12 nov 541093808 av. J.-C. - Cambrian Explosion

Description:

The apparent sudden diversification of life on earth, from simpler organisms to complex multicellular ones with multiple layers of tissue in the embryo, indicated by the appearance of a great number of fossils in the fossil record within a short period of time.

Especially of note is the divergence of bilaterally symmetrical, triploblastic (three embryonic tissue layers) animals, from which chordates would eventually arise. These bilaterians also began to burrow into the sea floor, altering its structure and composition. While bilaterally similar organisms and likely even the further derived protostomes and deuterostomes were already present before this point, it is likely this was an important period of radiation for them.

Freshwater habitats, from which land-going chordates would eventually emerge, were also colonized during this time.