How are fossils formed?

Fossils are created when the remains or impressions of plants and animals from previous geological eras are preserved in sedimentary rock . Fossilization typically begins when an organism with a solid skeleton dies, and its remains are quickly buried. The hard parts of the buried organism undergo transformation as minerals from the surrounding sediment seep into the pores of the bone or shell. This mineral infusion can turn the organic material into stone, preserving the shape and structure of the original organism. In some cases, the original material is completely replaced by minerals, creating a detailed stone replica. Soft tissues can fossilize, but this is rare.

What types of organisms are most likely to be found in the fossil record?

Organisms with solid and resistant skeletons are most likely to be found in the fossil record . Hard parts, such as bones, calcareous shells, or teeth, are more likely to be preserved than soft tissues, which tend to decompose rapidly. Most major groups of invertebrate animals have a calcareous skeleton or shell. Others have shells of calcium phosphate or silicon dioxide. Shells or bones that are buried quickly after deposition may retain these organic tissues, though they become petrified over time. The vast variety of organisms lacking hard parts are poorly represented in the geologic record; however, they sometimes occur as impressions or carbonized films in finely laminated sediments.

How do scientists use the fossil record to study Earth's history?

The fossil record is a crucial resource for scientists studying Earth's history. Fossils, which are the remains or imprints of organisms from earlier geologic periods, provide a wealth of information. By examining sequences of rock layers and the fossils they contain, scientists can observe progressive changes within animal groups, which helps describe the evolution of those groups. Fossils also help geologists assign ages to rock strata . Certain index fossils , easily recognizable and widely distributed, indicate particular time spans or environments. Furthermore, fossil organisms can offer insights into the climate and environment of the site where they were deposited, such as the presence of coral suggesting warm, shallow waters.

What can fossils tell us about past environments and extinct species?

The fossil record provides insights into the history of life on Earth, documenting organisms from earlier geological periods preserved as remains or imprints in sedimentary rock. Fossils reveal how animal groups have changed over time, often showing morphological adaptations to specific environments. Certain coral species, for example, indicate warm, shallow waters, while specific plants suggest warm, swampy conditions. Finding such fossils in polar regions implies that the Earth's crust has shifted since their deposition. Index fossils, those that are easily recognizable and widespread, help geologists assign ages to the rock strata in which they are found. The study of spores and pollen can further reveal ancient climates and vegetation complexes.

What are some limitations or gaps in the fossil record, and why do they exist?

The fossil record, while invaluable, has limitations. Preservation biases exist because organisms with hard parts are more likely to fossilize than soft-bodied ones. Additionally, the conditions for fossilization—rapid burial and anaerobic environments—are not universally present. Gaps in the record occur due to breaks in rock strata, affecting both the rock's composition and the fossils found within. Incomplete transitional records, combined with past knowledge gaps, have also contributed to the perception of abrupt appearances of fossils. Despite these limitations, the fossil record remains a primary source of information on the history of life on Earth.

fossil record

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Images & Videos

Dr. Jingmai O'Connor smiles and gestures toward a fossil of Archaeopteryx on display at the Field Museum, with exhibit text visible in the background.

Side-by-side illustration comparing a modern black-and-white bird on the left with a feathered dinosaur, Archaeopteryx, on the right, both with wings spread.

The video thumbnail image shows an illustration of the bird dinosaur Longipteryx alongside two toy dinosaur figurines.

Diagram comparing two columns of rock layers, labeled A and B, each containing distinct fossil illustrations at various depths. The matching fossils in corresponding layers show how geologists use fossils to determine the relative ages of rock layers, even when the sections are separated by 200 miles.

Map depicting the ancient supercontinent Gondwana, with colored bands showing the overlapping geographic home ranges of four prehistoric species-Cynognathus, Lystrosaurus, Glossopteris, and Mesosaurus-extending across present-day South America, Africa, India, Antarctica, and Australia.

A vertical geologic time scale chart spanning from 650 million years ago to the present, with colored bands for each era and period. Illustrations and labels highlight key evolutionary events such as the appearance of skeletal elements, first fishes, land plants, amphibians, reptiles, dinosaurs, mammals, and humans.

Quick Facts

Key People:: Charles Darwin; Per Teodor Cleve

Related Topics:: fossil; law of faunal succession; paleontology; index fossil; biostratigraphic unit

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Top Questions

What is the fossil record?
The fossil record documents the history of life using fossils, which are the remains or imprints of organisms from earlier geologic periods preserved in sedimentary rock. In some instances, the original substance of the hard parts of the organism is preserved, but more often the original components have been replaced by minerals. The study of the fossil record is used to describe the evolution of animal groups and to provide geologists a way to assign age to strata. Fossil organisms can also provide useful information about the climate and environment of the site where they were deposited and preserved.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are fossils formed?
Fossils are created when the remains or impressions of plants and animals from previous geological eras are preserved in sedimentary rock. Fossilization typically begins when an organism with a solid skeleton dies, and its remains are quickly buried.

