Fossils are the preserved remains, impressions, or traces of organisms that lived in past geological periods, typically millions of years ago. They form through natural processes when organisms become buried in sediment, minerals, or other protective materials that prevent decomposition. The study of fossils, known as paleontology, provides direct physical evidence of life’s history on Earth and documents the existence of extinct species that no longer survive today.
Formation
Fossils form through several distinct mechanisms:
- Permineralization: Minerals from groundwater fill the pores of buried organisms, hardening them into rock.
- Replacement: Original material is chemically altered and substituted by minerals like silica or pyrite.
- Molds and Casts: An organism leaves an impression in sediment that hardens, or the impression fills with minerals to create a replica.
- Amber: Tree resin hardens around insects or other small animals, preserving them intact.
Key Examples
- Trilobites: Recognizable global fossils representing incredibly successful marine Arthropods that thrived for over 270 million years. See Trilobites: Enduring Success and Mysterious Extinction of Ancient Arthropods for details on their longevity and extinction dynamics.