In the marine sphere:

Evolution continued a pace in the marine sphere. Algal accumulations called stromatolites became quite common and indicated assemblages of many kinds of prokaryotes living together. These formed the initial kinds of communities along the margins of land as living stromatolites do in Western Australia. But again, these are not terrestrial plant communities although they underwrote an enormous radiation in marine metazoan life about 550 million years ago. We will come back to this radiation of metazoa at the Vendian/Cambrian boundary (Also called the Precambrian/Cambrian boundary) because it gives us the source of both invertebrates and vertebrates that will be players later in the story.

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