Earth’s climate has oscillated for hundreds of millions of years between cold “icehouse” states and warm “greenhouse” periods, largely in response to changes in atmospheric carbon dioxide. Volcanoes are often assumed to have played a constant role in regulating this balance, but new modelling research suggests their climatic influence—particularly from volcanic arcs—emerged much later in Earth’s history than previously believed. This work reframes how scientists understand the deep carbon cycle and its evolving connection to life, tectonics, and climate.
Volcanic arcs, such as those found in Japan, release carbon dioxide as tectonic plates sink into Earth’s mantle and partially melt. However, research led by Ben Mather at the University of Melbourne shows that these arcs only became a major carbon source around 100 million years ago, near the end of the dinosaur era. Prior to this, volcanic arcs emitted relatively little CO₂, meaning they were not dominant drivers of long-term climate change.
The turning point occurred around 150 million years ago with the rise of phytoplankton that produce calcium carbonate shells. When these organisms die, their shells accumulate as vast carbonate sediments on the ocean floor. As oceanic crust is later subducted beneath continents, these carbon-rich sediments are carried into Earth’s interior. Some of this carbon is retained in the mantle, while a fraction is returned to the surface through volcanic arc eruptions. This biological innovation fundamentally altered the deep carbon cycle, linking marine ecosystems to long-term volcanic emissions.
By modelling plate tectonics and carbon movement over the past 500 million years, the researchers found that for most of Earth’s history, carbon release was dominated not by volcanic arcs but by rifting. Rifting occurs when tectonic plates pull apart, exposing molten material from the mantle. This process happens both on continents, such as in the East African Rift, and along mid-ocean ridges where new crust forms. Carbon emissions from rifting depend on how fast plates separate and how extensive the rift systems are, but these emissions remained relatively steady over geological time.
In contrast, carbon emissions from volcanic arcs increased dramatically in the past 100 million years. Thanks to the buildup of carbonate sediments produced by plankton, volcanic arcs today emit roughly two-thirds more carbon than they did 150 million years ago. This marks a significant shift in the balance of the deep carbon cycle, with biology indirectly amplifying geological carbon release.
Despite this increase, Earth is currently in a long-term ice age that began around 34 million years ago, interrupted only by short interglacial warm periods. One reason is that phytoplankton continue to remove enormous amounts of carbon from the oceans and lock it into seafloor sediments, outweighing volcanic emissions. Much of this carbon is eventually recycled into the mantle, reinforcing the slow, stabilizing feedbacks of the deep carbon cycle.
Geologist Alan Collins of the University of Adelaide emphasizes that studies like this are crucial for understanding how evolving life forms reshape Earth’s interior–surface connections. As ocean life changed the composition of sediments, it also reshaped how volcanism, tectonics, and climate interact over deep time—revealing a planet whose climate history is inseparable from the evolution of life itself.