The hard parts of the buried organism undergo transformation as minerals from the surrounding sediment seep into the pores of the bone or shell. This mineral infusion can turn the organic material into stone, preserving the shape and structure of the original organism. In some cases, the original material is completely replaced by minerals, creating a detailed stone replica. Soft tissues can fossilize, but this is rare.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What types of organisms are most likely to be found in the fossil record?
Organisms with solid and resistant skeletons are most likely to be found in the fossil record. Hard parts, such as bones, calcareous shells, or teeth, are more likely to be preserved than soft tissues, which tend to decompose rapidly.

Most major groups of invertebrate animals have a calcareous skeleton or shell. Others have shells of calcium phosphate or silicon dioxide. Shells or bones that are buried quickly after deposition may retain these organic tissues, though they become petrified over time.

The vast variety of organisms lacking hard parts are poorly represented in the geologic record; however, they sometimes occur as impressions or carbonized films in finely laminated sediments.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do scientists use the fossil record to study Earth's history?
The fossil record is a crucial resource for scientists studying Earth's history. Fossils, which are the remains or imprints of organisms from earlier geologic periods, provide a wealth of information. By examining sequences of rock layers and the fossils they contain, scientists can observe progressive changes within animal groups, which helps describe the evolution of those groups.

Fossils also help geologists assign ages to rock strata. Certain index fossils, easily recognizable and widely distributed, indicate particular time spans or environments. Furthermore, fossil organisms can offer insights into the climate and environment of the site where they were deposited, such as the presence of coral suggesting warm, shallow waters.
4 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What can fossils tell us about past environments and extinct species?
The fossil record provides insights into the history of life on Earth, documenting organisms from earlier geological periods preserved as remains or imprints in sedimentary rock.

Fossils reveal how animal groups have changed over time, often showing morphological adaptations to specific environments. Certain coral species, for example, indicate warm, shallow waters, while specific plants suggest warm, swampy conditions. Finding such fossils in polar regions implies that the Earth's crust has shifted since their deposition.

Index fossils, those that are easily recognizable and widespread, help geologists assign ages to the rock strata in which they are found. The study of spores and pollen can further reveal ancient climates and vegetation complexes.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some limitations or gaps in the fossil record, and why do they exist?
The fossil record, while invaluable, has limitations. Preservation biases exist because organisms with hard parts are more likely to fossilize than soft-bodied ones. Additionally, the conditions for fossilization—rapid burial and anaerobic environments—are not universally present.

Gaps in the record occur due to breaks in rock strata, affecting both the rock's composition and the fossils found within. Incomplete transitional records, combined with past knowledge gaps, have also contributed to the perception of abrupt appearances of fossils. Despite these limitations, the fossil record remains a primary source of information on the history of life on Earth.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

fossil record, history of life as documented by fossils, the remains or imprints of organisms from earlier geological periods preserved in sedimentary rock. In a few cases the original substance of the hard parts of the organism is preserved, but more often the original components have been replaced by minerals deposited from water seeping through the rock. Occasionally the original material is simply removed while nothing is deposited in its place; in this case, all that remains is a mould of the shape of the plant or animal. A brief treatment of the fossil record follows. For full treatment, see geochronology.

In some places, such as the Grand Canyon in Arizona, it is possible to recognize 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 observed 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 places, the same, or similar, fossil floras or faunas occur in the identical order. By comparison of overlapping sequences, it is possible to build up a continuous record of faunas or floras that have progressively more in common with present-day life-forms as the top of the sequence is approached.

Study of the fossil record has provided important information for at least three different purposes. The progressive changes observed within an animal group are used to describe the evolution of that group. In general, but not always, successive generations tend to change morphologically in a particular direction (e.g., the progressive acquisition or loss of specific features), and these changes are often interpreted as better adaptation (through preferential selection of beneficial mutations) to a particular environment.

Cross section of Earth showing the core, mantle, and crust

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Fossils also provide the geologist a quick and easy way of assigning an 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.

Fossil organisms, furthermore, may provide useful information about the climate and environment of the site where they were deposited and preserved. Certain species of coral, for example, require warm shallow water; certain plants require warm swampy conditions such as are found today in the Florida Everglades, South America’s Pantanal, and Botswana’s Okavango delta. Thus, when rocks containing fossils of this kind are found in rocks of the present-day polar regions, there is a strong presumption that the crust on which they were deposited has shifted its position on the surface of Earth since that time.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Meg Matthias.

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