Earth's biggest extinction event probably took the plants first
From: University of Nebraska-Lincoln
Published: Friday, February 1, 2019
Little life could withstand the cataclysm of the Earth known as the Great Death, but plants may have suffered their wrath long before many animals, new research led by the University of Nebraska-Lincoln says.
About 252 million years ago, with the continental crust of the planet crumbling into the supercontinent called Pangea, the volcanoes of present-day Siberia began to erupt. Extracting carbon and methane into the atmosphere for about 2 million years, the eruption helped extinguish about 96 percent of ocean life and 70 percent of terrestrial vertebrates – the largest extinction event in Earth's history.
However, the new study suggests that a by-product of the eruption – nickel – may have led the life of some Australian plants to extinction almost 400,000 years before most marine species died.
"This is great news," said lead author Christopher Fielding, a professor of earth science and the atmosphere. "People have hinted at this, but no one has ever defined it. Now we have a timeline."
The researchers came to the conclusion by studying the fossilized pollen, chemical composition and age of the rock, and sediment layers on the cliffs of south-eastern Australia. There they discovered surprisingly high concentrations of nickel in the mud rock of the Sydney Basin – which is surprising because there are no local sources of the element.
Tracy Frank, professor and president of Earth and atmospheric sciences, said the finding points to lava eruption through nickel deposits in Siberia. This volcanism could have turned nickel into an aerosol that crawled thousands of miles south before descending and poisoning much of the plant life there. Similar peaks in nickel were recorded in other parts of the world, she said.
"So it was a combination of circumstances," Fielding said. "And that's a recurring theme in all five major mass extinctions in Earth's history."
If true, the phenomenon may have triggered a host of other: herbivores dying for lack of plants, carnivores dying of a lack of herbivores and toxic sediments that eventually turned into seas that were already recovering from increased carbon dioxide, acidification and temperatures .
It allows us to see what's possible & # 39;
One of the three couples from the research team, Fielding and Frank also found evidence of another surprise. Much of the previous research on the Great Death – often conducted near the equator – revealed abrupt changes in coloration in the sediments deposited during this period.
Gray-to-red sediment changes generally indicate that ash and greenhouse gas ejection from volcanism has altered the world's climate in large respects, the researchers said. However, this red-gray gradient is much more gradual in the Sydney Basin, Fielding said, suggesting that its distance from the eruption initially helped protect it from the intense temperature and aridity rises found elsewhere.
Although the time scale and magnitude of the Great Death have exceeded the planet's current ecological crises, Frank said that the emerging similarities – especially the peaks of greenhouse gases and the continued disappearance of species – make it a worthwhile lesson to study.
"Looking at these events in Earth's history is useful because it allows us to see what is possible," she said. "How has the Earth system been disturbed in the past?" "What happened where?" "How fast were the changes?" "It gives us a basis for working – a context for what is happening now."
The researchers detailed their findings in the journal Communications of nature. Fielding and Frank created the study with Allen Tevyaw, a graduate student in geosciences in Nebraska; Stephen McLoughlin, Vivi Vajda and Chris Mays of the Swedish Museum of Natural History; Arne Winguth and Cornelia Winguth of the University of Texas at Arlington; Robert Nicoll of Geoscience Australia; Bocking Associates' Malcolm Bocking; and James Crowley of Boise State University.
The National Science Foundation and the Swedish Research Council funded the work of the team.
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