How Is a Fossil Made?

fossil shells in rock

NPS photo/Jenny McGuire

Becoming a fossil is hard work. After an organism dies it must be buried deeply and rapidly to starve bacteria of the oxygen they need to digest the remains. Unfortunately, many animals die on the land surface and rot or are scavenged before they can be buried. Trampling by other animals or moving water can further degrade or break apart a skeleton. But if the remains are buried quickly, the process of fossilization can begin.
fossilized bone in rock with penny for scale

NPS photo/Scott Ireland

Groundwater rich with dissolved minerals, often silica or calcium carbonate, percolates through the pores in the rock, slowly replacing the organic compounds that make up the body of the animal. This process can take millions of years, but under the right circumstances, can preserve incredible details about the organism and its life.

Learn more about how dinosaur tracks are made

Return to the main Paleontology page

Last updated: June 13, 2015

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