Patterns of Extinction and Biodiversity in the Fossil Record

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.