by At the end of the Permian period 252 million years ago, the Earth was devastated by a mass extinction that wiped out more than 90% of species on the planet. Unlike other mass extinctions, the recovery from the “Great Dying” was slow: It took TK millions of years to repopulate the planet and restore its diversity.
Now, scientists might have figured out what delayed Earth’s recovery. A group of tiny marine organisms called radiolarians went extinct after the extinction. Their absence radically changed marine geochemistry, allowing a type of clay formation that released carbon dioxide. This release of carbon dioxide would have kept the atmosphere warm and the oceans acidic, thus slowing the recovery of life, the scientists explained in a paper published Oct. 3 in the journal Geoscience of nature (opens in new tab).
These were extreme conditions not seen on Earth for hundreds of millions of years, before the advent of widespread life, said study co-author Clément Bataille, now a professor of Earth and Environmental Sciences at the University of Ottawa in Canada. Live Science.
“It just shows how much we don’t know about these biogeochemical cycles and how a small change can really throw the system out of balance very quickly,” Bataille said.
An unfriendly Earth
Bataille worked on the research as a postdoctoral fellow in the lab of Xiao-Ming Liu, a geochemist at the University of North Carolina at Chapel Hill. Researchers were trying to understand changes in Earth’s climate at the end of the Permian (298.9 million to 251.9 million years ago) and the beginning of the Triassic (251.9 million to 201.3 million years ago). At that time, all the continents were united in a huge landmass called Pangeaand a huge block of volcano The so-called Siberian Traps fueled global warming greenhouse gaseslikely contributing to the extinction event that resulted in the death of almost everything.
The team wanted to study a process called chemical weathering – when rocks on land break down and release calcium, which erodes into the oceans. There, calcium combines with carbon dioxide (CO2) to form carbonate rocks. The warmer the climate, the faster corrosion occurs because chemical reactions occur faster at higher temperatures and more water flow means more corrosion. This creates a feedback loop that keeps global temperatures in check, Bataille said: When it’s warmer and weathering is faster, more CO2 flows into the sea and gets trapped in ocean rocks, helping to cool the climate. When the climate cools, weathering slows down and less CO2 is trapped in the ocean rocks, preventing things from getting too cold.
But there is another process that can happen in the ocean, called reverse erosion. This happens when the mineral silica is abundant and forms new clays on the ocean floor. During reverse weathering, these clays release more CO2 than the carbonate rocks can capture.
Silica isn’t abundant in today’s oceans because tiny planktonic organisms grab it to make their shells, so reverse erosion doesn’t happen much. Similarly, in the Permian, microscopic organisms called radiolarians took up almost all of the silica, thus keeping reverse weathering to a minimum.
A sudden shift
All this may have changed, however, at the end of the Permian and the beginning of the Triassic. At this point, silica-rich rocks from countless radiation shells disappeared, indicating that the radiolarians may have died out. At the same time, the balance of certain variant molecules in the ocean rocks was disrupted, Bataille, Liu and their colleagues found.
The researchers were studying lithium isotope ratios. Isotopes are versions of an element with a slightly different atomic weight than usual because they have a different number of neutrons in their nuclei. Because of their different weights, different lithium isotopes are taken up in different proportions when new clays are formed, which occurs in reverse erosion. The researchers found that some lithium isotopes essentially disappeared from the ocean just before the Great Dying and were not recovered for about 5 million years in the Triassic. This paints a picture of a world where the loss of radiolarian led to an ocean full of silica, thereby allowing reverse erosion to occur, Bataille said. The CO2 released by reverse erosion could have overwhelmed the CO2-trapping chemical erosion occurring at the time and, in turn, kept the climate too humid. Under such conditions, life would have been difficult.
This is the first direct evidence that reverse weathering was occurring at this time, said Hana Jurikova, a marine biogeochemist at the University of St. Andrews in Scotland. Jurikova did not participate in the research, but wrote one editorial accompanying the newspaper (opens in new tab) in the journal Nature Geoscience.
“There’s obviously a lot more work to be done,” Jurikova told Live Science, “but it’s an elegant theory.”
Among the questions that have yet to be answered are, what killed the radio amateurs? The evidence suggests that reverse erosion began a few million years before the mass extinction, Jurikova said, suggesting that perhaps these microorganisms were already struggling before the Siberian Traps did their worst. Perhaps conditions were becoming life-challenging even before the life-extinguishing volcanic eruptions.
“Traditionally we’ve been very excited about mass extinction and trying to zoom in as much as we can,” Jurikova said, “but maybe we’re finding that we have to zoom out.”
