Ancient rock formations can emit massive amounts of carbon dioxide

For example, rocks can suck up carbon dioxide when certain minerals are attached by the weak acid found in rainwater in a process called chemical weathering. This kind of process can help counter the continuous release of the greenhouse gas released by volcanoes around the world. This is part of the natural carbon cycle that has helped keep the planet habitable for a billion years or longer.

But the study measured another natural process that releases carbon dioxide from rocks to the atmosphere and they found that thus is as big a source of the gas as volcanoes. This process is not yet included in most models of the natural carbon cycle, according to the University of Oxford.

This process happens when rocks that formed on ancient seafloors are pushed back up to the planet’s surface, like what happens when mountains like the Himalayas are formed. The seafloor is where a lot of dead plants and animals are buried in sediments. When that rock rises, it exposes organic carbon to oxygen in the air and water, which can react and release carbon dioxide.

Until now, measuring this release of carbon dioxide from weathering organic carbon in rocks has been quite difficult. For the new study, the researchers used a “tracer element” which is released when organic carbon in rocks reacts with oxygen—rhenium. Of course, it is not possible to sample all the river water in the world to get a global estimate. The researchers used an interesting approach.

They first worked out how much such organic carbon is present in rocks near the surface. They then worked out which of those were being exposed due to erosion in steep mountain locations. They then fed these maps they made along with river data to a supercomputer at Oxford, creating a simulation of the complex interplay of physical, chemical, and hydrological processes. That is how they estimated the carbon dioxide released by these ancient rocks.