When Galileo trained his telescope on the moon in 1609 and discovered perfectly circular craters dominating its topography, astronomers began to wonder how they formed. Several astronomers, such as Franz von Gruithuisen, a German in the early 19th century, proposed the impact of the asteroid as a cause. But most have rejected this theory based on a simple, supremely confusing fact: the craters of the moon are almost perfect circles. And, as anyone who threw a stone in the dirt can tell you, that’s not how an impact scar should look. Instead, the mark will be elongated, oval and disordered. (Gruithuisen probably did not help his cause, also claiming that he saw cows grazing on the grass of the moon in these craters.) More deceiving any theorists, astronomers could distinguish small mountains at the center of each depression. Thus, for 300 years most astronomers and physicists believed that (1) cows did not graze on the grasslands of the moon and (2) lunar volcanoes, rather than meteors, struck its face.
Then, in the early 1900s, astronomers such as the Russian Nikolai Morozov* began to observe new powerful explosives newly developed and made a rather amazing discovery: large explosions differ from rocks thrown in many ways, but the most awful – at least for the continued existence of our species – leaves circular craters regardless of their angle of impact. As Morozov wrote in 1909 after conducting a series of experiments, the impact of the asteroid “throws dust around in all directions, regardless of their translational motion, just like artillery grenades when they fall to free ground.”
Before the discovery of Morozov, astronomers were aware that asteroids could be devastating. “The fall of a car even ten miles in diameter … would have been enough to destroy the organic life of the earth,” wrote Nathan Shaler, dean of Lawrence Lawrence School of Science and a supporter of volcanic theory, in 1903. But most believed that this was a completely theoretical exercise, partly because, as Shaler remarked in his defense of the theory of lunar volcanism, the very existence of humanity proved that this kind of impact could not have taken place.
Morozov’s calculations changed that. Once you know the true origins of the scars on the moon, you don’t have to be an astronomer – or even a telescope – to come to the worrying conclusion that asteroids have apocalyptic potential and that their impact is inevitable.
Shaler was, in a way, rightly wrong. An asteroid almost the size he described made Earth impact and made erase the dominant species of the planet. Rather than destroying humans, he paved the way for evolution for a placenta-sized mammal to finally crawl, walk, and consider an apocalypse camping trip.
You might think so the survival of your cunning ancestor proves that a mammal with a brain bigger than you would have a reasonable chance. Unfortunately, the shrew had a number of friendly adaptations to the apocalypse that people have lost since then. Musarah could survive on insects, take care of the heat and have fur to keep warm in the ensuing frozen decade. You could replicate some of the survival strategies of the spree. You may be terrified and expand your diet. But evolution has robbed you of others, and opposable thumbs may not be enough to save you when that twinkling star enters the Earth’s atmosphere at 12.5 miles per second.
At the impact of this speed, the Earth’s atmosphere behaves like water. The smaller stones – called meteors – hit the atmosphere like pebbles in a pond; they decelerate rapidly at high altitudes, either burning in their air friction or decelerating at their terminal velocity at low altitudes of 164 mph. But the mountain-sized asteroid Chicxulub hits our atmosphere like a boulder in a pond. It maintains its speed until impact, plunging through the entire 60 miles of the atmosphere in less than three seconds. The asteroid screams over Central America, emitting a sound boom that reverberates on the continents.
It falls so fast that the air itself cannot escape. Under intense compression, the air heats up thousands of degrees almost instantly. Before it even reaches the asteroid, compressed and overheated air vaporizes much of the shallow sea that covers the Yucatán in the late Cretaceous. Milliseconds later, the rock is thrown through what is left and crashes into the bedrock at more than 10 miles per second. At that moment, several almost simultaneous processes occur.
First, the affecting meteor applies so much pressure to the ground and rock that it does not break or shatter, but instead flows like fluids. This radical effect actually makes it easier to visualize the formation of the crater, as the ripples of the earth almost exactly replicate the double splashing of a cannon balloon in a pool in the backyard. The initial spraying in all directions is followed by a delayed vertical explosion when the cavity created by the impactor returns to the surface.