Almost everyone knows that 66 million years ago an asteroid fell to Earth, which seemed to lead to the death of the dinosaurs. However, this fall led to mysterious consequences. Where armies of trees grew, stretching their branches to the sky, as if fleeing from thickets of ferns and bushes that grabbed them by the roots, only charred trunks remained. Instead of the incessant hum of insects and the screams of giant dinosaurs, there was only the whistle of the wind piercing the silence. Darkness fell: blue, green, yellow and red, dancing in the sun, everything was burned out.
This is what happened when a giant asteroid ten kilometers wide hit our planet 66 million years ago.
“In minutes or even hours, the lush and lively world turned into a quiet and desolate world,” says Daniel Durda, planetary scientist at the Southwest Research Institute in Colorado. "Especially in the area of thousands of square kilometers around the impact site - everything was completely destroyed."
By piecing together the puzzle of this fall, scientists have mapped out the long-term effects of the impact. He claimed the lives of more than three-quarters of all species of animals and plants on Earth. The most significant victims were dinosaurs - but many of them survived in the form of birds.
But it turned out to be a much more difficult task to paint everything in detail, especially what followed the fall and what allowed some species to survive.
For the first time, they started talking about the fact that the dinosaurs were destroyed by an asteroid impact in 1980. At the time, this idea was controversial. Then in 1991, geologists discovered the site of the fall - a crater with a diameter of 180 kilometers on the Yucatan Peninsula in Mexico. The crater was named Chicxulub after the nearby town.
The crater was difficult to find because it is underground. The northern part was also far from the coast, buried under 600 meters of ocean sediments.
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In April 2016, scientists began drilling a kilometer down the sea side of the crater to extract 3-meter-long core samples. A team of scientists will analyze the recovered samples to reveal changes in the type of rock, tiny fossils, and perhaps even the DNA enclosed in the stone.
“We’ll likely find a barren ocean at ground zero immediately after the impact, and then maybe see life come back,” says Sean Galik of the University of Texas Institute of Geophysics, who is involved in drilling.
Some things could be learned without drilling a crater.
For example, given the size of the crater, scientists calculated how much energy would have been released on impact.
Using this information, Durda and David Kring of the Moon and Planets Institute in Texas modeled the exact details of the collision and predicted what chain of events might occur. Scientists were able to test this scenario with fossils and check how accurate the predictions are.
“All of these calculations were painstakingly done,” says paleobotanist Kirk Johnson, director of the Smithsonian National Museum of Natural History. "You can build a scenario in which you go from the moment of the fall, the last second of the Cretaceous period, and then step by step move through the minutes, hours, days, months and years after the event."
And these studies tell a disastrous story.
The asteroid pierced the sky at a speed 40 times the speed of sound, and crashed into the earth's crust. The result was an explosion of 100 trillion tons of TNT equivalent - seven billion times more powerful than the bomb dropped on Hiroshima.
The impact on the earth's crust sent shock waves in all directions. Tsunamis up to 300 meters high in the Gulf of Mexico. Ten-point earthquakes destroyed the coastline, and within a radius of thousands of kilometers, an explosion tore and scattered all trees. Finally, tons of stones fell from the sky and buried the rest of their lives.
“It was basically a 10-kilometer bullet,” Johnson says. - Incredible physics. An incredible explosion, incredible earthquakes, incredible tsunamis, and everything within a radius of several hundred kilometers is covered with stones the size of houses."
Yet these regional impacts did not in themselves cause a global mass extinction.
When the asteroid fell, it vaporized a large chunk of the earth's crust. Over the place of the fall, debris rose like a torch, flying into the sky. “There was a huge, expanding ball of plasma that went into the upper atmosphere, into space,” says Durda. The torch expanded west and east until it covered the entire Earth. Then, being gravitationally bound to the planet, it spilled back into the atmosphere.
As it cooled, it condensed into trillions of glass droplets a quarter-millimeter in diameter. They rushed to the surface of the Earth with great speed and heated the upper atmosphere so strongly in some places that fires broke out on the ground. “The powerful heat from the re-entering emission created a hot effect on the planet,” Johnson says. "Now you have a stove."
The soot from the fires, combined with the dust from the impact, blocked the light from the sun's rays and plunged the Earth into a long, dark, wintry darkness.
Over the next several months, tiny particles fell to the surface, hiding the entire planet in a layer of asteroid dust. Currently, paleontologists can see this layer, preserved in the fossil record. This is the Cretaceous-Paleogene boundary, a turning point in the history of our planet.
In 2015, Johnson walked 200 kilometers of the exposed Cretaceous-Paleogene layer in North Dakota in search of fossils. “If you look under the layer, you can see dinosaurs,” he says. "But if you look above, no dinosaurs."
