Scientists have solved the 66-million-year-old mystery behind how our planet transformed from a tropical greenhouse to the icy world of today.

Their new research reveals that the significant drop in global temperatures after the dinosaurs went extinct may have been caused by a significant decrease in calcium levels in the oceans.

An international team of experts led by the University of Southampton has found that calcium levels in the ocean have more than halved over the past 66 million years.

This study Proceedings of the National Academy of Sciences (PNAS), They showed that dramatic changes in calcium could have sucked carbon dioxide, a major greenhouse gas, out of the atmosphere and caused global cooling.

Lead author Dr David Evans, a marine and geoscientist from Southampton, said major changes in the chemical composition of seawater could be a key driver of climate change.

He added: “Our results show that at the beginning of the Cenozoic era, just after dinosaurs roamed the Earth, dissolved calcium concentrations were twice as high as they are today.”

“When these levels were high, the oceans behaved differently, acting to reduce carbon stocks in seawater and release carbon dioxide into the atmosphere.

“As those levels decrease, CO₂ was sucked out of the atmosphere, and the Earth’s temperature followed suit, lowering the climate by 15 to 20 degrees Celsius. ”

The Southampton researchers who supported the study worked with scientists from China, the United States, Israel, Denmark, Germany, Belgium and the Netherlands.

They built the most detailed record of ocean chemistry to date using the fossilized remains of tiny sea creatures dug out of seafloor sediments.

The chemical composition of this fossil, called a foraminifera, showed a close relationship between the amount of calcium in seawater and the level of carbon dioxide in the air.

Dr Evans said the research team used computer-generated models to show that high levels of calcium alter the amount of carbon “fixed” by marine organisms such as corals and plankton.

This allowed it to be stored in sediments on the ocean floor, effectively isolating it from the ocean and atmosphere.

Co-author Dr. Xiaoli Zhou from Tongji University in China added that as dissolved calcium concentrations have declined over millions of years, the way these organisms produce and bury calcium carbonate on the ocean floor has changed.

She added: “This process effectively takes carbon dioxide out of the atmosphere and traps it.

“This change may have altered the composition of the atmosphere, effectively rendering Earth’s thermostat inoperable.”

The experts also found that the decline in calcium roughly coincides with a slowdown in seafloor spreading, which is volcanic activity that continually creates new seafloor.

Co-author Yair Rosenthal, a professor at Rutgers University in the US, said that as the rate of production on the ocean floor slowed, the chemical exchange between rocks and seawater changed and dissolved calcium concentrations gradually decreased.

He added: “Seawater chemistry is usually seen as responding to other factors that drive climate change, rather than being caused by climate change itself.

“But our new evidence suggests that to understand the history of Earth’s climate, we need to focus on changes in seawater chemistry.

“Changes in these deep Earth processes may be the ultimate cause of many of the large climate changes that have occurred over geological time.”

read more www.pnas.org/doi/10.1073/pnas.2511781122.

end
552 words