Researchers at the University of Washington have determined that “some” microbial life migrated from the Earth’s oceans to land some 2.75 billion years ago. 

However, a number of scientists continue to hypothesize that such land-based life was limited – at least initially – because the ozone layer that shields against ultraviolet radiation didn’t form until hundreds of millions years later.

 Nevertheless, researchers now believe early microbes might have been widespread on land, effectively producing oxygen and weathering pyrite, an iron sulfide mineral, which released sulfur and molybdenum into the oceans.