Life may have begun on land not in the sea, Multicellular fossils, ancestors of marine life, lived on land. These were microbial colonies like lichen. Ediacaron fossils over 600 million years old have been found in South Australia.
High-tech investigative technology showed the ancient forebears lived on land. The soil they were in had "old elephant skin' over it. This phenomenon forms in sandstone beds. It is much like the surface of modern sandy deserts with close wavy lines.
Ediacaran fossils were direct ancestors of marine animals, not mammals. The chain of life leading to humans came during the Cambrian era long after these old multicellular fossils. Apparently, the presence of salt and even too much water are barriers to initial life formation. There was more animals diversity on land than in the sea during the Cambrian.