Geologic Timescale By zedenstrom Feb 10, 1926 Cambrian Period- 570-500 MYA Triolobites were dominent. All lilfe was marine and many large multicellular organisms existed. Earth was mostly oceans. Feb 10, 1937 Ordivician Period-500-435 fnmrklea;r njhvoiea;vf djk;vn kfld.a hjviofd;eamfvdezsv