What is a Fossil

The fossils are the petrified remains of organisms that lived in ancient times.

Fossils are generally found in sedimentary rocks. For a fossil to form, the organism must go through a physical-chemical process called fossilization. This process petrifies the organism after it is buried and preserves it for a long time in the earth’s crust.


The importance of fossil finds and their study is that they serve to reconstruct the natural history of the world, collecting data and clues from organisms that existed in remote times, such as the discovery of dinosaur fossils.

Fossil can also be used in a colloquial sense to refer to something that is considered old, outdated, or obsolete.

In Mexico, students who lag behind their classmates in initial courses, or who have spent many years studying without really advancing, are colloquially called fossils.

In the past, fossil could also refer to minerals or rocks of any kind.

The science dedicated to the study of fossils is paleontology, from which subdisciplines such as:

  • paleobiology: that is in charge of the study of the organisms of the past;
  • biochronology: that analyzes and determines the period in which these organisms lived and
  • taphonomy: dealing with fossilization processes.

Fossils also help in the study of geology and evolutionary biology.

The word fossil comes from the Latin fossiliswhich in turn derives from the verb foderewhich means ‘to dig’.

types of fossils

The different types of fossils are classified by the period to which they belong and the type of fossilized organisms. In this sense, the most common fossils are those remains of ammonoids, species of mollusks, which lived between the Devonian and Cretaceous times some 330 million years ago.

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The most common fossil formation is through carbonization.

See also Carbonization.

living fossil

As a living fossil is known any organism currently alive that bears great resemblance to species from remote times, of which only knowledge is known through fossil records.

An example of this is the brachiopods, of which there is news from the lower Calambrian, that is, approximately 540 million years ago. There is also the coelacanth, a fish that lives off the coast of Africa and was thought extinct millions of years ago.

guide fossil

A guide fossil (also called director, index or characteristic) is called that fossil whose presence in an excavation allows determining with a certain level of precision the period to which the stratigraphic unit where it is found belongs, either because it is particular to a certain period of history geological, or because it is typical of a certain paleoenvironment.

See also:

  • Paleontology
  • geology