Around 66 million years ago, a massive asteroid crashed into Earth. The Chicxulub impact left a giant crater, plunged the planet into a global winter, and led to the mass extinction of dinosaurs. New modeling suggests that the crucial part of all of this was the dust.
The theory that freezing temperatures were central to the extinction of dinosaurs is accepted. The mystery is what about the asteroid impact triggered the sudden change in climate. A new study lays the blame on silicate dust. As the space rock hit the Yucatan Peninsula in Mexico, the impact sent huge quantities of dust into the atmosphere.
The layer of dust around Earth was so thick that it blocked out the sunlight. This did lead to dramatic cooling, but its pivotal effect was on plants. No sunlight meant that plants across the planet could not carry out photosynthesis. Just 14 days after the asteroid strike, all photosynthesis had stopped. Modeling suggests that the world remained in this condition for 620 days — almost two years.
The location of the Chicxulub Crater. Photo:
The University of Texas at Austin/Jackson School of Geosciences
Plant die-off
The lack of photosynthesis killed plants at an alarming rate. It effectively wiped out the first level of almost every food chain on Earth. Only animals and plants that could hibernate had a chance to survive. Eventually, 75% of all species on Earth died out.
Four years after the impact, photosynthesis had returned to its original level. The dust remained in the atmosphere for a further 11 years and sustained the lengthy 15-year winter.
Previous studies have only considered the dust as a fairly coarse material, made up of sulfur and soot. The team began by analyzing dust from 66-million-year-old rocks that were 3,000km north of the asteroid crater. They contained much more fine dust than expected, and the atmospheric blanket lasted far longer than one made of soot and sulfur.
The study fills in another piece of the mass extinction puzzle. But more work needs to be done. We still have to understand the exact killing mechanism. And how were marine organisms able to survive?
Many scientists think that there will never be an identifiable single killing mechanism but rather a mix of deadly effects from the asteroid strike.
