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A new Rutgers-led study claims that a key theory attributing early climate evolution to the breakdown of Himalayan rocks might not explain cooling over the past 15 million years.
The study could help us to understand the causes of long-term climate change brought on by natural causes.
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Long-term climate change
The study, published in the journal Nature Geoscience, is focused on the long-term cooling that took place before recent global warming caused by emissions released into the atmosphere by humans.
"The findings of our study, if substantiated, raise more questions than they answered," senior author, Yair Rosenthal, said in a press release.
"If the cooling is not due to enhanced Himalayan rock weathering, then what processes have been overlooked?"
The leading hypothesis
For decades, the key theory for cooling over the past 15 million years was that the collision of the Indian and Asian continents, which caused the Himalayas to rise up, brought fresh rocks to the Earth's surface. These rocks were exposed to the elements, making them vulnerable to weathering that stored carbon dioxide.
While unconfirmed, this has been a leading hypothesis for years.
Lead author Weimin Si, a former Rutgers doctoral student now at Brown University, and Rosenthal have now challenged the hypothesis with their new study in which they examine deep-sea sediments rich with calcium carbonate.
Algae and climate change
For millennia, the weathering of rocks allowed them to capture carbon dioxide. Rivers then carried the Co2 to the ocean as dissolved inorganic carbon. This is then used by algae to build calcium carbonate shells.
When the algae die, they fall onto the seafloor, their skeletons lock carbon dioxide into the Earth and preventing it from going into the atmosphere.
If weathering increases, the hypothesis says, levels of calcium carbonate in the deep sea should also increase. However, after studying several deep-sea sediment cores from an international ocean drilling program, Si found that calcium carbonate in shells has, in fact, decreased significantly over 15 million years.
This suggests that rock weathering may not be responsible for the long-term climate cooling. Rosenthal's lab is further studying the evolution of calcium in the ocean in order to find out more about long-term climate change.