Fossil

Jai Ganesh · 2025-10-24 21:48:59

Fossil

Gist

Fossils are the preserved remains of plants and animals whose bodies were buried in sediments, such as sand and mud, under ancient seas, lakes and rivers. Fossils also include any preserved trace of life that is typically more than 10 000 years old.

Fossils are the preserved remains or traces of once-living organisms, typically from more than 10,000 years ago, such as a dinosaur bone or an ammonite shell. They can include hard parts like bones and shells, or even evidence of an organism's activity, like footprints, and are formed through natural processes like being buried in sediment and mineralized over time.

Body fossils are the remains of past animals, plants, and microorganisms. Body fossils include bones, teeth, skin, shells, wood, and leaves. Molds, casts, steinkerns, and impressions are also body fossils since they result from marks made by the remains of organizations.

Summary

A fossil (from Classical Latin fossilis, lit. 'obtained by digging') is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record. Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of the pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of Tiktaalik in the arctic of Canada.

Paleontology includes the study of fossils: their age, method of formation, and evolutionary significance. Specimens are sometimes considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.

There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration.

Fossils vary in size from one-micrometre (1 μm) bacteria to dinosaurs and trees, many meters long and weighing many tons. The largest presently known is a Sequoia sp. measuring 88 m (289 ft) in length at Coaldale, Nevada. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils or ichnofossils, as opposed to body fossils. Some fossils are biochemical and are called chemofossils or biosignatures.

Details

A fossil is any 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.

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.

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.

Additional Information

Fossils are the preserved remains, or traces of remains, of ancient organisms.

A fossil can preserve an entire organism, just part, or traces of one (for example, footprints). Bones, shells, fur, skin, footprints, feathers and leaves can all become fossils.

Fossils can be very large or very small. The smallest fossils are called microfossils and are only visible with a microscope. Pollen fossils are microfossils. Fossils you can see with your eyes are called macrofossils and can be several meters long and weigh several tons. An example of a macrofossil could be a petrified tree or a dinosaur bone.

Preserved remains are defined as fossils if they are older than 10,000 years old. The oldest fossils are almost 4 billion years old and are traces of ocean-dwelling bacteria. Some of the youngest fossils (10 000 years old) are, for example, the fossilized teeth of woolly mammoths.

Fossilization

The word fossil comes from the Latin word fossus, meaning "having been dug up." Fossils are often found in rock formations, which although formed deep underground, have been moved to the surface (by plate tectonics) and/or been eroded to the Earth’s surface by wind, ice, rain and water.

Fossilization is the process of remains becoming fossils. Fossilization is rare. Most organisms decompose fairly quickly after they die.

For an organism to be fossilized, the remains usually need to be covered by sediment soon after death. Sediment can include the sandy or muddy seafloor, volcanic ash, and even sticky tar.

Over time, minerals in the sediment seep into the remains. The remains become fossilized. Fossilization more commonly occurs in organisms with hard, bony body parts, such as skeletons, teeth, or shells. Soft-bodied organisms, such as worms, are rarely fossilized, because soft parts quickly decompose or are eaten.

Sometimes, however, the sticky resin of a tree can become fossilized. This is called fossilized resin or amber. Amber can preserve the bodies of many delicate, soft-bodied organisms, such as ants, flies, and mosquitoes. While fossils found in rocks made of a soft sea floor are usually compressed, amber preserves the fossils in three dimensions.

Body Fossils and Trace Fossils

The fossils of bones, teeth, and shells are called body fossils. Most dinosaur fossils are collections of body fossils.

Trace fossils are rocks that have preserved evidence of biological activity. They are not fossilized remains, just the traces of organisms. The imprint of an ancient leaf or footprint is a trace fossil. Burrows can also create impressions in soft rocks or mud, leaving a trace fossil.

Paleontologists

Paleontologists are people who study fossils. Paleontologists find and study fossils all over the world, in almost every environment, from the hot desert to the humid jungle. Studying fossils helps them learn about when and how different species lived millions of years ago. Sometimes, fossils tell scientists how the Earth has changed. Fossils also help scientists study how species have evolved over the course of millions of years.

Fossils of ancient marine animals called ammonites have been unearthed in the highest mountain range in the world, the Himalayas in Nepal. This tells scientists that millions of years ago, the rocks that became the Himalayas were at the bottom of the ocean.

Fossils of an ancient giant shark, a megalodon (Carcharocles megalodon), have been found in the landlocked U.S. state of Utah. This tells scientists that millions of years ago, the middle of North America was probably entirely underwater when this animal lived.

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#1 2025-10-24 21:48:59

Fossil

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