New Delhi , Jan. 13 : New computer simulations have shown that tiny droplets of sulphuric acid resulted in long-lasting cooling, which was a likely contributor to the death of land-living dinosaurs.
An additional kill mechanism might have been a vigorous mixing of the oceans, caused by the surface cooling, severely disturbing marine ecosystems.
Researchers from Potsdam Institute for Climate Impact Research in Germany reconstructed how tiny droplets of sulphuric acid formed high up in the air after the well-known impact of a large asteroid and blocking the sunlight for several years, had a profound influence on life on Earth.
Previous theories focused on the shorter-lived dust ejected by the impact.
"The big chill following the impact of the asteroid that formed the Chicxulub crater in Mexico is a turning point in Earth history," said lead study author Julia Brugger.
The study appears in the Geophysical Research Letters.
"We can now contribute new insights for understanding the much debated ultimate cause for the demise of the dinosaurs at the end of the Cretaceous era," Brugger added.
The team used a specific kind of computer simulation normally applied in different contexts, a climate model coupling atmosphere, ocean and sea ice.
They build on research showing that sulphur- bearing gases that evaporated from the violent asteroid impact on our planet's surface were the main factor for blocking the sunlight and cooling down Earth.
"It became cold, I mean, really cold," said Brugger.
The dinosaurs were used to living in a lush climate.
After the asteroid's impact, the annual average temperature was below freezing point for about three years.
Evidently, the ice caps expanded. Even in the tropics, annual mean temperatures went from 27 degrees to mere five degrees.
"The long-term cooling caused by the sulphate aerosols was much more important for the mass extinction than the dust that stays in the atmosphere for only a relatively short time. It was also more important than local events like the extreme heat close to the impact, wildfires or tsunamis," explained co-author Georg Feulner.
It took the climate about 30 years to recover, the scientists found.
Surface waters cooled down, thereby becoming denser and hence heavier.
While these cooler water masses sank into the depths, warmer water from deeper ocean layers rose to the surface, carrying nutrients that likely led to massive blooms of algae, the scientists argue.
It is conceivable that these algal blooms produced toxic substances, further affecting life at the coasts.
Yet in any case, marine ecosystems were severely shaken up and this likely contributed to the extinction of species in the oceans, like the ammonites.
The dinosaurs, until then the masters of the Earth, made space for the rise of the mammals, and eventually humankind.
The study of Earth's past also shows that efforts to study future threats by asteroids have more than just academic interest.