AlegsaOnline.com

Fossil: remains, traces, and the science of ancient life

A fossil is the preserved remains or trace of an organism from the geological past. This article explains how fossils form, types, preservation, significance, and how scientists study them.

Author: Leandro Alegsa Creation date: November 13, 2022 Last updated: May 29, 2026

simple.wikipedia.org · CC BY-SA 3.0

A fossil is any preserved remnant or sign of a once-living organism from the geological past. Fossils can be the mineralized parts of bodies, imprints left in sediment, or indirect evidence such as tracks and burrows. They most commonly occur in sedimentary rock, where layers of mud, silt and sand bury biological material and protect it from immediate decay. The study of fossils helps reconstruct ancient environments, evolutionary relationships and the history of life on Earth.

How fossils form

Fossilization is not a single process but a set of pathways that can preserve different aspects of organisms. In many cases the original organic molecules are replaced by minerals over long periods: shells and bones may be mineralized or petrified, often with minerals such as calcium carbonate or silica. Other routes include molds and casts where the body leaves an impression that later hardens, or preservation in substances that inhibit decay—such as tree resin that becomes amber, which can trap delicate tissues and even small arthropods.

Common types and examples

Fossils appear in many forms. Body fossils are the preserved hard parts like bones, teeth and shells; bones of vertebrates and the shells of molluscs (including clams and snails) are typical examples. Trace fossils record activity—footprints, burrows, feeding marks and feces—and provide behavioral information. Exceptional deposits can preserve soft-bodied organisms such as those in the Ediacaran biota, while amber can entomb feathers, hair or insects. Substances like coal and oil are derived from large accumulations of ancient organic matter and are sometimes classed as fossil resources.

Preservation bias and what the record shows

Not all organisms have the same chance of becoming fossils. Hard parts made of durable materials fossilize far more readily than soft tissues; thus the fossil record is biased toward organisms with shells, bones, or woody tissue. Aquatic and sediment-buried environments are more likely to produce fossils than dry, erosive settings. This bias must be taken into account when interpreting past biodiversity or ecosystem structure.

History of fossil study and disciplines

People have recognized and collected fossils for millennia, but modern scientific study developed in the 18th and 19th centuries as geology and biology matured. The study of fossils by geologists and biologists is called paleontology, and when focused on ecological relationships it is often termed paleobiology. Museums and institutions dedicated to museums and natural history or earth science collections preserve and display many well-known examples, such as the fossilized remains of dinosaurs.

Importance and applications

Fossils are essential records for understanding evolution, ancient climates and past environments. They are used to correlate rock layers and date geological strata indirectly, and they inform biological classification and phylogeny. Fossils also have economic significance: deposits of coal, oil and certain mineral resources are tied to ancient biological productivity and burial. Careful study of fossils, including rare molecular remnants or traces of DNA, can sometimes reveal details of physiology and relationships otherwise invisible from bones or shells alone.

Ammonites ("Ammon horns") are among the best known and most popular fossils. Here a representative of the species Perisphinctes wartae from the Upper Jurassic of the Innerstebergland (southern Lower Saxony).

Historical

The discovery of marine organisms in rocks on the mainland attracted attention in ancient and medieval times from China to Europe, and they were correctly interpreted by several scholars (including Xenophanes, Eratosthenes, Leonardo da Vinci) as the remains of organisms or the remains of a former sea cover. On the other hand, the ancient Greek philosopher Aristotle and the scholastics based on his teachings regarded them as the whims of nature (lusus naturae).

The term fossil was first used in 1546 by Georgius Agricola in his work De natura fossilium. While, as Agricola did, all curiosities found "during excavation" were initially referred to indiscriminately as fossils, including minerals, artefacts, strangely shaped roots or concretions, in the course of time the meaning was narrowed to objects that testified to the existence of prehistoric life. The Frenchman Jean-Baptiste Lamarck made a significant contribution to this with the chapter Sur les fossiles in his comprehensive work on the systematics of invertebrates, which appeared in 1801. Common names for fossils were also petrefact and fossilization, and indeed in many cases fossils are formed by organic matter being replaced by mineral substance. Accordingly, the predecessor of modern paleontology was called petrefactology until well into the 19th century. As early as 1667, the Dane Nicolaus Steno was the first modern scholar to prove that fossils are not the vagaries of nature, but the remains of living beings from an earlier time.

Fossil teeth of the Eocene shark Otodus obliquus. Such teeth were long interpreted as tongue stones (glossopetrae), among other things, and were only correctly recognized in the 17th century. Since sharks form new teeth throughout their lives (revolver dentition), shark teeth are among the most common vertebrate finds, whereas the cartilaginous shark skeleton is only rarely preserved in fossils.

Noun fossil vs. adjective fossil

In addition to the term fossil as a noun, the word is also used as an adjective to characterize objects or formations that are geologically relatively old. In this sense, the adjective fossil is still used today not exclusively for the remains of living beings, for example in the word combination fossil energy sources (coal, oil, natural gas) or fossil water (very old deep groundwater). The opposite of the adjective fossil is recent. It refers to all formations that are relatively young geologically. Geological evidence whose age is on the borderline between fossil and recent can be called subfossil or subrecent. This concerns formations from the Quaternary period up to about 8000 BC (see also → Prehistory). In palaeobotany, however, subfossil also often refers to incomplete fossilization, i.e. a particular state of preservation. In this sense, even floras from the Palaeogene (older than 25 million years) can still be considered subfossil.

In biology and paleontology, the adjective fossil is also used to refer to extinct species. Fossil species" are those species that became extinct before the turn from the Pleistocene to the Holocene, i.e. more than about 12,000 years ago. Fossil species can be contrasted with recent species that became extinct only in the Holocene or that still exist today. The so-called living fossils are also (recent) species, not individual specimens. The totality of all fossil species currently known to science and their occurrence is called the fossil record.

In geomorphology, surface forms that still exist today but whose formation process came to a standstill in the geological past (so-called inactive structures) are referred to as fossil. This also applies to formations that are significantly younger than 10,000 years, for example inactive Holocene cliffs in landfall areas of the German Baltic Sea coast.

Questions and Answers

Q: What is a fossil?

A: A fossil is the remains or trace of an ancient living thing that has been mineralised or petrified (literally, turned into rock). It can be bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal and DNA remnants.

Q: How are fossils formed?

A: Fossils are formed when the body form of an ancient living thing is retained but the original molecules that made up the body have been replaced by some inorganic material such as calcium carbonate (CaCO3) or silica (SiO2).

Q: What type of organisms are most commonly found as fossils?

A: The most common fossils are those left behind by organisms that produce hard materials such as molluscs (clams and snails) and brachiopods (lampshells).

Q: Are there any examples of soft-bodied organisms being found as fossils?

A: Yes. Soft-bodied organisms can fossilise in special circumstances - for example the Ediacaran biota.

Q: What do people study when they look at fossils?

A: People who study fossils are known as paleontologists. If they put living things in their ecological context it is called paleobiology.

Q: Are there any famous examples of fossils?

A: Yes. The best-known fossils for the general public are those of giant prehistoric dinosaurs - their fossilized bones and tracks can be seen in many museums around the world.

Author

AlegsaOnline.com - Fossil - Leandro Alegsa

Creation date: November 13, 2022
Last updated: May 29, 2026

URL: https://en.alegsaonline.com/art/35834