Earth was destroyed by a mass extinction that wiped out most of the species on the planet. After other mass extinctions, it took a long time for the planet to be repopulated and restore its diversity.
Scientists might have figured out why Earth didn't recover quickly. Radiolarians disappeared in the aftermath of the extinction. A type of clay formation that released carbon dioxide was caused by their absence. The release of carbon dioxide would have kept the atmosphere warm and the oceans acidic, which would have slowed the rebound of life.
Clément Bataille, a professor of Earth and environmental sciences at the University ofOttawa, told Live Science that these were extreme conditions that hadn't been seen on Earth for hundreds of millions of years.
It shows how much we don't know about the biogeochemical cycles and how they can be thrown out of balance very quickly.
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Bataille was a researcher in Xiao-Ming Liu's lab at the University of North Carolina at Chapel Hill. At the end of the Permian and the beginning of the Triassic, the researchers were trying to understand changes in Earth's climate. The extinction event that resulted in the death of almost everything was caused by a huge block of volcanoes known as the Siberia Traps beinglching out greenhouse gases.
The team wanted to study the process of chemical weathering, which happens when rocks on land break down and release calcium into the ocean. The carbonate rocks are formed by combining calcium and carbon dioxide. Chemical reactions happen quicker in warmer temperatures and more water means more erosion. When it's warmer and weathering is faster, more CO2 flows into the sea and gets locked up in ocean rocks, which helps to cool the climate. When the climate cools, weathering slows and less CO2 is locked up in ocean rocks, so things don't get too cold.
Reverse weathering is a process that can occur in the ocean. New clays are formed on the ocean floor when the mineral Silica is abundant. These clays release more CO2 than carbonate rocks.
Because planktonic organisms snatch it up to make their shells, reverse weathering doesn't happen a lot. Radiolarians kept reverse weathering to a minimum by taking up most of thesilica.
At the end of the Permian and the beginning of the Triassic, all of that might have changed. The radiolarians may have been snuffed out, as the rocks made of many radiolarians disappeared. The balance of the different types of molecule in the ocean rocks went awry.
They were studying the ratios of the elements. There are versions of elements with slightly different atomic weights because they have different numbers of neutrons in their nucleus. In reverse weathering, new clays are formed in different ratios because of their differing weights. The researchers found that the ocean had almost disappeared from the surface before the Great Dying and didn't come back to life for millions of years. This paints a picture of a world where the loss of radiolarians led to an ocean full of sand, which allowed reverse weathering to occur. The CO2 released by reverse weathering could have overwhelmed the CO2trapping chemical weathering that was happening at the time. Life would have been difficult under those circumstances.
Hana Jurikova said that this was the first direct evidence that reverse weathering was occurring. She wrote an editorial about the research in the journal Nature Geoscience.
It's kind of an elegant theory, but there's a lot more work to be done.
What killed the radiolarians is one of the many unanswered questions. The evidence shows that the reverse weathering began a few million years before the mass extinction. It is possible that conditions were becoming difficult for life before the eruptions.
"We've been excited about the mass extinction and trying to zoom in as much as we can, but maybe we have to zoom out."
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