14 DAY TRIAL // Our planet seems to have filled its lungs with oxygen 50 to 100 million years before previously believed. Two new researches show that low levels of oxygen were already present in the oceans and possibly in the atmosphere around 2.5 billion years ago, pointing to the fact that oxygen-releasing microbes, like cyanobacteria, were already producing the gas. It was thought that the boom of these organisms caused the sudden rise of oxygen on Earth, event known as the Great Oxidation, 2.3 to 2.4 billion years ago. The question is why were there required 100 million years for the oxygen boom? Possibly because of various geological processes.
"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 Carl Pilcher, director of the NASA Astrobiology Institute, not involved in these researches.
The evolutionary boom of life on Earth is closely linked to the presence of oxygen in the atmosphere. But environmental changes before the Oxidation Event had remained a puzzle. To explain this, the two teams investigated layers of rock in a 3,000-foot-long (914 meters) core drilled from the Hamersley Basin (Western Australia), where one of the oldest rocks on Earth are found.
They focused on chemicals connected with an oxygenated environment, like sulfur compounds and some metals (such as molybdenum and rhenium). The researchers encountered proofs that there was a low but significant oxygen quantity present in the oceans and perhaps also in the Earth's atmosphere just before the end of the Archean Eon (about 3.9 billion to 2.5 billion years ago), when microbial life emerged and diversified.
"Together, these [studies] provide compelling evidence for a shift in the oxidation state of the surface ocean 50 million years before the Great Oxidation Event. We believe that these findings are a significant step in our understanding of the oxygenation of Earth because they link changes in the environment with that of the biosphere.", said Alan Jay Kaufman, a geochemist at the University of Maryland and lead author of the second new study.
"The data show that oxygen existed in the environment before the Great Oxidation Event and strongly suggests that photosynthesis that produced oxygen was around before then," Ariel Anbar, a biogeochemist at Arizona State University, lead author of one of the studies, told LiveScience.
Non-biological phenomena could also be involved. "Photochemical processes, in which chemical reactions are driven by different wavelengths of light, can lead to changes in the relative amounts of different forms of sulfur, for instance.", said Andrey Bekker of the Carnegie Institution of Washington, not involved in either of the current studies.
Geological processes could have kept the released oxygen in check for millions of years before the Great Oxidation Event. "Why didn't oxygen rise in the atmosphere as soon as that metabolism evolved? There are geological processes that consume oxygen, so even when biology is pumping it into the environment it doesn't necessarily rise strongly in the atmosphere right away", Anbar added.
Some volcanic gases can consume oxygen, and variations in the volcanic activity over time could explain variations of oxygen in the atmosphere.