Photosynthesis May Have Started Later

Oct. 23, 2008 -- Oxygen-producing photosynthesis may not have been around as long as previous studies suggest, according to Australian researchers. But not all are convinced.

"Without oxygen we wouldn't have the development of more complex aerobic life -- multicellular life. So [its production is] a really important event in Earth's history," said Birth Rasmussen of Curtin University of Technology in Perth.

Rasmussen and colleagues report their findings in this week's issue of the journal Nature.

Nearly a decade ago, co-author Jochen Brocks, of the Australian National University in Canberra, and colleagues reported evidence of photosynthesis in 2.7 billion-year-old rocks from Western Australia's Pilbara region in the journal Science.

They reported finding "biomarkers," molecular fossils, including hydrocarbons such as hopane and sterane, believed to come from the membranes of photosynthetic cyanobacteria.

This landmark study pushed evidence for oxygen-producing cyanobacteria back by 300 million years and presented scientists with a conundrum.

Related Content:

It was not until 2.45 to 2.32 billion years that the first major rise in atmospheric oxygen occurred, as recorded in the Great Oxidation Event -- a mass oxidation of minerals in the Earth.

"If you had oxygen-producing cyanobacteria at 2.7 [billion years ago] churning out oxygen, why did it take so long -- why did it take 300 million years -- before we see the results of that?"

The biomarker study also set back the age of the rise of eucaryotes by a billion years, long before the Great Oxidation Event.

All in all it created "a yawning palaeontological divide," said Woodward Fischer of the California Institute of Technology, in a commentary accompanying the new study by Rasmussen and his team.