Forests stabilised Earth's CO2 levels millions of years ago
Researchers in the UK have identified a biological mechanism that could explain how the Earth's atmospheric carbon dioxide and climate were stabilised over the past 24 million years.
When CO2 levels became too low for plants to grow properly, forests appear to have kept the climate in check by slowing down the removal of carbon dioxide from the atmosphere.
"As CO2 concentrations in the atmosphere fall, the Earth loses its greenhouse effect, which can lead to glacial conditions," lead-author Joe Quirk from the University of Sheffield, said.
"Over the last 24 million years, the geologic conditions were such that atmospheric CO2 could have fallen to very low levels a€" but it did not drop below a minimum concentration of about 180 to 200 parts per million. Why?" he said.
Before fossil fuels, natural processes kept atmospheric carbon dioxide in check.
Volcanic eruptions, for example, release CO2, while weathering on the continents removes it from the atmosphere over millions of years.
Weathering is the breakdown of minerals within rocks and soils, many of which include silicates.
Silicate minerals weather in contact with carbonic acid (rain and atmospheric CO2) in a process that removes carbon dioxide from the atmosphere.
Further, the products of these reactions are transported to the oceans in rivers where they ultimately form carbonate rocks like limestone that lock away carbon on the seafloor for millions of years, preventing it from forming carbon dioxide in the atmosphere.
The findings are published in Biogeosciences, an open access journal of the European Geosciences Union (EGU).
(Posted on 25-01-2014)