Earth’s dramatic climate shifts between frozen “icehouse” periods and warm “greenhouse” states over hundreds of millions of years have been shaped not only by volcanic activity but also by the way tectonic plates move across the planet, a new study has found.

The research, published in Communications Earth and Environment, suggests that regions where tectonic plates pull apart — such as mid-ocean ridges and continental rifts — have played a far more significant role in regulating atmospheric carbon dioxide than previously understood.

Scientists have long linked long-term climate change to fluctuations in atmospheric carbon dioxide, with volcanic arcs at converging plate boundaries considered the primary source of carbon emissions.

However, the new study challenges this view by highlighting the importance of the “deep carbon cycle”, in which carbon is stored in ocean sediments and recycled back into Earth’s interior through tectonic processes.

The researchers used computer models to track how carbon stored on tectonic plates has moved between Earth’s interior, oceans and atmosphere over the past 540 million years.

They found that during greenhouse periods, more carbon was released into the atmosphere than was trapped in rocks and sediments, leading to warmer global temperatures.

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In contrast, icehouse periods were marked by dominant carbon sequestration in the oceans, reducing atmospheric carbon dioxide and driving cooling.

A key finding is the central role of deep-sea, carbon-rich sediments. Oceans absorb large amounts of carbon dioxide from the atmosphere, much of which becomes locked into sedimentary rocks on the seafloor. As tectonic plates move, these sediments are eventually carried into subduction zones, where they release carbon back into the atmosphere over geological timescales.

The study also revises the role of volcanic arcs.

While emissions from these arcs have been a major source of atmospheric carbon dioxide over the past 120 million years, the researchers found this dominance is relatively recent. It is largely linked to the evolution and spread of planktic calcifiers—microscopic marine organisms that began sequestering vast amounts of carbon into seafloor sediments around 200 million years ago.

Before their emergence, carbon emissions from mid-ocean ridges and continental rifts were a more significant contributor to atmospheric carbon dioxide.

The findings offer a new framework for understanding Earth’s climate system, showing it is governed by a balance between carbon released at the surface and carbon locked away in ocean sediments. Researchers say this long-term perspective is crucial for improving climate models and understanding how natural carbon cycles interact with human-driven climate change.

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