The two Earlist phases of Multi-celled Organism Evolution
Ediacarian fauna 570-543 m yrs (New Scientist 18 Oct 1997). There is continuing debate about the nature of the Ediacarian fossils and their link to the richly diversifying Cambrian. Genetic molecular clocks suggest a more gradual diversification consistent with the major phylla we experience today having a pre-Cambrian origin, however the genetic data is somewhat inconsistent. Comparisons of globin suggest a common origin around 900 million years ago while 18s ribosomal RNA studies suggest a more recent simultaneous origin before the Cambrian. (Scientific American Nov 92) These all pivot on the delicate question of whether mutational rates can be assumed to be relatively constant over time. Since DNA repair is a differential factor among organisms and stresses vary extensively over periods of beneficent or extreme conditions, this is possibly unlikely. Some other researchers allege the Ediacarian fossils lacked the body plan architecture of Cambrian organisms.
The Cambrian Radiation 543-510 m yrs was responsible for a massive diversification into new body plans, many of which are unique to the epoch and others of which are the founders of our major orders. Some religious thinkers try to use the apparent suddenness of the Cambrian radiation to imply a sudden creation but this may simply manifest the development of the homeotic plan of embryogenesis so that it became capable of mutational 'theme and variation'.