In North America, before the Chicxulub strike, the fossils painted a picture of lush forests with rivers flowing between, and dense undergrowth of ferns, aquatic plants, and flowering shrubs.
The climate was warmer then than it is now. There were no ice caps at the poles, and some dinosaurs roamed the northern lands of Alaska and far to the south on the Seymour Islands of Antarctica.
“The world was as biologically rich and diverse as everything we see around us today,” says Durda. - But later, and especially near the place of the fall, the environment became similar to the moon. Deserted and barren."
Scientists deduced the consequences of the fall of the asteroid by studying the Cretaceous-Paleogene layer, which was found in 300 places around the world.
“Unlike any other geological process, the fall of an asteroid occurs instantly. All this has not been stretched over hundreds or tens of millions of years. It all happened instantly, says Johnson. "After we have identified the layer of debris in the impact crater of the asteroid, we can go lower and higher, compare what happened before and after."
Closer to the impact site, animals and plants died either from scorching temperatures, from wild winds, from earthquakes, tsunamis or boulders falling from the sky. Further, even on the other side of the globe, species suffered from a chain reaction like the lack of sunlight.
In regions where the living environment has not been destroyed by fires, temperatures have destroyed food for animals, and acid rain has spoiled water supplies. To make matters worse, the debris in the air has caused the Earth's surface to become as dark as in an unlit cave, ending photosynthesis and destroying food webs.
As the vegetation was gone, the herbivores had nothing to eat. If the herbivores die, the carnivores have nothing to eat. It became impossible to survive. Everything that did not burn out died of hunger.
The fossils show that nothing larger than the raccoon survived. Smaller creatures have a chance because there are usually more of them, they eat less and can reproduce and adapt faster.
Freshwater ecosystems, in principle, felt better than terrestrial ones. But in the ocean everything went to pieces, all food chains collapsed.
While the long winter stopped photosynthesis, its effects were greater in the hemisphere that entered the growing season. "If you are in early summer in the northern hemisphere, for example, and your lights are turned off during the growing season, problems arise."
The fossils indicate that North America and Europe were the best after this hell. This suggests that winter was beginning in the northern hemisphere when the asteroid fell.
But even in the hardest hit areas, life soon crawled back.
“Mass extinction is a double-edged sword. On one end: what killed life. At the second end: what abilities did plants and animals need to survive, develop and recover?"
The recovery took a long time. It took hundreds, if not thousands of years to restore ecosystems. Scientists estimate that it took three million years in the oceans for organic material to return to normal.
As in the aftermath of the wildfire today, ferns quickly colonized the burned areas. The ecosystems that escaped the invasion of ferns were dominated by thickets of algae and mosses.
In areas that have escaped the worst destruction, some species have survived to repopulate the planet. Sharks, crocodiles and some species of fish have survived in the oceans.
The disappearance of the dinosaurs meant that new ecological niches were opening up. “It was the migration of mammalian species into these empty ecological niches that led to the abundance of mammals that we see in the modern world,” says Durda.
When scientists drill the crater this spring, they will again be trying to get a clearer picture of how the crater formed and the impact of the fall on the climate.
“We can do better analysis from inside the crater,” Johnson says. “We’ll learn a lot about the distribution of energy and especially about what happens to the Earth when something of this size falls on it.”
In addition, scientists will look at the minerals and cracks in the rocks and try to understand what might have lived there. Drilling will help us understand how life was restored.
"Watching how life comes back, you can find answers to a couple of questions," says Galik. - Who came back first? What kind was it? When did evolutionary diversity appear and how quickly?"
Although many species and individual organisms died, other life forms began to thrive in their absence. This dual picture of disaster and opportunity has been repeated many times throughout the history of the Earth's falls.
In particular, it is likely that if the asteroid had not hit the Earth 66 million years ago, the course of evolution would have been completely different - and people might not have appeared. “Sometimes I say that Chicxulub crater became the crucible of human evolution,” says Kring.
He also suggested that the impacts of large asteroids may have helped give birth to life.
When the asteroid fell, the intense heat triggered intense hydrothermal activity in Chicxulub crater that could last for 100,000 years.
And she could allow thermophiles and hyperthermophiles - exotic single-celled organisms that thrive in hot, chemically enriched environments - to settle inside the crater. Drilling will test this idea.
Since its inception, the Earth has been regularly bombed. In 2000, Kring suggested that these impacts created underground hydrothermal systems like those that may have formed at Chicxulub crater.
These hot, chemically rich, humid places may have given rise to the first life forms. If so, then heat-resistant hyperthermophiles were the first forms of life on Earth.
ILYA KHEL