What Earth’s Deep Past Teaches Us About Climate Balance

How carbon moved through Earth’s interior, oceans, and atmosphere over 540 million years

Image from CANVA

For decades, scientists have known that Earth’s long-term climate swings are tied to carbon moving through the planet. When more carbon accumulates in the atmosphere, temperatures tend to rise. When carbon is removed and stored elsewhere, ice expands. This basic relationship has been one of the most reliable anchors in climate science.

To make sense of it across hundreds of millions of years, researchers focused on processes that leave clear traces in the geological record. Volcanic arcs, belts of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above, release carbon dioxide as molten rock rises to the surface.

Mountain building exposes fresh rock that reacts with rain and slowly removes carbon from the air. The balance between these two forces offered a powerful way to explain why Earth sometimes lived in greenhouse conditions and other times slipped into icehouse states.

Carbon-silicate cycle feedbacks — By Gretashum — Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=79674633

Over time, however, a quiet puzzle emerged. Some major cooling events happened when volcanic activity was still widespread. Some long warm periods persisted even as continents were being heavily eroded. The mechanisms were sound, but the timing did not always line up as cleanly as expected.

This was not a crisis for the field. It was a signal that the system might be larger than the parts we were emphasizing.

The shared assumption was easy to understand. Continents dominate the surface we live on, and they preserve their history well. Mountain belts remain standing for tens of millions of years. Volcanic arcs leave thick piles of lava and ash. These features are accessible, mappable, and datable. They naturally became the backbone of long-term climate explanations.

There was also a strong intuitive appeal. Volcanoes are visible sources of gas. Mountains look like efficient machines for grinding down rock. When one process seemed to win over the other, climate responded. The story felt complete because it connected cause and effect in ways that matched both observation and instinct.

What was less visible was what happened far from land.

How carbon moves between Earth’s interior and the surface over the last 540 million years. (a) The top panel shows the main ways carbon enters the atmosphere. Carbon is released at mid-ocean ridges and continental rifts, where tectonic plates pull apart, and at volcanic arcs, where one plate sinks beneath another. Volcanic arc emissions are split into two sources: carbon released from sinking oceanic plates and carbon released when magma passes through carbonate-rich rocks. Together, emissions from mid-ocean ridges and rifts make up the carbon released at spreading plate boundaries. (b) The middle panel shows where carbon is stored inside oceanic plates before being recycled back into the Earth. Carbon can be locked into deep-sea carbonate sediments, altered oceanic crust, and parts of the upper mantle that interact with seawater as plates bend, spread, or chemically change. Only a portion of this carbon originally comes from the atmosphere. © The bottom panel shows how much of this stored carbon is carried back into the mantle at subduction zones. This recycling depends on how much carbon is stored in plates and how fast and how extensively plates sink. After about 120 million years ago, carbon recycling increases sharply as deep-sea carbonate sediments become more abundant. The color bar at the top shows geological time and highlights warmer greenhouse periods and cooler icehouse periods — Mather et al., 2025

The ocean floor covers most of the planet, but it is constantly recycled. New crust forms along long underwater ridges, while old crust sinks back into the mantle at subduction zones. For much of Earth’s history, this seafloor record has been erased. That made it harder to place oceanic processes on the same footing as continental ones.

Still, scientists knew they mattered. Mid-ocean ridges release gases as new crust forms. Continental rifts allow carbon to escape as the land stretches and fractures. At the same time, carbon from the atmosphere dissolves into seawater, becomes part of sediments, and is carried back into the Earth when plates sink. These processes were understood individually, but rarely combined into a single long-term picture.

The deeper question became harder to ignore. Over geological time, what actually controls whether carbon ends up in the atmosphere or locked away inside the planet?

Answering that question required shifting attention from individual sources to the balance between inputs and storage. It also required accepting that the nature of the carbon cycle itself has changed through time.

