Fathoming Geologic Time

OilIsMastery · Oct 23, 2008

The very earliest lifeforms of which we have record date back to nearly 3.8 billion years ago. These were procaryotes (a group that includes bacteria) consisting of little more than tiny bags of self-replicating chemicals, without so much as a localized nucleus. The oldest known eucaryotic cells (those with high-tech advances, including - most importantly - a membrane-bound nucleus) are single-celled organisms called protoctists (a group which includes amoebas, dinoflagellates and slime molds) dating back some 2.2 to 1.8 billion years. The Ediacaran assemblage in southern Australia is about 580 million years old and provides us with a look at the earliest-known multicellular life, a collection of bizarre invertebrates unlike anything alive today. Armored jawless fishes known as ostracoderms were the first true vertebrates, dating back to about 510 million years ago. Sharks appeared on the fossil scene about 455 to 425 million years ago. Those embodiments of prehistoric life, the dinosaurs, were relative late-comers - one of the earliest known genera (Herrerasaurus) dates back only about 230 million years.

The hominid fossil record goes back only about 4.5 million years, represented by a species called Ardipithicus ramidus from early Pliocene deposits in Ethiopia. These ape-like creatures could only be considered 'human' in the broadest, most generous sense of the word. Modern humans date back perhaps 60,000 years. Written language was developed only about 5,000 years ago. Therefore all of recorded human history - from the ancient Sumerians to you reading this sentence right now - represents a ridiculously tiny fraction (0.00013%) of the history of life on Earth.
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