Study shows 3.2 billion-year-old Iron-bearing rocks carry unmistakable evidence of oxygen

Study shows 3.2 billion-year-old Iron-bearing rocks carry unmistakable evidence of oxygen

According to a new study, iron-bearing rocks that formed at the ocean floor 3.2 billion years ago carry unmistakable evidence of oxygen. University of Wisconsin-Madison geoscientists said that the only logical source for that oxygen is the earliest known example of photosynthesis by living organisms.

Clark Johnson, a professor of geoscience at UW-Madison and a member of the NASA Astrobiology Institute, said that the rocks from 3.4 billion years ago have shown that the ocean contained basically no free oxygen.

Johnson said, “Recent work has shown small rise in oxygen at 3 billion years. The rocks we studied are 3.23 billion years old and quite well preserved, and we believe they show definite signs for oxygen in oceans much earlier than previous discoveries”.

Cyanobacteria, primitive photosynthetic organisms that lived in the ancient ocean, were the most reasonable candidate for liberating the oxygen discovered in the iron oxide. Presently, the earliest proof for life dates back 3.5 billion years, so oxygenic photosynthesis may have evolved relatively soon after life itself.

The conventional wisdom in geology till recently held that oxygen was not common until the ‘great oxygenation event’ that took place 2.4 to 2.2 billion years back.

During the study, the researchers studied the rocks known as jasper, made of iron oxide and quartz. The rocks showed regular striations caused by composition changes in the sediment that created them. The UW-Madison scientists for the detection of oxygen measured iron isotopes with a sophisticated mass spectrometer, with a hope to find out how much oxygen was required in the formation of the iron oxides.

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