Maps where carbon was being released to the atmosphere and where it was being recycled back into the Earth during several well-known climate states in Earth’s history. Colors along plate boundaries show carbon moving into the Earth at subduction zones, where oceanic plates sink, and carbon moving out of the Earth at mid-ocean ridges, continental rifts, and volcanic arcs. Green areas mark carbonate platforms, which are regions where carbon-rich sediments accumulate in shallow seas and can later interact with volcanism. Where subduction zones intersect these platforms, volcanic arcs tend to release more carbon because rising magma dissolves carbon from the surrounding rocks. Each panel represents a different moment in time: (a) the present day, during the Cenozoic icehouse; (b) 60 million years ago, a warm Early Paleogene climate; © 80 million years ago, a relatively cooler phase within the Late Cretaceous; (d) 130 million years ago, during an extended greenhouse period; (e) 300 million years ago, at the height of the Late Paleozoic icehouse; (f) 400 million years ago, during an Early Devonian greenhouse; and (g) 500 million years ago, an early Paleozoic greenhouse world. Together, the panels show how the geography of plates, sediments, and volcanism changes the balance between carbon release and storage through time — Mather et al., 2025

One of the most important changes came from life. Early oceans did not contain large amounts of carbonate sediments. Those sediments became widespread only after microscopic plankton evolved shells made of calcium carbonate. Once that happened, carbon began to accumulate on the seafloor in much larger quantities.

This matters because carbonate sediments are not passive. When they are carried toward subduction zones, some of that carbon can be released back into the atmosphere through volcanism. But if those sediments were rare in the distant past, then volcanic emissions from certain sources must also have been smaller than what we see today.

This realization challenged a common shortcut. Modern volcanic emissions had often been scaled backward in time under the assumption that the same processes operated similarly in the past. The growing evidence suggested otherwise.

At the same time, reconstructions of plate motions were improving. Scientists were able to estimate how fast plates spread, how long mid-ocean ridges were at different times, and how frequently continents pulled apart. These factors directly affect how much carbon is released from Earth’s interior.

When researchers began placing these pieces side by side, a new pattern appeared. Across much of Earth’s history, emissions from mid-ocean ridges and continental rifts were not a steady background. They rose and fell in step with major climate transitions.

Plate tectonic statistics through the Phanerozoic. a Lengths of mid-ocean ridges (blue), subduction zones (orange), continental arcs (red), and carbonate platforms which intersect continental arcs (green). b Spreading and convergence rates along MORs and subduction zones, respectively. c Rates of crustal production at MORs (blue) compared to crustal destruction rates at subduction zones (orange). Red — blue gradients indicate greenhouse — icehouse climates — Mather et al., 2025

Equally important was what happened on the other side of the ledger. During well-known icehouse periods, large amounts of carbon were being stored in oceanic plates faster than it was being released. Cooling did not require volcanism to shut down. It required burial to outpace emissions.

This reframes the problem. Earth’s climate history is not driven by a single dominant process. It is governed by the balance between many processes that shift as plates move, oceans evolve, and life changes the chemistry of the planet.

A recent study adds support to this broader picture by attempting something that had rarely been done before. Instead of focusing on one source of carbon, it tracks both emissions and sequestration across the entire plate tectonic system for the last 540 million years.

The key idea is simple. At any given time, is Earth releasing more carbon into the atmosphere than it is locking into oceanic plates, or the reverse? When the balance tips toward release, greenhouse conditions tend to follow. When storage dominates, ice expands.

Icehouse–greenhouse climate states in the Phanerozoic. Changes in the concentration of atmospheric carbon are driven by the cycling of carbon between the Earth’s mantle and surface. a Variations in surface temperature (black line) and the seawater 87Sr/86Sr curve (magenta line). b Atmospheric CO2 concentration from a compilation of sources (black line) overlain with CO2 estimates from phytoplankton (red circles). c The ratio of atmospheric outflux to oceanic plate influx (from this study) superimposed with the magnitude of glaciation events measured by the latitudinal extent of ice sheets from poles to the equator. Where the carbon outflux /influx ratio is above 1 predicts a greenhouse climate; where the ratio is below 1 predicts an icehouse climate — Mather et al., 2025

What makes this approach compelling is not precision, but consistency. The balance between these two flows aligns with most major climate states in Earth’s past, from early Paleozoic warmth to late Paleozoic ice, from Mesozoic greenhouse conditions to the cooling of the Cenozoic.

This does not overturn earlier work. Continental arcs, mountain building, and weathering still matter, especially in the more recent past. What changes is the scale at which we view them. They are part of a larger system that includes oceanic crust, biological innovation, and the slow recycling of the seafloor.

Seen this way, Earth’s climate stability emerges from interaction, not dominance. No single process controls the outcome on its own. Climate responds to how carbon moves through the whole planet, not just the parts we see most easily.

That perspective carries a quiet lesson. Understanding Earth’s past does not require more dramatic explanations. It requires broader ones. When we widen the frame, the apparent inconsistencies begin to make sense, and the planet’s long climate story becomes clearer, not more complicated.

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