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| An international team of researchers discovered evidence that a mass extinction 260 million years ago was actually two events separated by 3 million years. Scientists say both likely were caused by volcanic eruptions. Credit: Margaret Weiner/UC Marketing + Brand |
Long before dinosaurs, Earth was dominated by animals that were in many ways
even more incredible.
Carnivores such as Titanophoneus, or "titanic murderer," stalked enormous
armored reptiles the size of buffalo.
Many of these animals died out in a mass extinction during the Capitanian
Age approximately 260 million years ago.
Now an international team of researchers says evidence suggests this mass
extinction was not a single event but two, separated by nearly 3 million
years. Both were caused by the same culprit: massive volcanic eruptions.
By studying uranium isotope profiles of marine samples collected in the
South China Sea, scientists identified two "pulses" in which the oceans
became deprived of life-giving oxygen.
In a study published in the journal Earth and Planetary Science Letters,
researchers say their analysis provides evidence that the oxygen-deprived
oceans precipitated two mass extinctions around 259 million and 262 million
years ago during the Middle Permian Period.
Looming climate disaster
By studying these ancient extinctions, researchers can better predict how
modern-day global warming could affect the ocean's food chain.
"We are studying the biocrisis in the Permian Period, but similar warming is
happening today because of human events," said Thomas Algeo, a study
co-author and University of Cincinnati professor of geosciences. "Humans are
mimicking the effects of volcanic eruptions as a consequence of the release
of carbon into the atmosphere."
The study was led by researcher Huyue Song at the China University of
Geosciences, a former postdoctoral researcher at UC.
"Today, we are facing several global change issues, including global
warming, ocean hypoxia, seawater acidification and biodiversity decline,
which are similar to the environmental changes during the Middle Permian
biological crisis interval," Song said.
Scientists have identified the five biggest mass extinctions, including the
most cataclysmic of all 252 million years ago called "the great dying" that
wiped out 90% of ocean life and 70% of land animals. This disaster, too, was
caused by massive volcanic activity that turned the seas into dead zones,
said Algeo.
"The Capitanian extinctions are not among the Big Five, but they are
significant," Algeo said.
How do volcanic eruptions lead to extinctions?
Algeo said massive eruptions create a brief period of cooling from ash in
the upper atmosphere reflecting sunlight, followed by much longer periods of
global warming. The release of massive volumes of greenhouse gases warmed
the oceans. The warm surface water did not allow dissolved oxygen to reach
lower depths, eventually destroying the food chain.
"The ocean is teetering on the edge of anoxia," he said of this absence of
oxygen. "Dissolved oxygen has to be taken up by the surface layer and
supplied to the deep ocean. But warmer water is lower density. When you
increase the density differential, you prevent any overturn and there's no
way to get dissolved oxygen into the deeper layers."
One way researchers identify these massive volcanic eruptions is by looking
for mercury in the sedimentary layers.
"Mercury has been shown to be a useful proxy for volcanic eruptions," Algeo
said. "Large volcanic eruptions spew mercury into the atmosphere that gets
carried around Earth and deposited in marine sediments."
Scientists say the volcanic eruptions that caused the great dying originated
in Siberia. The eruptions that caused the twin mass extinctions in the
Permian took place in southwest China in a place known as the Emeishan Large
Igneous Province.
Algeo said he would like to see if any terrestrial evidence supports the
conclusions derived from their study of ancient oceans. He is optimistic
that geology will unlock more mysteries about prehistoric life on Earth.
"Over the last 40 years we've made tremendous strides in understanding the
Earth's past," Algeo said. "It's partly because we have all these new tools
we can apply. And we have many more people working in this field than we had
a generation ago."
Researcher Song said the dual disasters in the Permian show the devastating
effects that global warming can have.
"We must pay attention to these environmental issues and prevent the sixth
mass extinction," he said.
Reference:
Huyue Song et al, Global oceanic anoxia linked with the Capitanian (Middle
Permian) marine mass extinction, Earth and Planetary Science Letters (2023).
DOI: 10.1016/j.epsl.2023.118128
Tags:
Planet and Environment