The recent solar eclipse plunged a swath of the U.S. into two minutes of gloom, but it’s nothing compared to the years-long night that almost wiped out life on Earth 66 million years ago.
Planet-wide wildfires killed land-dwelling creatures like dinosaurs after a six-mile asteroid struck the Yucatan peninsula, kicking off one of Earth’s five known mass-extinctions.
But it was the long night that fell as 15,000 million tons of fine soot rose into the stratosphere, shutting down global photosynthesis for two years and destroying the ozone layer. The long night likely doomed the rest of the three-quarters of species that died.
Chuck Bardeen of the National Center for Atmospheric Research led the PNAS study, published this week.
“This would have had a great impact on life that might have survived the immediate effects of the impact, because there wouldn’t have been a primary food source,” Bardeen said. “So, plants wouldn’t have grown, and phytoplankton in the ocean would likely have died.”
The soot layer initially shielded the already-stressed survivors from the effects of the global ozone hole, but rain drove the particulates from the sky before the O3 layer could repair itself. This only deepened the disaster, Bardeen said.
“You start out with broiling the surface. Then you cool things down, precipitation goes away, it gets dark, you don’t have photosynthesis,” Bardeen said. “Then, as you start to warm back up and precipitation comes back, and maybe things start growing, then you get this burst of ultraviolet radiation, which could cause mutations and death.”
Dust, not soot, was the prime suspect initially investigated after physicist Luis Alvarez and his son, geologist Walter Alvarez, proposed in 1980 that a giant asteroid strike had killed the dinosaurs.
In more recent years, and using more advanced models, scientists have investigated the effects of other particulates, such as sulfates that might have erupted from volcanoes or from the impact itself.
“For a while, we have thought that soot was one of the things that went into the atmosphere from the impact, but recently there’s been a renewed interest in looking at it in climate models to understand what the climate effects of that soot would be,” said Bardeen.
The NCAR Community Earth System Model (CESM) is among the most sophisticated simulations ever to tackle the Cretaceous−Paleogene extinction. It incorporates oceanic, land and sea-ice effects, as well as chemistry and advanced microphysics.
Scientists will now apply the model to additional Cretaceous research and to simulating nuclear winter scenarios.