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，如腳印。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。
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相關連結
1. 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.
2. A fine article by Peter N. Spotts in the Christian Science Monitor about the earliest fossils from 3.4 billion years ago.
3. One of the many fine websites devoted to fossils.
4. The San Diego Natural History Museum’s web page about finding fossils.
5. William L. Newman’s old USGS publication Geologic Time has a page showing some index fossils used to date rocks.
6. A good explanation of the concept of fossil succession.
