Life forms appeared at least 60 million years earlier than previously thought
Geologists have rewritten the evolutionary history books by finding that oxygen-producing life forms were present on Earth some 3 billion years ago, a full 60 million years earlier than previously thought. These life forms added oxygen to our atmosphere, which laid the foundations for more complex life to evolve and proliferate
Working with Professors Joydip Mukhopadhyay and Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, the geologists 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.