Somewhere around 2.4 to 2.8 billion years ago life on earth began to produce oxygen, thus giving many aerobic organisms the ability to live on earth ... or did it? While many of the details remain the same, recent research has shown that life first gave rise to oxygen not between two and three billion years ago, but approximately 3.02 billion years ago, disrupting a theory that was long taken for granted. This research was performed by scientists at Trinity College Dublin and Presidency University in Kolkata, India and was published in the most esteemed geology journal, Geology. The researchers discovered that oxygen arose an astounding 60 million years earlier than previously thought, which is quite a significant amount of time given that humans have only existed for 200,000 years.
How did the scientists make this discovery, given that the prior research was so well-established and that the conditions on our planet today are drastically different from when oxygen first arose? They used the commonly known radioactive isotope dating system to look at the amounts of uranium and lead present in soil samples that were created from rocks that broke down due to the effects of oxygen’s debut into the atmosphere. The technical name for this soil is paleosol, and the paleosol used in this research originated in Singhbhum Craton of Odisha, an area in India. The soil is often called “Keonjhar Paleosol” after a town nearby. Generally the more rocks in the region that were in soil form rather than rock form, the more oxygen present at the time. The rocks had remained in rock form because the mixture of gases in the air consisted of mainly carbon dioxide and methane with little to no oxygen. The oxygen itself arose from the conversion of carbon dioxide and light energy into oxygen and water, a transformation that was crucial three billion years ago and continues to remain vital for every second of life today. The air on earth today is approximately 20 percent oxygen, a major leap from the air composition three billion years ago.
This finding will not only result in a change in biology textbooks, but it also influences a commonly accepted view of early life on earth. Specifically the research reveals that the atmosphere, which went through several complicated and long-lasting stages in order to exist how it does today, spent a different amount of time in some of those stages than was previously expected. The beginning of oxygen production, often called “The Great Oxidation Event” and “The Oxygen Revolution,” is one of the most frequently referenced of those stages. Life on earth existed earlier than three billion years ago, but the microorganisms present at that point lacked the ability to photosynthesize or produce oxygen. After the first photosynthetic cycle first performed by cyanobacteria, oxygen levels fluctuated for years due to factors like climate and volcanic activity and did not stabilize until much more recently.
A discovery about the early atmosphere likely could not be possible without the use of soil samples dating back to that time, which are incredibly rare. The sample used in this study existed at least 3.02 billion years ago, and there are a small number of samples that are older than even 2.5 billion years. The reason these samples are so helpful is that their chemical composition often mirrors what is occurring in the atmosphere surrounding them, and the absence of ancient soil samples would make research about the early stages of life on earth incredibly difficult.
