December 31, 2012 in Offbeat
“Most major animal groups appear for the first time in the fossil record some 545 million years ago on the geological time scale in a relatively short period of time known as the Cambrian explosion. Of great worry to Darwin, the explanation of this sudden, apparent explosion persists as a source of numerous major debates in paleobiology.”
Beginning around 542 million years ago, a profusion of animals with shells and skeletons began to appear in the fossil record. So many life forms appeared during this time that it is often referred to as the “Cambrian Explosion.”
The Cambrian explosion did not occur prior to Mars transition to Earth around half a billion years ago because the planet had not yet reached the habitable zone.
“Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived.”
Life began in the subsurface oceans of Europa and continues to evolve in the oceans beneath Mars.