Washington, D.C. Scientists at the Carnegie Institution and Penn State University* have discovered evidence showing that microbes adapted to living with oxygen 2.72 billion years ago, at least 300 million years before the rise of oxygen in the atmosphere. The finding is the first concrete validation of a long-held hypothesis that oxygen was being produced and consumed by that time and that the transition to an oxygenated atmosphere was long term. The results are published in the on-line early edition of the Proceedings of the National Academy of Science, to appear the week of October 16th.
It is generally believed that before 2.4 billion years ago, Earth's atmosphere was essentially devoid of oxygen. Exactly when and how oxygen-producing photosynthesis evolved and began fueling the atmosphere with the gas that much of life depends on has been hotly debated for some time. Plants, algae, and cyanobacteria (blue-green algae) emit oxygen as a waste product of photosynthesis--the process by which sugar, essential for nutrition, is made from light, water, and carbon dioxide.
"Our evidence points to the likelihood that Earth was peppered with small 'oases' of shallow-water, oxygen-producing, photosynthetic microbes around 2.7 billion years ago," stated lead author Jennifer Eigenbrode of Carnegie's Geophysical Laboratory, who collected the data while pursuing her Ph.D. at Penn State. "Over time these oases must have expanded, eventually enriching the atmosphere with oxygen. Our data record this transition."
The researchers discovered changes in fossil isotopes of the life-essential element carbon in a 150 million-year section of rock that included shallow and deepwater sediments from the late Archean period (the Archean lasted from 3.8 to 2.5 billion years ago) in Hamersley Province in Western Australia. Isotopes are different forms of an element's atoms. The relative proportions of carbon and other isotopes in organic matter depend on c
Contact: Jennifer Eigenbrode