Research, published this week in the journal Nature Geosciences, pushes back the earliest appearance of photosynthesising organisms from 2.7 to 3.46 billion years ago.

The timing of the origin of photosynthesis on the early Earth is greatly debated. It is generally agreed, on the basis of the presence of biological molecules found in shales from the Hamersley Basin, Australia, that oxygenic photosynthesis had evolved 2.7 billion years ago. However, whether photosynthesis occurred before this time remains controversial.

The new evidence

Now a team of Japanese, US and Australian scientists, led by Dr Masamichi Hoashi of the Kagoshima University, Japan, have found evidence for oxygen in ancient sea water from marine sedimentary rocks in the Pilbara region of Western Australia.

The evidence comes in form of haematite crystals and associated minerals within the marine sedimentary rocks preserved in a jasper formation which is interpreted as evidence for the formation of these rocks in an oxygenated water body 3.46 billion of years ago.

The researchers suggest that these haematite crystals formed at temperatures greater than 60 °C from locally discharged hydrothermal fluids rich in ferrous iron. The crystals precipitated when the fluids rapidly mixed with overlying oxygenated sea water, at depths greater than 200 m.

As their findings imply the existence of noticeable quantities of molecular oxygen, they propose that organisms capable of oxygenic photosynthesis evolved more than 700 million years earlier than previously recognized, resulting in the oxygenation of at least some intermediate and deep ocean regions.