Rock Discovery Unlocks Secrets of Ancient Carbon Cycle

If Earth's history were condensed into a single year, humans would only appear in the final seconds of December 31st. During the Proterozoic Eon, which spanned from 2.5 billion to 543 million years ago, the Sun was much weaker, and a stronger greenhouse effect was needed to keep the planet warm enough for life to exist.

New research led by Emily Stewart, an Assistant Professor at Florida State University, challenges the long-held belief that volcanic activity was the main source of warmth in Earth’s early history. Stewart’s findings suggest that metamorphic rocks played a key role by releasing carbon dioxide into the atmosphere, which contributed significantly to the planet's greenhouse effect.

In a study published in the Proceedings of the National Academy of Sciences, Stewart and Donald Penman of Utah State University showed that the release of CO2 from metamorphic rocks—a process called metamorphic off-gassing—was far more influential than previously understood. Their research revealed that this carbon release would have created an atmosphere with CO2 levels up to four times higher than pre-Industrial levels.

The research team used computer simulations to model how metamorphic rocks, when subjected to heat and pressure, released carbon dioxide, warming the planet. This process helped create the necessary conditions for the first forms of life to survive in the Proterozoic.

Before this study, scientists largely attributed early atmospheric CO2 to volcanic activity. However, Stewart’s work shows that rocks played a more active role in regulating Earth’s carbon than once thought, acting as both a source and a sink for carbon.

Penman added that metamorphic decarbonation, the release of CO2 from rocks, had been viewed as a secondary process in the carbon cycle. This new research, however, highlights its significance in altering atmospheric CO2 levels and influencing the climate.

To test these findings further, Stewart and her team will conduct field research in Ontario, Canada, focusing on the Central Metasedimentary Belt to gather more evidence. Stewart believes studying these ancient geological processes is crucial to understanding both Earth's past climate and how carbon cycling might help address the challenges of climate change today.