For many hundreds of millions of years, Earth’s climate has warmed and cooled with natural fluctuations in the level of carbon dioxide in the atmosphere. Over the past century, humans have increased CO2 levels to their highest in 2 million years, mostly by burning fossil fuels and causing ongoing global warming.
New research published in Nature, shows how tectonic plates, volcanoes, eroding mountains and seabed sediment have controlled Earth’s climate in the geological past.
Tectonic processes release carbon into the atmosphere at mid-oceanic ridges – where two plates are moving away from each other – which allows magma to rise to the surface and create new ocean crust.
At the same time, at ocean trenches – where two plates converge – plates are pulled down and recycled back into the depths of the Earth. On their way down they bring carbon back into the Earth’s interior, but also release some CO2 via volcanic activity.
Their model shows that the Cretaceous hothouse climate was caused by very fast moving tectonic plates, which dramatically increased CO2 emissions from mid-ocean ridges.
In the transition to the Cenozoic icehouse climate tectonic plate movement slowed down and volcanic CO2 emissions began to decrease.
They also discovered a more complex mechanism hidden in the conveyor belt system involving mountain building, continental erosion and burial of the remains of microscopic organisms on the seafloor.
As soon as mountains are created, they start being eroded. Rainwater containing CO2 reacts with many types of mountain rocks. Rivers then carry the dissolved minerals into the sea. Marine organisms use the dissolved products to build their shells, which ultimately become a part of carbon-rich marine sediments.
As new mountain ranges formed, more rocks were eroded, speeding up the process. Massive amounts of CO2 were stored away, and the planet cooled, even though some of these sediments were subducted with their carbon degassing through arc volcanoes.