Oceans were filled with oxygen 700 million years earlier than believed

March 17th, 2009 - 2:05 pm ICT by ANI  

Sydney, March 17 (ANI): An international team of geologists has claimed that photosynthesizing life forms created an excess of oxygen in the oceans 700 million years earlier than previous estimates suggest.

According to a report in ABC News, bands of haematite in the Marble Bar Cherst reveal the presence of aerobic bacteria nearly 3.5 billion years ago.

The research pushes back the earliest appearance of photosynthesizing organisms from 2.7 to 3.46 billion years ago.

Microscopic organisms such as cyanobacteria create oxygen as a by-product of photosynthesis.

The timing of their first appearance is hotly debated as it provides clues as to how early life on earth evolved.

Until now, the earliest evidence of photosynthesis was microscopic fossils found in shale rocks in Western Australia dating from 2.7 billion years ago.

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 from tiny crystals of the iron-oxide mineral haematite in a 160-metre-long core section that forms part of the Marble Bar Chert.

Haematite can form in the presence of aerobic (oxygen-loving) bacteria in the water, or by photo-electric processes in the upper 10 metres of seawater.

According to the researchers, haematite crystals in the Marble Bar Chert formed in water at least 200 meters deep, because microscopic analysis of the rocks show no sign of wave action or other structures characteristic of shallow-water sediments.

The orientation and nature of the grains of haematite also show that it precipitated directly from the seawater, rather than forming later from other processes, such as the movement of groundwater, they added.

These data strongly suggest that oxygenic photoautotrophs flourished in the photic zone of the 3.46 billion-year-old oceans and supplied molecular oxygen to the deep water, said the researchers.

Professor Hiroshi Ohmoto from the NASA Astrobiology Institute and Department of Geosciences at the Pennsylvania State University said that other data backs their claim for an early development of photosynthesizing life.

Recently accumulated massive amounts of geochemical and biochemical data can be better explained by a theory postulating the emergence of oxygenic photosynthesis and the development of a fully oxygenated atmosphere in the very early evolutionary stage, said Ohmoto.

Once cyanobacteria appeared in one area of the ocean, it probably took less than 10 million years to fully oxygenate the atmosphere and oceans, he added. (ANI)

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