On the last day of the Cretaceous period, a giant meteorite about 12 kilometers in diameter hit the Yucatan Peninsula in Mexico, changing the history of the earth’s life.
Now, 66 million years later, scientists are using supercomputers to recreate the world of the time according to many scenarios. The latest research on how life on Earth responded to dramatic changes in the environment, the real cause of the extinction of dinosaurs excepting birds, was published in the Journal of the National Academy of Sciences (PNAS) dated June 29.
The giant meteorite created a crater, nearly 200 kilometers in diameter, spreading huge amounts of gas, soot, and ash into the atmosphere. The sky was covered with darkness, a huge tsunami tore the sea, and the fire’s hands rose and burned down the surroundings. A few years later, the temperature dropped by more than 30 degrees Celsius, and a long, cold winter of the collision came. As a result, it is thought that more than three-quarters of life on earth was killed.
“It’s like Dante’s ‘Hell’ on Earth,” said Alfio Alessandro Kilenza, a researcher at University College London, who led the study.
Around the same time as this giant meteorite impact, known as the Chikshurub collision, large-scale volcanic groups erupted in places in what is now southern India. The volcano, known as the Deccan Trap, emitted lava and massive greenhouse gases of more than 800,000 cubic kilometers. For this reason, scientists have been discussing whether the cause of the mass extinction is a meteorite impact or a volcanic eruption for a long time. The majority of the theory of meteorite impact were large, but it was not well understood how much the volcanic eruption had affected it.
In this study, Kienza and colleagues re-create the ancient Earth’s climate by adjusting climatic conditions, assuming a variety of mass extinction scenarios. From there, it was concluded that only the meteorite impact was the cause that the earth where dinosaurs other than birds could not live. The volcanoes of the Deccan Trap were said to have made the earth a better place to live than to make it a place that was not suitable for life.
“I think this study will bury the theory that the Deccan trap has resulted in a mass extinction,” said Anjali Goswami, a paleontologist at the Natural History Museum in London. She is not involved in this study.
Today’s scientists want to figure out how to respond to organisms that have been driven into harsh environments in a short period of time by unraveling the mass extinction of the end of the Cretaceous period. “What do living things do when the foot is suddenly scooped down? We can get a hint to solve that,” said Pincheri Hal, a paleontologist at Yale University who is well versed in the extinction of dinosaurs.
But if scientists don’t agree on the cause of extinction, they can’t say they really understood mass extinction.
Studies over the past decade have shown that decan traps erupted multiple times in about 700,000 years. The question is how it was involved in mass extinction.
In the history of the earth, there have been five mass extinctions, especially on a large scale. Twice, it is caused by extreme warming caused by carbon dioxide emitted by volcanic activity. The 252 million-year-old Permian and Triassic mass extinctions, the largest mass extinction in history, were one of them, when volcanoes erupted in what is now Siberia, killing 96 percent of marine life and about three-quarters of the terrestrial species.
The Deccan Trap may have had two major effects on life 66 million years ago. One is that in the short term, sulfur dioxide emitted by volcanoes may have lowered temperatures, rain acid rain, and disrupted the sea and extensive chemical cycles. In the long run, a large amount of co2 produced by volcanoes could have led to global warming, draining global ecosystems.
In a paper published in 2019, two attempts were made to determine the age of the decan trap’s largest eruption. There was a gap of tens of thousands of years in the result. One is that it may have affected extinction before the meteorite impact. The other is a little after the collision, which is not related to extinction.
To recreate mass extinction, Kienza, and Alexander Vansworth, a climatologist at the University of Bristol, created a 66 million-year-old climate model of the earth. Simulations were performed on 14 different scenarios, including meteorite impacts, Deccan trap eruptions, and a combination of the two. CO 2 concentration is assumed to be up to 1680ppm, which hits about 4 times the current from 560 ppm, sunlight is assumed to be 20% dark from 5% is cut off by dust after the collision.
In some scenarios, 100 times the ash and aerosols of the 1991 eruption of Pinatubo volcano were discharged, and short-term cooling caused by the Chikshurube collision was also simulated. In order to track the effects of dinosaurs, the dinosaur habitats of the time were also mapped based on climate data at the time and where dinosaur fossils were found.
As a result, all models showed that the Deccan trap did not affect the extinction of dinosaurs. Long-term global warming by volcanoes means that dinosaurs were not extinct. The dinosaur ecosystem was not wiped out in a scenario where the sunlight was extremely blocked by the effects of the Deccan trap. On the other hand, the scenario of the meteorite impact was terrible. In some places, the average land temperature dropped from above 20°C to below freezing, with precipitation down from 85% to 95%. The Chikshurub collision blocked more than 15 percent of the sunlight, and there was no place for non-bird dinosaurs to live. (Reference article: “Dinosaur extinction, why did only birds survive?”
Looking at this data, Mr. Goswami said: “It’s natural that there are extinct things. Or rather, it’s more surprising that everything didn’t become extinct.”
The research team’s model also revealed unexpected facts. In fact, the Deccan Trap may have contributed to the recovery of life. It is said that the co2 emissions of the volcano have softened the severity of winter.
“It’s a big backlash,” Hal says. “No one has thought that the impact of the collision was reduced because of the volcano. I never really thought of it.”
Recent studies have shown that decan traps are more likely to have erupted little by hundreds of thousands of years than suddenly erupting and hitting global ecosystems. In November 2019, a group led by Mr. Hull discovered the rapid acidification of the Earth’s oceans in the tens of thousands of years after Chikshurube. This is likely to be the effect of acid rain after the collision. However, for about 100,000 years before the collision, the pH level of the sea was stable, even if the Deccan trap had already erupted.
Hal later found that global temperatures gradually rose about 2 degrees Celsius after a gradual rise in the 300,000 years before the meteorite impact. This indicates that CO2 levels have increased or decreased, but it is not extreme enough to threaten the survival of dinosaurs.
In addition, from India, where the volcano was active, clues have been found to indicate that the Deccan Trap has encouraged the recovery of life. In October 2019, Palaeontologist Tyler Lyson and others at the Denver Museum of Natural Sciences discovered several locations in the Rocky Mountains that recorded North American flora and fauna after a meteorite impact.
Lyson’s team found that the diversity of mammals and plants gradually increased as global warming progressed mildly after 100,000 years after the collision, even though there were few species in the ecosystem. This coincides with the time when the Deccan trap is thought to have emitted CO2.
Lyson says. “Recent research has raised interesting questions about whether the Deccan Trap is the creator or the vandal.”