Fossil

Graph showing the diversity of fossil species over geologic time

Fossil skeletons of Protoceratops and Psittacosaurus, often linked to the 'Griffin' myth

Fossil of Micraster coranguinum (sea urchin) from the Late Cretaceous

1812 sketch of the fossil skeleton of Anoplotherium, an extinct hoofed mammal

A fossil is the preserved remains, impression, or trace of once-living organisms from a past geological age. These remnants can be of animals, plants, fungi, or microorganisms, and are typically found embedded in sedimentary rock formations. The complete collection of fossils and their placement within rock layers is known as the fossil record, which provides critical evidence for the history of life on Earth.

Etymology

The term fossil originates from the Latin word fossilis, meaning "dug up." Initially, in the 16th century, it referred to anything unearthed from the ground, including minerals and artifacts. Over time, its usage narrowed to mean preserved remains of ancient life.

Formation

Fossilization is a rare and complex process that typically requires rapid burial and mineralization. The most common scenario involves an organism dying in a **watery environment**, where it becomes quickly buried under layers of mud or sand. Over thousands to millions of years, mineral-rich water infiltrates the remains, and the organic material may slowly be replaced by minerals, forming a fossil.

Common methods of fossil formation include:

• Permineralization – minerals deposit into the porous parts of the organism (e.g., bones, wood)
• Casts and molds – the organism leaves an impression that gets filled and preserved
• Carbonization – a carbon imprint remains after the organic material decays
• Amber preservation – organisms trapped in tree resin, which fossilizes into amber
• Freezing or desiccation – rare but results in well-preserved specimens

Types of Fossils

Fossils are generally categorized into two main types:

• Body fossils: These include the preserved physical remains of organisms such as bones, teeth, shells, leaves, and stems.
• Trace fossils: These represent the activity of organisms, such as footprints, burrows, coprolites (fossilized feces), and nesting sites.

Study of Fossils

The scientific study of fossils is known as paleontology. Paleontologists use fossils to:

• Reconstruct extinct organisms and ancient ecosystems
• Understand evolutionary relationships between species
• Date and correlate rock layers (stratigraphy)
• Study major extinction and radiation events in Earth's history

Importance

Fossils are vital for understanding the biological and geological history of Earth. They serve as:

• Direct evidence for the process of evolution and common descent
• Indicators of past climates and environments
• Tools for identifying and dating different geologic time periods

Fossils also guide petroleum geologists in locating fossil fuel deposits such as coal, oil, and natural gas.

Fossil Gallery

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  Early scientific illustration of Ichthyosaurus and Plesiosaurus fossils

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  Fossil of trilobite Eldredgeops rana crassituberculata

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  Stratigraphy at Montañita-Olón locality, part of the Dos Bocas Formation

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  Fossilized marine life within calcite minerals

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  Geodized fossil of Busycon snail with calcite crystals (Florida, USA)

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  Scleractinian coral fossils from the Matmor Formation (Middle Jurassic)

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  Silurian-period geodized pentamerid brachiopods (Indiana, USA)

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  Geopetal structure in a Carboniferous fossil, indicating original sediment orientation

See Also

• Paleontology
• Fossil record
• Fossil fuel
• Evolution
• Geologic time scale
• Stratigraphy
• Extinction event

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