This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Life arose on Earth at least 3.5 billion years ago, and our planet has remained habitable ever since—not too hot, not too cold. These life-sustaining conditions are possible in part thanks to a built-in, carbon cycle–based climate "thermostat" that controls the amount of carbon dioxide in the atmosphere.
"There appears to be some kind of balance in what sustains the main greenhouse gas in Earth's atmosphere, keeping the climate at a pretty nice temperature, habitable for life over really long timescales," said R.J. Graham, a postdoctoral scholar in the University of Chicago's Department of the Geophysical Sciences. The process that manages this balance, however, may not be an unchanging mechanism.
In a new study published in Nature Communications, Graham and colleagues from UChicago and the University of Southampton present evidence that this so-called climate thermostat may have operated in one mode for most of the past 480 million years, briefly—by geological standards—flipped modes during the age of Pangea, and then flipped back. If the thermostat mechanism did in fact flip, the scientists said, that change could provide a new perspective on our planet's history and climate mechanisms, as well as the future of life on our planet as the sun brightens. Carbon dioxide is the main long-term controller of Earth's greenhouse effect.
Removing it from the atmosphere essentially turns on the air conditioning, and putting it back turns on the heat. The feedback cycle relies on a process known as silicate weathering. CO₂ in the atmosphere combines with rainwater, turning it slightly acidic, which chemically breaks down rock.
The dissolved minerals and carbon from the CO₂ wash into rivers and oceans, where they form carbonate rocks on the seafloor. Over millions of years, those rocks get carried into Earth's interior through subduction, and carbon gets released by volcanoes as carbon dioxide back into the atmosphere, completing the cycle. Silicate weathering speeds up to cool the planet and slows down to warm it.
But scientists have long debated what exactly is driving the rate—temperature or rainfall? Does warmer rock simply react more quickly, or is weathering more affected by the amount of water washing over rock and through soil? In the version of events where temperature is the main driver, weathering is primarily affected by heat.
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