Dinosaurs met a hellish end as fiery brimstone rained down from the sky and broiled the Earth’s surface after a massive asteroid struck the planet.
The biblical horror continued with billions of tons of soot from the fires blotting out the sun and plunging the Earth into icy darkness for nearly two years, new research has shown.
In addition, large-scale
destruction of the protective ozone layer high in the atmosphere led to DNA-damaging levels of ultraviolet radiation.
By the end of the disaster, known as the K-Pg extinction, more than three quarters of species on Earth, including all the dinosaurs that did not evolve into birds, had been wiped out.
Scientists recreated the nightmarish aftermath of the meteor strike 66m years ago using powerful computer simulations and evidence from the estimated 15bn tons of fine soot left behind by the cataclysm.
The 10km-wide asteroid smashed into a shallow sea off Mexico’s Yucatan peninsular, triggering earthquakes, tsunamis, volcanic eruptions and, worst of all, a burning rain of incandescent rock particles that ignited raging global fires.
Soot from the fires swept up into the atmosphere by air currents blocked out 99% of the sun’s light for around 18 months, making every day as dark as a moonlit night.
During this time average temperatures plummeted by 28C on land and 20C in the oceans and surviving plant life deprived of photosynthesis perished.
Lead scientist Charles Bardeen, from the US National Center for Atmospheric Research, said: “The extinction of many of the large animals on land could have been caused by the immediate aftermath of the impact, but animals that lived in the oceans or those that could burrow underground or slip underwater temporarily could have survived.
“Our study picks up the story after the initial effects — after the earthquakes and the tsunamis and the broiling. We wanted to look at the long-term consequences of the amount of soot we think was created and what those consequences might have meant for the animals that were left.”
The soot produced by the fires was more destructive than the debris and sulphurous particles thrown up by the asteroid collision itself, the researchers believe.
The blazes were lit by small particles or “spherules” created by vaporised rock condensing high in the atmosphere. As they fell back to Earth, the spherules were heated by friction until they were hot enough to spark fires.
All over the planet, the brimstone rain set anything that could burn alight and poured sun-smothering soot into the sky.
Four years after the impact the amount of sunlight reaching the Earth was still just 10% of normal, the simulations showed. It took around five years for the soot to wash out of the atmosphere, but even then the planet’s woes were not over.
Another effect of the soot was to heat up higher levels of the atmosphere and destroy the ozone layer. Fifty kilometres above the Earth, temperatures soared by more than 200C.
For about a year after the end of the blackout, the planet was bathed in ultraviolet radiation at levels far higher than the amount needed to produce sunburn. The effect on life is unknown but the UV rays could have damaged DNA in sensitive species, said the researchers.
The study, published in the journal Proceedings of the National Academy of Sciences, raises the frightening prospect of what might happen to the Earth after a global nuclear war.
Dr Bardeen said: “The amount of soot created by nuclear warfare would be much less than we saw during the K-Pg extinction, but the soot would still alter
the climate in similar ways, cooling the surface and heating the upper atmosphere, with potentially devastating effects.”
© Irish Examiner Ltd. All rights reserved