The massive asteroid strike that wiped out dinosaurs some 66 million years ago would have plunged the Earth into darkness for nearly two years, a study has found. The asteroid triggered global wildfires that lofted into the air tremendous amounts of soot. This would have shut down photosynthesis, drastically cooled the planet, and contributed to the mass extinction that marked the end of the age of dinosaurs. The study, led by researchers at the US National Center for Atmospheric Research (NCAR), used a computer model to paint a rich picture of how Earth’s conditions might have looked at the end of the Cretaceous Period. The findings, published in the journal Proceedings of the National Academy of Sciences, may help better understand why some species died, especially in the oceans, while others survived. Scientists estimate that more than three-quarters of all species on Earth, including all non-avian dinosaurs, disappeared at the boundary of the Cretaceous-Paleogene periods, an event known as the K-Pg extinction. Evidence shows that the extinction occurred at the same time that a large asteroid hit Earth in what is now the Yucatan Peninsula. The collision would have triggered earthquakes, tsunamis, and even volcanic eruptions. Scientists also calculate that the force of the impact would have launched vaporized rock high above Earth’s surface, where it would have condensed into small particles known as spherules. As the spherules fell back to Earth, they would have been heated by friction to temperatures high enough to spark global fires and broil Earth’s surface. A thin layer of spherules can be found worldwide in the geologic record.
“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,” said NCAR scientist Charles Bardeen, who led the study. “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,” said Bardeen. Researchers used the NCAR-based Community Earth System Model (CESM) to simulate the effect of the soot on global climate going forward. In the simulations, soot heated by the Sun was lofted higher and higher into the atmosphere, eventually forming a global barrier that blocked the vast majority of sunlight from reaching Earth’s surface. While the skies would have gradually brightened, photosynthesis would have been impossible for more than a year and a half, according to the simulations.
Since many of the plants on land would have already been incinerated in the fires, the darkness would likely have had its greatest impact on phytoplankton, which underpin the ocean food chain. The loss of these tiny organisms would have had a ripple effect through the ocean, eventually devastating many species of marine life.