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66 Million Year Ocean Calcium Climate Shift

Scientists Solve 66-Million-Year Climate Mystery Behind Earth's Shift From Greenhouse to Ice Age

Scientists uncover a 66-million-year-old secret behind the end of Earth’s greenhouse era. Credit: University of Southampton

Scientists have solved a 66-million-year-old puzzle explaining how Earth shifted from a sweltering, tropical greenhouse into the frozen planet we know today. New research suggests that a sharp decline in oceanic calcium levels following the extinction of the dinosaurs played a decisive role in cooling the planet.

Sharp Drop in Ocean Calcium After Dinosaur Extinction

The international study, led by researchers at the University of Southampton, found that calcium concentrations in seawater fell by more than 50% over the past 66 million years.

Published in the Proceeding of the National Academy of Sciences, the findings indicate that this chemical change may have removed vast amounts of carbon dioxide from the atmosphere, weakening the greenhouse effect and triggering long-term global cooling.

Scientists studied fossilised remains of microscopic marine life recovered from the seafloor. Credit: University of Southampton

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Seawater Chemistry as a Driver of Climate Change

Lead researcher Dr David Evans said the results show that major shifts in seawater chemistry were likely a powerful force shaping Earth's climate history.

How Calcium Levels Shaped Climate

Oceans at the Dawn of the Cenozoic Era

He explained that dissolved calcium levels in the oceans were roughly twice as high at the dawn of the Cenozoic Era, soon after dinosaurs still dominated the Earth, than they are today.

At that time, the oceans behaved very differently, storing less carbon in seawater and instead releasing large amounts of carbon dioxide into the atmosphere.

Falling Calcium and Global Cooling

As calcium concentrations gradually fell, carbon dioxide was drawn out of the air, leading to a sharp decline in global temperatures—by as much as 15 to 20°C.

Global Collaboration and Fossil Evidence

The Southampton-led research team carried out the study alongside scientists from:

  • China
  • The United States
  • Israel (Occupied Palestine)
  • Denmark
  • Germany
  • Belgium
  • The Netherlands

Fossils Reveal Ancient Ocean Chemistry

By analyzing fossilized remains of microscopic marine organisms recovered from deep-sea sediments, the researchers assembled the most comprehensive record of ocean chemistry ever produced.

These fossils, known as foraminifera, revealed a strong connection between calcium levels in seawater and the concentration of carbon dioxide in the atmosphere.

Marine Life and Carbon Storage

Role of Corals and Plankton

Using advanced computer modelling, the researchers demonstrated that elevated calcium levels significantly altered how much carbon was absorbed by marine organisms such as corals and plankton, according to Dr Evans.

This process effectively removed carbon from circulation, locking it away in seafloor sediments and preventing it from returning to the ocean or atmosphere.

Long-Term Carbon Removal From the Atmosphere

As dissolved calcium levels gradually declined over millions of years, the way these organisms formed and buried calcium carbonate on the seabed also changed, said co-author Dr Xiaoli Zhou to Tongji University in China.

She explained that the process actively removes carbon dioxide from the atmosphere and stores it away long term.

This change, she said, may have altered the balance of gases in the air, effectively turning down the Earth's natural thermostat.

Seafloor Spreading and Climate Shifts

The researchers also found that the decline in calcium levels closely tracked a slowdown in seafloor spreading —the volcanic process that continually forms new ocean crust.

As the pace of seafloor creation decreased, the chemical interaction between ocean water and underlying rocks shifted, gradually reducing dissolved calcium levels, said co-author Professor Yair Rosenthal of Rutgers University in the United States.

Rethinking the Drivers of Climate Change

He added that seawater chemistry is usually seen as a response to climate change drivers, rather than a force capable of driving climate change itself.

However, the new findings suggest that shifts in seawater chemistry must be considered to fully understand Earth's climate history.

The researchers say it is possible that deep Earth processes have been responsible for many of the major climate changes seen over geological time.

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