Life has existed on the Earth for more than three billion years. Until the Cambrian explosion about 540 million years ago however, it was restricted mostly to single-celled micro-organisms that were, for the most part, poorly preserved in the fossil record. From the Cambrian explosion onwards, by contrast, we have a substantial fossil record of life's development which shows a number of clear pattern, including a steady increase in biodiversity towards the present, punctuated by a number of large extinction events which wiped out a significant fraction of the species on the planet and in some cases caused major reorganizations amongst the dominant groups of organisms in the ecosphere.
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Paper provided by Santa Fe Institute in its series Working Papers with number
99-12-079.