ABSTRACT
Both the record of fossils and our ability to date them are now impressive, and improving as new examples and new dating techniques are discovered. Although the preservation of soft tissue from early, small life forms is inevitably limited to a few examples, there is some information about the organisms that lived during the rst 3 billion years of life, before the Cambrian explosion when the diversity of animal life evolved from a few types of primitive organism. After that, there is an abundance of fossils, although never as many species as one might like and often too few of any single species to be able to get a sense of its development, size distribution, and sexual dimorphism, or even its dates of appearance and extinction. Nevertheless, our knowledge of fossils and their dates is good enough to describe much of the history of life.
