On Monday the moon passed directly between the sun and the Earth, sending towns in the path of totality into darkness for a maximum of two minutes. But 66 million years ago, after a great asteroid struck the world of the dinosaurs, the sun’s light was blotted out around the planet for an unbelievable two years.
That’s according to a study published Monday in the Proceedings of the National Academy of Sciences, by scientists at the National Center for Atmospheric Research and the University of Colorado at Boulder. The researchers used a computer model to simulate the aftermath of asteroid strike — especially ash and soot sent skyward by massive forest fires that would have raged around the world.
It’s hard to overstate the intensity with which the asteroid, at an estimated six miles in diameter, hit Earth. According to one recent study, the space rock would have blown clear through the planet’s crust and into the upper mantle, vaporising the asteroid itself and a large chunk of Earth as well.
The force triggered volcanoes, earthquakes, and tsunamis that rippled across the planet. The skies filled with red-hot chunks of rock that fell like rain to Earth, literally broiling the surface and setting off wildfires around the world.
The intensity of this immediate heat likely killed most of the large land-dwelling animals, too big to find shelter in from the firestorm. But the most deadly part of the event surely came after, when soot from the forest fires blacked out more than 99 percent of the sun’s light, killing plants on land and in the oceans and leaving Earth’s creatures with few sources of food, once the rotting carcasses of the fallen had been scavenged.
Land temperatures plunged by up to 50 degrees Fahrenheit, and ocean temperatures by 20 degrees. The sun didn’t substantially return for two years, and most of the planet remained in a deep freeze for three or four.
An estimated three-quarters of species on Earth simply died out, unable to feed themselves through this perilous time. Some small, rodent-like mammals made it through and went on to diversify into all of the mammalian life we see on this planet today. Some reptiles and amphibians made it through, including snakes, frogs, and crocodiles. Sea life fared best, although life was still tough in those first years when algae were scarce.
The only dinosaurs to survive were birds — birds with all of the bird-like features we ascribe to the animals today. They may have been better off than the rest in part thanks to their beaks, which can crack open seeds, which can store energy over many years.
It was a terrible time to be alive on Earth, although every creature here today has that tragedy to thank for their very existence. It was a world-changing event, one that dramatically shaped the course of life on this planet.
Abstract: Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous−Paleogene boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wildfires ignited after the impact of a 10-km-diameter asteroid on the Yucatán Peninsula 66 million y ago. Following injection into the atmosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injection of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth’s surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photosynthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.