- Adriana Ocampo. "The asteroid that extinguished the dinosaurs helped humans appear"
- Evolution: Night until the extinction of dinosaurs
66 million years ago a light appeared in the sky. As the hours passed, that point in the sky - visible from the northern hemisphere - became increasingly large and bright, until the asteroid that caused it crashed on the Yucatan Peninsula, triggering a planetary catastrophe that marked the end of the Cretaceous period and that left for posterity a crater 28 kilometers deep and more 100 km in diameter. The impact caused tsunamis, triggered massive forest fires throughout the planet and threw such amount of smoke and sulfur into the atmosphere that blocked solar radiation, causing a period of global cooling that ended with three quarters of the fauna that inhabited the Earth. .
The cataclysm also meant the disappearance of the dinosaurs, who had reigned over the planet for about 180 million years. "Not everyone disappeared that same day, but many did," summarizes Sean Gulick, a researcher at the University of Texas Geophysics Institute (UTIG) who has spent years studying the region where the asteroid fell, "they burned and then they froze. " Gulick and his team have discovered the most direct remains of the event that changed the history of the planet among the sediments that fill the crater Chicxulub. A finding that allows them to reconstruct the first hours that followed the impact. An international team with the participation of the Astrobiology Center (CAB / CSIC-INTA) has collaborated in its analysis. In total, more than twenty scientists whose conclusions are published Monday in Proceedings of the National Academy of Sciences .
The geological set they describe offers the most detailed look of that day and includes remains of charcoal, rocks and minerals, deposited by the immense tsunami that flooded the area of impact. But researchers are even more interested in what is missing: sulfur. "Part of the rocks we have studied are ocean sediments that include sulfur-rich rocks such as anhydrite," Gulick explains. And yet, there is no trace of this element; an absence that supports the hypothesis that the impact of the asteroid vaporized those sulfur-rich minerals and released them into the atmosphere.
Climate catastrophe
Once in the air, sulfur wreaked havoc on the global climate, the cloud blocked the planet's solar radiation and caused global cooling. The researchers estimate that at least 325,000 million metric tons (325 Gt) of this substance were released at that time. "Climate models that had estimated only 100 Gt of sulfur suggest a global fall of 25 ° in average temperatures, which means that almost everyone froze for much of the year," says the researcher.
While the asteroid created total destruction in this region of North America, it was global climate change that caused the massive disappearance of the megafauna , killing dinosaurs and most of the planet's life, including plants and trees. Gulick defines it as a brief and localized hell , followed by global cooling. "The real killer had to come from the atmosphere," he explains, "the only way to achieve global mass extinction is an effect on an atmospheric scale."
Anatomy of an extinction
Of all the great extinctions, the Cretaceous-Tertiary is the best known and the most studied. The disappearance of dinosaurs opened the door to the diversification of a new class of vertebrates: mammals. In 1980 a geologist named Walter Álvarez and his father, nuclear physicist Luis Álvarez, discovered that the sediment layer corresponding chronologically to the passage between the Cretaceous and Cenozoic periods was marked by large amounts of iridium, an unusual element on Earth but abundant in asteroids. They proposed a revolutionary hypothesis: a huge impact would have caused the end of the Cretaceous megafauna.
His idea materialized in 1991, when it was discovered that a crater buried under kilometers of sediment in the Yucatan Peninsula met all the requirements perfectly: the geological dating, size and chemistry of the rocks coincided. Since then crater and the asteroid share a name, Chicxulub, in honor of a small nearby Mayan town. Scientists believe that most of the material that filled the Chicxulub in the hours that followed the impact was a direct result of the same impact, or was dragged by seawater into the resulting tsunami.
It is estimated that a layer 130 meters deep in the ground was deposited that day, an extraordinary accumulation of materials in geological terms. In particular the sediments trapped in 40 meters captured what was happening in the atmosphere at that precise moment, especially around the crater, and give clues about the global consequences that triggered the impact that annihilated 75% of life on the planet. " What we have managed to recover in the zero zone is a detailed record of the events of that day, " says Gulick who, in addition to the study, co-directed the drilling mission of the International Ocean Discovery Program (IODP) in situ in 2016 . "It tells us the impact process from the position of an eyewitness."
The researchers estimate that the asteroid hit the crust with the equivalent power of 10 billion atomic bombs like those used in World War II. The explosion burned trees and plants that were thousands of miles away and triggered a massive tsunami that reached the northern tip of the American continent. Inside the crater, researchers have found coal and chemical biomarkers associated with fungi just above layers of sand, proof that land sediments were deposited by resurgent waters. "The tsunami was able to reach the Mexican Central Table, about 800 km west, returning to the crater to place a layer with biomarker remains and even coal from forest fires on the ground."
An animal booty
This same year a PhD student from the University of Kansas named Robert DePalma surprised the scientific community with a finding in the PNAS magazine: a site that corresponds exactly to the boundary between the Cretaceous and the Tertiary. Located in North Dakota, more than 2,000 kilometers from the Chicxulub crater the place (baptized as Tanis, by the city in the first installment of the Indiana Jones saga), was next to an inland sea and presents a unique loot of fossils and sediments: dozens of animals and plants of the flora and fauna of that period, many of them unknown until now.
"DePalma's work analyzes the effects in a place far from the impact, where the dominant facts are the arrival of the seismic energy that caused the local landslides, a wave (or seiche) in the inland sea and the arrival of the rain of the remains that fell from the crater "explains Gulick. "But their results are totally consistent with our observations, although the difference is that we are looking directly at the zero zone where the effects are more extreme and more varied."
THIS WAS THE CLIMATE CATACLISM PRODUCED
The impact. 66 million years ago a 10 km asteroid. wide it fell into the sea in front of the current Yucatan Peninsula (Mexico), heating the air, generating a supersonic wave. It formed a crater of 28 km. deep and within a few minutes, he had thrown 25 billion metric tons of debris into the atmosphere.
The tsunamis. Giant tidal waves resulting from the impact spread across the Gulf of Mexico, destroying coastal areas, first throwing debris inland and then absorbing everything into the depths. The sea creatures were dragged inland by tsunamis and earthquakes, where they mixed and were buried with land creatures, trees and river animals.
Fires. The asteroid vaporized on impact and its components were mixed with remnants of the earth's crust. The result was an immense accumulation of incandescent material that rose in the direction of the sky before falling like a mountain of burning dust. Scientists believe that the atmosphere 2,500 km around the zero zone warmed as a result of that storm of debris, causing gigantic forest fires. Over time, airborne material to other areas of the planet caused massive fires in the Indian subcontinent.
Sulfur. The vaporization of the rocks at the point of impact released some 325,000 million metric tons of sulfur, which radically modified the planet's climate. Sulfur combined with water to form sulfuric acid, which then fell like acid rain, killing off the leaves of any surviving plant and nutrients from the soil.
Cooling. The resulting cloud of sulfur and DE fires hid the sun's rays, causing global cooling. Once the fires were extinguished, the Earth submerged in a period of cold. The two essential food chains on Earth, both at sea and on land, collapsed in that period.
Extinction of living beings. Experts estimate that around 75% of all living species became extinct as a result of the impact and climate change. When sunlight finally got through the cloud, the oceans were virtually empty and the Earth was covered with ashes. The layer of ash and soot that finally covered the Earth indicates that the fires consumed about 75% of the world's forests. Among the few survivors were some mammals that, freed from dinosaur competition, could evolve in a wide variety of ways.
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