Origin of Photosynthesis

Photosynthesis, the process by which photosynthetic organisms convert light energy into chemical energy, likely began around 3.5 billion years ago.

The earliest form of photosynthesis was likely anoxygenic, using several alternative electron donors, such as hydrogen sulfide or ferrous iron, and releasing sulfur or oxidized iron rather than oxygen.

Later, cyanobacteria evolved the ability to perform oxygenic photosynthesis using water as an electron donor and releasing oxygen as a byproduct.

Oxygen released by cyanobacteria reacted with dissolved iron in the oceans, forming insoluble iron oxides that settled as banded iron formations on the seafloor.

Meanwhile, cyanobacteria formed layered microbial mats, which eventually fossilized into stromatolites.

As most of the ocean’s dissolved iron oxidized and major oxygen sinks in the oceans became increasingly saturated, free oxygen was eventually able to accumulate in the atmosphere.

This rise in atmospheric oxygen triggered the Great Oxidation Event about 2.4 billion years ago, enabling aerobic metabolism and ozone layer formation.