古生代时期(Paleozoic) ，開始於前寒武紀 的生物爆發(大約5億4200萬年前)，到二叠紀末期的生物大滅絕(大約2億5100萬年前)，約有3億年之久。在古生代早期，大部分現存的生物門開始出現，在那時海底生物移居陸地。地球上目前許多自然資源的供給，如煤、石油和石灰岩，都是在古生代時期形成的。
連結網頁
- The National Atlas shows where you might find various sorts of Paleozoic rocks (for those living in North America)
- University of California Berkeley has a good site about the Paleozoic.
- Palaeos also has a very fine site about the Paleozoic, thanks to M. Alan Kazlev.
- If you want to know more about the Cambrian Explosion of life, learn about the Burgess Shale fossils at this site by Andrew MacRae of the University of Calgary.
- The International Commission on Stratigraphy has a good list of the ages making up the Paleozoic at this site.