When a six-mile-wide asteroid struck the Earth 66 million years ago, it left a massive impact crater over 100 miles wide, today called the Chicxulub crater in eastern Mexico. Since the late 20th century, the impact event has been triangulated as the decisive event triggering the Cretaceous–Paleogene extinction, which killed three-quarters of all life on the planet, bringing about the end of the era of the dinosaurs and the beginning of mammalian domination of our world.
However, the exact mechanisms by which the asteroid impact caused such mass death remain largely unknown, with some theories holding that rapid acidification of the seas combined with worldwide forest fires and volcanic events choked out most life in the years after the impact. A new study has found that the real killer was likely ultra-fine dust particles thrown into the atmosphere, blotting out the sun and choking the world’s plants.
Chicxulub Crater, Mexico
© Photo : Wikipedia
In the fossilized sediments of what at the time of the impact was a lake, scientists found something different than they expected. Where they thought they would find sulfur, and thus evidence of poisonous gases, or soot from fires, they instead found a layer of ultra-fine silicate powder. The particles were so tiny, around 0.8 to 8.0 micrometers, that they could have hung in the atmosphere for up to 15 years.
Ozgur Karatekin, a researcher at the Royal Observatory of Belgium and one of the co-authors of the study, said such a volume of dust particles in the atmosphere "totally shut down photosynthesis" in plants for at least a year, causing a "catastrophic collapse" of life.
“Photosynthesis shutting down for almost two years after impact caused severe challenges (for life),” said lead study author and planetary scientist Cem Berk Senel, a postdoctoral researcher at the Royal Observatory of Belgium. “It collapsed the food web, creating a chain reaction of extinctions.”
In addition, the dust would have reflected sunlight, triggering a dramatic cooling of the Earth’s climate by as much as 15 degrees Celsius - a phenomenon that once bore the sole blame for the dinosaurs’ extinction.
They concluded that the worst effects would have come immediately after the impact, which vaporized the seafloor of the Gulf of Mexico to create the silicate dust. After about two years, much of the dust would have settled and some photosynthesis would have begun again, but the damage by then would have already been done.
Sean Gulick, a geophysicist at the University of Texas at Austin who wasn’t involved in the research, told US media that by studying the Cretaceous–Paleogene extinction event 66 million years ago, we can better understand what scientists have come to call the threat of the Anthropocene Extinction, which may erase the human civilization.
"Maybe we can better predict our own mass extinction that we're probably in the middle of," Gulick said.