Microbial Life Migrated From Earth's Oceans to Land 2.75 Billion Years Ago

New evidence on the microbial life points to migration of microbial life from Earth's oceans to land 2.75 billion years ago. According to the researchers from the University of Washington early microbes might have been widespread on land, producing oxygen and weathering pyrite, an iron sulfide mineral, which released sulfur and molybdenum into the oceans.

But many scientists believe that such land-based life was limited because the ozone layer that shields against ultraviolet radiation did not form until hundreds of millions years later.

"This shows that life didn't just exist in a few little places on land. It was important on a global scale because it was enhancing the flow of sulfate from land into the ocean," said Eva Stueken, a UW doctoral student in Earth and space sciences.

"In turn, the influx of sulfur probably enhanced the spread of life in the oceans," said Stueken.

The details of this study were processed in the Nature Geoscience on Sept 23.

Stueken says that, "Sulfur could have been released into sea water by other processes, including volcanic activity.  But evidence that molybdenum was being released at the same time suggests that both substances were being liberated as bacteria slowly disintegrated continental rocks."

It is likely that land based microbes were producing oxygen before the "Great Oxidation Event" that occurred 2.4 billion years ago. The added sulfur might have allowed marine microbes to consume methane, which triggered atmospheric oxygenation. But prior to that oxygen were destroyed by reacting with methane that rose from the ocean into the air.

"It supports the theory that oxygen was being produced for several hundred million years before the Great Oxidation Event. It just took time for it to reach higher concentrations in the atmosphere," Stueken said.

For the study the researchers worked on data that calculated the sulfur levels in 1,194 samples from marine sediment formations that were recorded before the Cambrian period began about 542 million years ago. 

"The processes by which sulfur can be added or removed are understood well enough to detect biological contributions," the researchers said.

The National Science Foundation and the Virtual Planet Laboratory in the UW Department of Astronomy funded this research