Coral reefs have helped control earth’s climate for 250 million years

For more than a quarter billion years, coral reefs did far more than brighten shallow seas. Long before humans appeared, these living structures helped guide how Earth recovered from major climate shocks. New research shows reefs played a quiet but powerful role in setting the rhythm of the planet’s carbon cycle.

The study reveals that shallow-water reef systems influenced how quickly Earth stabilized after massive carbon dioxide changes. These ancient ecosystems did not simply react to climate shifts. They helped control how long recovery took.

Scientists from the University of Sydney and Université Grenoble Alpes traced these patterns back to the Triassic Period, more than 250 million years ago. Their work connects reef growth, ocean chemistry, and climate recovery in a way not fully understood before.

“Reefs didn’t just respond to climate change, they helped set the tempo of recovery,” said Associate Professor Tristan Salles of the University of Sydney’s School of Geosciences.

Carbon dioxide has long shaped Earth’s temperature. When large amounts enter the atmosphere, the planet warms. When carbon is removed, cooling follows. Scientists have traditionally focused on land-based rock weathering as the main long-term control of this process. This new research points to the ocean, especially shallow tropical seas, as another major player.

"Reefs and other carbonate systems build structures from calcium carbonate. That same material locks carbon away. Where this carbonate forms and settles matters deeply for how the planet regulates itself. Our research team combined plate movement maps, climate models, surface process data, and ecological simulations. Together, these tools allowed us to recreate how shallow seas produced carbonate over vast stretches of time, Salles told The Brighter Side of News.

"What we found was a repeating pattern. Earth’s climate system shifted between two distinct modes that shaped how fast recovery occurred after carbon disruptions," he added.

In the first mode, warm shallow seas spread widely across tropical regions. Reefs flourished. Carbonate built up mostly in coastal waters. At first glance, this seems helpful. Yet this abundance created an unexpected effect. When carbonate piled up near shore, it limited chemical exchange with the deep ocean. This weakened the biological pump, a process where marine life helps move carbon from surface waters into the depths.

With that system slowed, excess carbon lingered longer in the atmosphere. Climate recovery stretched on. In these periods, Earth healed slowly after carbon shocks. Recovery could take tens of thousands of years, sometimes longer. The second mode unfolded very differently. When tectonic shifts or sea level changes reduced shallow reef space, carbonate production near shore dropped. Calcium and alkalinity built up in ocean water instead.

That excess then moved into the deep sea. There, tiny organisms called nannoplankton used the material to build their shells. When they died, their remains sank, pulling carbon downward more efficiently. This strengthened the biological pump and sped up climate recovery. “These switches profoundly alter the biogeochemical equilibrium,” said co-lead author Dr. Laurent Husson of CNRS at Université Grenoble Alpes.

These shifts did not happen randomly. They followed changes in ocean shape, sea level, and plate movement. The study shows that when shallow reefs declined, plankton life often expanded. When reefs grew again, plankton productivity slowed. “The big expansion of planktonic life happened exactly when shallow reefs were turned down by the Earth system,” Husson said.

This connection reshapes how scientists view marine evolution. Reefs were not just victims of climate change. They were active participants in shaping ocean chemistry, marine life, and long-term temperature stability. Over millions of years, this balance influenced which organisms thrived and which faded. The ocean’s chemistry, biology, and climate moved together like parts of the same engine.

The researchers tracked these cycles across enormous spans of time. Their reconstruction stretches from the Triassic Period through the Jurassic, Cretaceous, and into the modern era. During some intervals, especially parts of the Early Cretaceous and the later Cenozoic, shallow reefs dominated carbonate storage.

At other times, including much of the Jurassic and Late Cretaceous, deep-sea burial played the larger role. Each shift changed how fast Earth could respond after large carbon releases, whether from volcanic activity or other natural causes.

These transitions explain why some ancient warming events lingered while others faded more quickly. The planet’s ability to heal depended not only on how much carbon entered the air, but on where life stored it afterward.

Although the study focuses on deep history, its message feels strikingly modern. Today’s coral reefs are disappearing at alarming rates. Rising ocean temperatures and acidification continue to weaken reef systems around the world. If modern reefs collapse in ways similar to ancient events, carbonate burial may again shift away from shallow seas. In theory, this could increase deep-ocean carbon storage. But the study warns against false comfort.

The organisms that once powered deep-sea recovery, including plankton that form carbonate shells, are also threatened by acidifying waters. The system that once helped Earth recover may not function the same way under current conditions. Salles emphasized that geological recovery does not mean human recovery.

“From our perspective on the past 250 million years, we know the Earth system will eventually recover from the massive carbon disruption we are now entering,” he said. “But this recovery will not occur on human timescales.” He added that geological stabilization requires thousands to hundreds of thousands of years.

This research reframes reefs as more than fragile ecosystems at risk today. For much of Earth’s history, they acted as climate regulators. Their growth and decline helped determine how long warming lasted and how oceans recovered. That history adds weight to what is now being lost. Reefs support fisheries, protect coastlines, and hold unmatched biodiversity.

This study shows they also once helped steady the planet itself. Their decline carries consequences that reach far beyond beaches and coral gardens. It touches the deep systems that have guided Earth’s climate for hundreds of millions of years.

The findings help scientists better understand how life influences long-term climate stability. This knowledge improves climate modeling by showing how marine ecosystems affect carbon storage over deep time. It also highlights the importance of protecting reef systems, which play roles beyond biodiversity alone.

The study may guide future research on ocean chemistry, climate resilience, and how biological systems interact with planetary recovery after major environmental disruptions.

Research findings are available online in the journal PNAS.

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