Washington: Scientists have re-written the history of evolution with their new discovery which claims that oxygen-producing life forms actually appeared on Earth 3 billion years ago, which is 60 million years earlier than previously thought.
Geologists from Trinity College Dublin along with Professors Joydip Mukhopadhyay, Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, found evidence for chemical weathering of rocks leading to soil formation that occurred in the presence of O2. Using the naturally occurring uranium-lead isotope decay system, which is used for age determinations on geological time-scales, the authors deduced that these events took place at least 3.02 billion years ago. The ancient soil (or paleosol) came from the Singhbhum Craton of Odisha, and was named the 'Keonjhar Paleosol' after the nearest local town.
The pattern of chemical weathering preserved in the paleosol is compatible with elevated atmospheric O2 levels at that time. Such substantial levels of oxygen could only have been produced by organisms converting light energy and carbon dioxide to O2 and water. This process, known as photosynthesis, is used by millions of different plant and bacteria species today. It was the proliferation of such oxygen-producing species throughout Earth's evolutionary trajectory that changed the composition of our atmosphere, adding much more O2, which was as important for the development of ancient multi-cellular life as it is for us today.
Senior author of the research, Quentin Crowley, said that the finding helped to fill a gap in people's knowledge about the evolution of the early Earth. The paleosol from India tells that there was a short-lived pulse of atmospheric oxygenation and this occurred considerably earlier than previously envisaged.
The early Earth was very different to what we see today. Our planet's early atmosphere was rich in methane and carbon dioxide and had only very low levels of O2. The widely accepted model for evolution of the atmosphere states that O2 levels did not appreciably rise until about 2.4 billion years ago. This 'Great Oxidation Event' event enriched the atmosphere and oceans with O2, and heralded one of the biggest shifts in evolutionary history.
Micro-organisms were certainly present before 3.0 billion years ago but they were not likely capable of producing O2 by photosynthesis. Up until very recently however, it has been unclear if any oxygenation events occurred prior to the Great Oxidation Event and the argument for an evolutionary capability of photosynthesis has largely been based on the first signs of an oxygen build-up in the atmosphere and oceans.
The study is published online in the world's top-ranked Geology journal, Geology.
