How Did Life Start On Earth? Phosphorus May Have Triggered Development As It Migrated From Ocean Depths

All it probably took was a little bit of fertilizer to get life started on Earth, scientists at the Georgia Institute of Technology and Yale University found.

A study published this week in Nature indicates the ingredients for animal life were available for more than 2 billion years before multicelled organisms began evolving. Then 800 million years ago, phosphorus began accumulating in shallow ocean areas near coastlines, apparently setting off chemical chain reactions that pumped oxygen into the atmosphere and oceans, jumpstarting the development of organisms that had more than one cell.

Without saying phosphorus necessarily started the chain reactions, the researchers said sedimentary and fossil records indicate the timing is “conspicuous.”

The work is aimed at explaining what allowed life to develop on Earth and lay a foundation for predictions on what would allow life to develop on exoplanets. It also would help explain how oceanic-atmospheric chemistry influences climate and biodiversity.

Chris Reinhard, an assistant professor in Georgia Tech's School of Earth and Atmospheric Sciences, Noah Planavsky, a geochemist from Yale University, and a team of international researchers examined sedimentary rock in ancient coastal zones, looking at each layer and going back 3.5 billion years.

Life began to blossom in the late Proterozoic Eon, when cyanobacteria began consuming phosporus and pumping oxygen into the atmosphere.

"The most basic change was from very limited phosphorous availability to much higher phosphorus availability in surface waters of the ocean," Reinhard told Phys.org. "And the transition seemed to occur right around the time that there were very large changes in ocean-atmosphere oxygen levels and just before the emergence of animals."

"The only reason we have a well-oxygenated planet we can live on is because of oxygenic photosynthesis," Planavsky said. "[Oxygen] is the waste product of photosynthesizing cells, like cyanobacteria, combining [carbon dioxide] and water to build sugars."

Though cyanobacteria were around for 2.5 billion years or more, the basic nutrients to feed it weren’t initially available, scientists speculate. The phosphorus also was around, but it was trapped in the ocean depths.

"Phosphorus is not only essential for life," Planavsky said. "What's implicit in all this is: It can control the amount of life on our planet."