Behind the Iron Curtain: How Methane-Making Microbes Kept the Early Earth Warm

Science and Technology

Earth and Environment

Behind the Iron Curtain: How Methane-Making Microbes Kept the Early Earth Warm






By
John Toon | April 17, 2017
• Atlanta, GA








Click image to enlarge

Marcus Bray (left), a biology Ph.D. candidate and Jennifer Glass, assistant professor in the Georgia Institute of Technology’s School of Earth and Atmospheric Sciences, are shown in the laboratory where tiny incubators simulated early Earth conditions. (Credit: Rob Felt, Georgia Tech)





For much of its first two billion years, Earth was a very different place: oxygen was scarce, microbial life ruled, and the sun was significantly dimmer than it is today. Yet the rock record shows that vast seas covered much of the early Earth under the faint young sun. 

Scientists have long debated what kept those seas from freezing. A popular theory is that potent gases such as methane – with many times more warming power than carbon dioxide – created a thicker greenhouse atmosphere than required to keep water liquid today.

In the absence of oxygen, iron built up in ancient oceans. Under the right chemical and biological processes, this iron rusted out of seawater and cycled many times through a complex loop, or “ferrous wheel.” Some microbes could “breathe” this rust in order to outcompete others, such as those that made methane. When rust was plentiful, an “iron curtain” may have suppressed methane emissions.

“The ancestors of modern methane-making and rust-breathing microbes may have long battled for dominance in habitats largely governed by iron chemistry,” said Marcus Bray, a biology Ph.D. candidate in the laboratory of Jennifer Glass, assistant professor in the Georgia Institute of Technology’s School of Earth and Atmospheric Sciences and principal investigator of the study funded by NASA’s Exobiology and Evolutionary Biology Program. The research was reported in the journal Geobiology on April 17, 2017.

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