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Home Science Earth Science, Geologic Time & Fossils Fossils & Geologic Time
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FOSSIL

paleontology
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The Editors of Encyclopaedia Britannica
Last Updated: Dec 10, 2023 • Article History
Table of Contents
fossil
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Category: Animals & Nature
Key People: Charles Darwin Georges Cuvier Alfred Sherwood Romer George Gaylord
Simpson Mary Anning (Show more)
Related Topics: dinosaur Australopithecus Homo erectus Ardipithecus Neanderthal
(Show more)
See all related content →


RECENT NEWS

Dec. 9, 2023, 4:27 AM ET (The Guardian)
Prehistoric fast food: fossil reveals final meal of young tyrannosaur
Dec. 2, 2023, 12:49 AM ET (Earth.com)
Bird tracks discovered that predate the oldest birds by 60 ...
Nov. 29, 2023, 8:05 AM ET (Yahoo News)
Fossil discovered on Norfolk beach could be 100 million years old
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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.


Dinosaur fossils found in Alberta, Canada.

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.

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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.


Know about the fossil collection in the University of California Museum of
Paleontology, including the saber-toothed tiger
A discussion of California fossils—notably those of sabre-toothed tigers and the
Smilodon—in the University of California Museum of Paleontology's collection on
the Berkeley campus.(more)
See all videos for this article

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.

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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.



Fossilized leaf.
Track the discovery of dinosaurs from 7th-century griffin legends to Richard
Owen's coining of Dinosauria
Learn about the history of people discovering fossils and the coining of the
term dinosaur.(more)
See all videos for this article

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
Fossil of a dinosaur in the Lufengosaurus genus lying where it was unearthed in
Yunnan province, China.(more)
See samples of what is possibly soft tissue discovered in a Lufengosaurus fossil
from the Jurassic Period
Learn about what is believed to be the oldest soft tissue ever found, in a
dinosaur fossil dating to the Jurassic Period.(more)
See all videos for this article

Lufengosaurus
A cross section showing preserved collagen in a vascular canal of a rib of
Lufengosaurus, a 195-million-year-old dinosaur fossil from the Early Jurassic
Period.(more)

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.

The Editors of Encyclopaedia BritannicaThis article was most recently revised
and updated by Adam Augustyn.




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