When we have a really awful, sad and fearsome day, we tend to think of it as uniquely terrible. In the moment, we are not cheered by reminders that things have been worse, though we may later gain some solace with that reflection.
There was one day that dwarfs all bad days by many orders of magnitude. In the common vernacular it was the “Worst. Day. Ever.” No people witnessed it, but its terror awes us even today.
This was the day, about 66 million years ago, when an asteroid the size of Mount Everest smashed into the Earth at about 45,000 mph. The effects were globally catastrophic, both instantly and later.
In a wonderful, long article in “The New Yorker,” Douglas Preston tells the story of a young paleontologist, Robert DePalma, who has been excavating a site in South Dakota where he believes he has found fossil evidence from the actual day of this cosmic impact.
Before the 1980s, we thought dinosaurs went extinct because they were slow and stupid, outwitted eventually by the small mammals that had scurried beneath their ponderous feet for tens of millions of years.
That all changed with the realization that a worldwide catastrophe had occurred at just the time the dinosaurs went extinct, along with 75 percent of other species. Evidence for this involved planetary deposits of iridium, rare on Earth but common in asteroids, and the discovery of the Chicxulub impact crater off the Yucatan coast of Mexico.
Since then, scientists have tried to model the physical and environmental devastation of this event. If you think of Earth as a living creature, one scientist said, it was shot by a bullet and nearly died.
The blast at impact was more than that of a billion atomic bombs. A huge plume of debris rose above the atmosphere, some of it escaping into the solar system, to Mars and the moons of Jupiter and Saturn.
Earth’s atmosphere was heated to 700 degrees for 1,500 miles around. About 70 percent of forests worldwide were set ablaze by red-hot ejecta. Huge tsunamis surged, including one that raged up the inland sea covering what is now Texas.
It was particularly bad luck that the asteroid hit limestone, throwing up acid that eventually rained down to destroy vegetation and change the chemical composition of the sea.
After the heat and shock of the blast, debris blocked out the sun for years, shutting down photosynthesis and throwing the planet into a deep chill. After that, the accumulated carbon dioxide from the impact and burning changed global climate once again, overheating the planet.
The oceans lost much of their oxygen, and marine populations plummeted. One scientist estimates that 99.999 percent of plants and animals died within a few years of the impact.
There is a worldwide geological formation called the KT boundary. (Some scientists now call it the KP boundary, but the old name endures.) It marks the end of the Cretaceous period and the onset of the Paleogene period.
You can see it at Trinidad Lake State Park in Colorado. Below the boundary is soft coal, the remnant of ancient swamps and forests. Above is arid sandstone.
No dinosaur fossils have ever been found above the KT boundary. DePalma believes he has found evidence laid down in the catastrophe of that day. Preston’s article is a detailed description of the evidence. Read it.
Reflecting on these events dispels lingering romantic ideas about the goodness of the natural world. We might recall the value of life itself, and its precariousness.