化石(fossil)普遍在挖掘岩石的過程中被發現，其石化的物體，象徵著生命遺留的痕跡（化石一詞是源自拉丁語 fossilis）。有時候被石化的生物，還保存著原有的實際形體，如骨骼。有時候生物的遺骸，因被其周遭的岩石和礦物質滲入腐蝕，而成為岩石和礦物，其岩石仍保存著遺骸的形狀結構，所以化石可說是生物原有的遺骸和礦物化的遺骸，兩者之混合。也有化石形成的模式，像是用模型複印在石頭上，如脚印。最古老的化石是微化石 (microfossils)（藍綠藻 cyanobacteria 的化石），大約出現在34億5600萬年前。
連結網頁
- Some information about the very earliest fossils provided by Westphalia Wilhelms University in Münster. Most of the links from this site are dead, but some still work.
- A fine article by Peter N. Spotts in the Christian Science Monitor about the earliest fossils from 3.4 billion years ago.
- One of the many fine websites devoted to fossils.
- The San Diego Natural History Museum’s web page about finding fossils.
- William L. Newman’s old USGS publication Geologic Time has a page showing some index fossils used to date rocks.
- A good explanation of the concept of fossil succession.