It was, to put it mildly, a bad day for Earth when an asteroid hit Mexico’s Yucatan Peninsula 66 million years ago and triggered a global catastrophe that wiped out about three-quarters of Earth’s species and ended the age of the dinosaurs.
The immediate consequences were forest fires, earthquakes, huge shock waves in the air and in the seas. But the death blow for many species was a potential climate disaster in the years to come, when clouds of debris darkened the sky and temperatures plummeted.
Scientists have recently discovered the powerful role that dust thrown into the atmosphere from an asteroid impact site can play in causing extinctions, choking the atmosphere and blocking the process of photosynthesis. They calculated that the total amount of dust is about 2,000 gigatons, which is 11 times heavier than Mount Everest.
The scientists conducted paleoclimate simulations based on sediment excavated at the Tanis paleontological site in North Dakota, which preserved evidence of conditions following the fatal impact, including an incredible amount of dust.
Simulations showed that this fine-grained dust can block photosynthesis for up to two years and remain in the atmosphere for 15 years – said scientist Jem Berk Senel from the Royal Observatory of Belgium, lead author of the study published in the journal “Nature Geoscience”.
Previous research has pointed to two other factors, sulfur released after the impact and soot from wildfires. But this study found that dust played a bigger role than previously thought. The dust, or silicate particles of about 0.8-8.0 micrometers in size, that made up the global cloud layer, originated from granite and gneiss, broken off in the powerful impact that created the Chicxulub crater in the Yucatan, 180 km wide and 20 km deep. Earth subsequently suffered a drop in surface temperature of about 15 degrees Celsius.
For years it was cold and dark – says the scientist and co-author of the study Philip Kleis.
Earth fell into winter, with a drop in global temperatures and a collapse in primary productivity, the processes that terrestrial and aquatic plants and other organisms use to produce food from inorganic sources, leading to a chain reaction of extinction. As plants died, herbivores starved, carnivores ran out of prey and disappeared. In marine areas, the disappearance of tiny phytoplankton caused the collapse of food chains.
– While the sulfur remained for about eight or nine years, the soot and silicate dust were in the atmosphere for about 15 years after the impact. Full recovery from the long winter took even longer, and temperature conditions returned to pre-impact levels after about 20 years, said Ozgur Karatekin, a scientist and co-author of the study at the Royal Observatory of Belgium.