Dino killer asteroid darkened Earth for 620 days, say scientists

Scientists continue to piece together the events surrounding the extinction of the dinosaurs.

The asteroid that wiped out the dinosaurs is well known, but there’s still questions about what happened after the asteroid hit the ground in the Yucatán Peninsula in Mexico.

A new study in Nature Geoscience has simulated the next steps, finding that fine dust might have contributed more to the extinction event than previously realised.

The team found that micrometre silicate dust could have stayed in the atmosphere for 15 years, which would have lowered average temperatures on the surface by 15 degrees Celsius.

This would have blocked photosynthesis for almost two years (or 620 days) post impact, and may have directly caused extinctions of dinosaurs and other groups that couldn’t adapt to the conditions.

Interestingly, the team’s models also suggest that the recovery would have been faster in the Southern Hemisphere, which also matches the records which show less extinctions in those areas.

“Simulated changes in photosynthetic active solar radiation support a dust-induced photosynthetic shut-down for almost 2 years post-impact,” the researchers write in their new paper.  

“We suggest that, together with additional cooling contributions from soot and sulphur, this is consistent with the catastrophic collapse of primary productivity in the aftermath of the Chicxulub impact.”

The Chicxulub crater and the story around it is almost baked into our collective consciousness. About 66 million years ago, a huge 10-kilometre-wide asteroid struck what is now the Yucatán Peninsula in Mexico.  This spelt the end for the Cretaceous, the non-avian dinosaurs who inhabited the world, and more than 75 percent of animal species on Earth.

The researchers suggest that after the asteroid struck the earth, there would have been three types of particles that would have been an issue – sulphur, soot and silicate dust.

They looked at the boundary between the epochs – Cretaceous and Paleogene or K-Pg – analysing grain sizes using laser diffraction.  

“Our palaeoclimate simulations indicate that this micrometric grain-size pattern results in an atmospheric residence time that is much longer (>2 times) compared with previously estimated nano-sized or coarse particles,” the researchers wrote.

“Our results highlight that the photosynthetic shut-down induced by the large volume of silicate dust with grain sizes between ~0.8 and 8.0 micrometres, together with additional effects of sulphur and soot, probably led to a disastrous collapse of primary productivity in land and ocean realms, steering the global mass extinction at the K-Pg boundary.”