university collections.
Many other fossils, however, are collected by hobbyists and commercial entities. Often such specimens are not carefully documented or excavated, resulting in a loss of data from the site and risking potential damage to the specimen. For these reasons and the fact that it stimulates nonscientific collecting, the commercial exploitation of fossils is controversial among academic paleontologists.