title: The reason for as well as the consequence of the Cambrian explosion in animal evolution.
abstract: The first 1 billion years of our 4.5-billion-year-old planet were extremely violent, characterized by constant meteorite bombardment. Therefore, it is with a great surprise that we note that cellular life flourished 3.5 billion years ago. It appears that the cellular life came into being as soon as the earth's environment became hospitable. Because the main ingredient of the Archean sea was sodium bicarbonate, neither archeobacteria nor eubacteria but rather photosynthesizing organisms dominated-initially, prokaryotic cyanobacteria, soon joined by eukaryotic blue-green algae. These consumers of carbon dioxide were also releasers of molecular oxygen. The toil of 3 billion years by these releasers of molecular oxygen finally triggered the Cambrian animal explosion. With exceptions of two animal phyla, Porifera and Coelenterata, which amde slightly earlier appearances, nearly all other extant animal phyla sprang into almost simultaneous existence within 6 to 10 million years. The notion of the Cambrian pananimalia genome was advanced to explain various evolutionary consequences of this Cambrian explosion.
authors.affiliation: Beckman Research Institute, City of Hope, Duarte, CA 91010, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ohno
mesh_terms: D000828:Animal Population Groups; D000818:Animals; D005075:Biological Evolution