The air quality this week is bad. Smoke from Canadian wildfires has turned the sky orange in Philadelphia. It has veiled the Statue of Liberty in Manhattan. In Detroit, which has dealt with some of the worst conditions in the country, the smoke has almost entirely blurred the city’s skyline. The eastern United States isn’t exactly accustomed to smoke days, which can prompt someone like me, from the wildfire-prone West, to brag about how they’ve seen far worse. But those smoke days are nothing compared with the ones 66 million years ago. If you want to talk about bad air quality, ask the dinosaurs.
The asteroid that spelled the beginning of their end struck the Earth at about 40,000 miles an hour, blasting a 112-mile-wide crater into Mexico’s Yucatán Peninsula. The explosion was so big that it punched a hole into the atmosphere, bringing “outer space down to the surface of the Earth,” Kirk Johnson, the director of the Smithsonian National Museum of Natural History, told me. The impact flung trillions of tons of debris into the sky, and much of it headed right into that yawning atmosphere and into Earth’s orbit. As the planet continued to rotate, “you basically got a global cloud of dust and debris that blocked sunlight from hitting the ground,” Johnson said. And it blocked virtually all of the sunlight—plunging the world into solar-eclipse-level darkness. Some hot debris fell back down from the atmosphere, and within minutes, wildfires were spreading. Enormous conflagrations combusted “all the biomass on the planet, not just some forests in Canada,” Johnson said—and with debris blocking the sun, those wildfires were “burning in a dark world.”
Given the worldwide fires, dinosaurs would have been trapped in a level of smoke far more intense than the kind of downwind exposure that the U.S. experienced this week, Brian Toon, a senior research scientist at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder, told me. Unfortunately—or maybe fortunately for them—many dinosaurs were not alive to experience this global-wildfire-pitch-black hellscape. The asteroid-impact event was a “massive, atomic-blast-scale thing, like 1 billion Hiroshimas of energy released,” Johnson said. The dinosaurs within about 1,000 miles of the impact site died “just by being exploded, basically,” he said—and given the magnitude of the blast, “if you were a human-sized animal standing anywhere on the planet at the surface, your survival of the first week is pretty unlikely.”
Other creatures perished during the ensuing climate mayhem. Within a week, maybe for months, the brightest day would have looked more like a moonlit night, Ken MacLeod, a geology professor at the University of Missouri, told me. The air wasn’t just smoky, he said; it was loaded with dust and gases. The gloom lasted for about two years, as particulates from the asteroid impact remained in the atmosphere and soot from wildfires added to them. The next couple of decades were “very low light, very difficult for photosynthesis to occur,” which led herbivores to starve, Brian Huber, a research geologist at the Smithsonian National Museum of Natural History, told me.
At what point would the atmosphere of this dark, foreign planet have settled into something like the haze hanging over Detroit today? No one was totally sure: “I would bet years, decades after,” Huber said. Johnson estimated that it would have been about a couple of years after impact; curators at New York City’s American Museum of Natural History found that 40 percent of sunlight was still blocked two years after the asteroid event, the museum told me. Although most soot and dust particles went away within a few years, sulfate aerosols continued to create “a global, orange-brown smog,” the dinosaur-extinction exhibit notes. According to the museum, it was only about four years after the asteroid arrived that full sunlight reappeared. The era in which the dinosaurs perished would be unrecognizable to a modern person. Compared with that, the air pollution Americans are facing right now, Huber said, “ain’t nothin’.”
Scientists know all of this in part because the sheer amount of charcoal and soot—millions and millions of tons of it—that fell to the ground left traces that are still detectable today. The asteroid itself also left a thin layer of debris made of meteorite and ancient parts of what we now call Mexico. You can touch it in Trinidad Lake State Park, in southern Colorado, Toon said—evidence from a time in this planet’s history when things looked pretty much as apocalyptic as one could imagine.
So, yes, the smoke this week is bad. The outdoor air quality is poor, and people should take precautions to limit the amount of it they’re breathing. And yet, there is something to be grateful for each day. And today, it is that we are not dinosaurs.
