66 million years ago, a massive bombardment of pulverized rock particles, which occurred just after a major impact from an asteroid at least ten kilometers in diameter, fell on Earth, and vast amounts of dust engulfed the planet. blue in complete darkness for about two years. The global catastrophe would have produced widespread forest fires, volcanic eruptions, and raised layers of dust, blocking sunlight and halting photosynthesis. This would also have cooled the planet at a drastic speed. All this, contributing to the mass extinction that marked the end of the age of dinosaurs.
These are the details of how the climate could drastically change after the catastrophe, published in the journal Proceedings of the National Academy of Sciences . The study, led by the National Center for Atmospheric Research (NCAR) with the support of NASA and the University of Colorado Boulder, has developed a model of how the conditions of the Earth after the impact of the asteroid, rather than the impact itself on yes, they could have conditioned the end of the Cretaceous Period. Information that biologists and paleontologists can use to better understand why some species died after the disaster, especially in the oceans, while others survived.
Scientists estimate that more than three-quarters of all species on Earth, including all non-avian dinosaurs, disappeared at the boundary of the Cretaceous and Paleogene periods, an event known as the K / Pg boundary. Evidence shows that the extinction coincided in time with the collision of a sizable asteroid in what is now the Yucatan Peninsula. But even more important were the long-term consequences of the collision, which would have triggered earthquakes, tsunamis and, of course, volcanic eruptions.
Scientists also calculate that the force of the impact would have thrown a vaporized rock above the Earth’s surface, where it would have condensed into small dust particles, known as spherules . As the spherules fell back to Earth, they would have been heated by friction to temperatures high enough to ignite global fires and scorch the Earth’s surface. The remains of this thin layer of spherules can be found in geological records around the world.
“The extinction of many of the large animals on Earth could have been caused by the immediate consequences of the impact, but more animals that lived in the oceans or those that took refuge in underground tunnels could have survived , in addition to the mammals that, of In fact, they subsisted, “explains NCAR scientist Charles Bardeen, lead author of the study. “Our model captures what happened after the initial effects. We wanted to see the long-term consequences of the dust layer that we believe covered most of the planet for two years , and what the consequences might have been for the animals that they survived in the months after the disaster.
To do this, the researchers simulated the effect of the dust layer on the long-term global climate. It is estimated that the Earth was covered by fifteen million tons of dust.
A chain reaction
In the simulations, the dust rose higher and higher in the atmosphere, eventually forming a global barrier that blocked most of the sunlight reaching Earth. “In the first moments, the Earth would have been as dark as on a moonlit night, ” according to Toon.
As a consequence, photosynthesis would have been impossible for more than a year and a half , and many of the plants would have already been incinerated. But the darkness probably would have had its biggest impact on phytoplankton, which is basic in the oceanic food chain . The loss of these tiny organisms would have generated a chain reaction across the ocean, devastating many marine species.
In addition, in the simulations, the loss of sunlight caused a pronounced decrease in the average temperatures of the Earth’s surface, with a drop of 28 degrees Celsius on the land and 11 degrees Celsius on the oceans.
However, while the Earth’s surface cooled in the study settings, higher up in the stratosphere, it was much hotter when dust particles absorbed sunlight. High temperatures destroyed ozone and allowed large amounts of ozone to be stored. amounts of water vapor in the upper atmosphere. The water vapor, then, reacted chemically in the stratosphere to produce hydrogen compounds that led to more and more ozone destruction. The resulting ozone loss would have allowed harmful doses of ultraviolet light to reach the Earth’s surface, making life on it even more difficult.
Nothing lasts forever
An especially surprising finding that took place during the simulation: water in the form of vapor stored in the Earth’s atmosphere played an important role in the disappearance of the layer of dust that covered the Earth. When the dust began to come out of the stratosphere, the air began to cool. This cooling, in turn, caused the water vapor to condense into ice particles, which ended up with more and more dust particles, until the soot layer was completely diluted, after remaining two years covering the surface of the earth.
Image: NASA
References: On transient climate change at the Cretaceous − Paleogene boundary due to atmospheric soot injections. Charles G. Bardeena, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley. PNAS (2017).
