During Earth’s so-called Archean era, some 2.5- to 3.8 billion years ago, the atmosphere had little oxygen and much more methane, thanks in large part to organisms called cyanobacteria that filled the seas.
Computer models show that methane released by the bacteria left Earth periodically wrapped in an orange blanket of hydrocarbons, the result of sunlight breaking down the methane and molecules recombining in the atmosphere.
A similar phenomenon can be seen today at Saturn’s moon Titan, though its hydrocarbon haze is not tied to biological activity.
“In the later Archean, when there was a lot of methane there were times when our entire planet was enshrouded by hydrocarbons,” Giada Arney, an astronomy graduate student at the University of Washington, said at the American Astronomical Society’s planetary sciences meeting in Maryland this week.
“When we look at Earth through time, we would see that Earth has looked very different at different epochs in its geological history. When we ask the question ‘What does an Earth-like planet look like?’ the answer depends on the time period that we’re thinking about.
“Pale orange dots can be Earth-like planets too,” Arney said.
Baby Earth’s blanket of hydrocarbons helped shield the planet from damaging ultraviolet radiation, much like ozone does today. The haze also helped Earth cool off, by reflecting solar heat back into space. Gradually, Earth’s climate and environment changed, leading to the rich diversity of life that exists today.
Astronomers may be able to find chemical footprints of similar early processes unfolding beyond the solar system.
Read more at Discovery News
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