Washington, Sept 28 : A new NASA funded research has pushed back the timeline for presence of oxygen in the Earth’s atmosphere by 50-100 million years before the Great Oxidation Event.

The event happened between 2.3 and 2.4 billion years ago, when many scientists think atmospheric oxygen increased significantly from the existing very low levels.

As part of their study, the scientists analysed a kilometre-long drill core from Western Australia, representing the time just before the major rise of atmospheric oxygen.

The astrobiologists found evidence of presence of a small but significant amount of oxygen in Earth's oceans and atmosphere 2.5 billion years ago.

“We seem to have captured a piece of time during which the amount of oxygen was actually changing – caught in the act, as it were,” said Ariel Anbar, associate professor at Arizona State University, Tempe, and leader of one of the research teams.

Prof. Anbar said the goal of the research team was to learn more about the environment and life in the oceans leading up to the Great Oxidation Event.

However, the scientists never once did expect to find evidence of oxygen earlier than what was previously known, he said.

“The core provides a continuous record of environmental conditions, analogous to a tape recording,” said Prof. Anbar.

He said the research team analyzed the amounts of the trace metals molybdenum, rhenium and uranium from the core. The quantity of these metals in oceans and sediments depend on the amount of oxygen in the environment.

Another research group led by Alan Kaufman of the University of Maryland, College Park, Md., analyzed sulphur isotopes. Its distribution also relies on the abundance of oxygen.

“Studying the dynamics that gave rise to the presence of oxygen in Earth's atmosphere deepens our appreciation of the complex interaction between biology and geochemistry,” said co-author Carl Pilcher, director of the NASA Astrobiology Institute at NASA's Ames Research Center, Moffett Field, California.

“Their results support the idea that our planet and the life on it evolved together,” said Pilcher.

The scientists said one possible explanation for the Great Oxidation Event could be that ancient ancestors of today's plants first began to produce oxygen by photosynthesis.

However, many geoscientists think organisms began to produce oxygen much earlier, but the oxygen was destroyed in reactions with volcanic gases and rocks.

“What we have now is new evidence for some oxygen in the environment 50 to 100 million years before the big rise of oxygen. Our findings strengthen the notion that organisms learned to produce oxygen long before the Great Oxidation Event, and that the rise of oxygen in the atmosphere ultimately was controlled by geological processes,” said Prof. Anbar.

The findings appear in a pair of research papers in the Sept. 28 issue of the journal Science. (With inputs from ANI)