A Short History of Nearly Everything: Chapter 13 Summary & Analysis

In 1912, American water drillers are shocked to find that rocks in Manson Iowa don’t resemble the rocks elsewhere in the state. It turns out that 2.5 million years earlier, a mile-wide rock smashed into Manson Iowa, creating a crater 20 miles wide. Subsequent ice ages smoothed it over—erasing signs of a crater—but the impact obliterated the top layer of limestone that populated the rest of Iowa. In the early 1900s, most scientists believe that craters are the result of volcanoes and steam explosions within Earth. This is called into question, however, when a geologist named Eugene Shoemaker discovers anomalous substances in Barringer Crater, Arizona (subsequently renamed Meteor Crater) that suggest an impact from space. Shoemaker thus begins studying the asteroid belt with his colleague David Levy.

Asteroid research wanes in the 20th century when astronomers turn their attention to distant galaxies, so it isn’t until the early 2000s that a substantive—and growing—log of asteroids passing Earth’s orbit starts taking shape. Bryson asks the reader to imagine that Earth is the only car on a giant freeway (Earth’s orbit) and asteroids larger than 10 meters are wayward pedestrians—at any given moment, there would be over 100 million pedestrians crossing the freeway. Shockingly, about 2,000 asteroids large enough to destroy human life on Earth regularly cross Earth’s orbit. Two such near-misses were observed in 1991 and 1993. Some scientists even estimate Earth sees 2-3 such near misses per week—they’re just not visible to us until they’re too close.

In the 1970s, a young geologist named Walter Alvarez doing fieldwork in Italy becomes curious about a thin band of clay between two ancient layers of limestone. Now named the “KT boundary,” this layer marks the extinction of the dinosaurs. At the time, however, most scientists believe that dinosaurs died out gradually. Alvarez’s father, nuclear physicist Luis Alvarez, thinks that the clay came from space since space dust regularly settles on Earth—though not as much as in Walter Alvarez’s sample. They convince a colleague named Frank Asaro to test the clay, who realizes that it contains 300 times more iridium than normal.

Asaro and his colleague Helen Michel start testing samples from different places around the world and discover the iridium layer exists worldwide. The team concludes that Earth must have been struck by an asteroid that was pulverized into a giant dust cloud surrounding Earth, destroying the dinosaurs in an instant. Although the idea of asteroid impact killing the dinosaurs is already floating around (it’s hypothesized by several others as early as 1942), paleontologists are still shocked by Walter Alvarez’s evidence, as it goes against the more popular view of gradual extinction.

Walter Alvarez’s opponents dispute the claim, saying that there’s no evidence of an impact site. This prompts scientists to start hunting for one. Geologists Ray Anderson and Brian Witzke (along with Shoemaker) attribute Manson, Iowa’s soil anomalies to a meteor crash, and they think they’ve discovered the missing impact site buried deep under Manson Iowa. Unfortunately, the data eventually reveals that the impact in Manson happened 9 million years too early. The search continues, and in 1990 Alan Hildebrand learns about a strange ring formation in Mexico’s Yucatan Peninsula from a journalist. Hildebrand establishes this as the impact site, though the crater itself is buried under three kilometers of limestone.

After this, scientists are still slow to accept that the dinosaurs were killed by an asteroid—many argue that an 80-mile-wide asteroid couldn’t possibly trigger worldwide annihilation. Eventually, they decide to observe a comparably sized comet headed for Jupiter in 1994, and they’re shocked to that see it creates Earth-sized damage to Jupiter’s surface. Sadly, Shoemaker dies before seeing this, but the comet is named after him and his ashes are sent to the moon in a tribute to his research. With this insurmountable evidence, the scientific community finally accepts that the dinosaurs were, in fact, killed by the meteor that struck the Yucatan Peninsula.

Despite being the wrong crater, the Manson Crater becomes a hub for scientific analysis. Bryson asks Anderson and Witzke how much warning humans would have if a meteor (like the one that hit Manson) were to happen today, to which they reply “none”: it would be invisible until burning through the atmosphere, approximately one second before impact. Such a meteor would compress the air underneath it, making it grow 10 times hotter than the sun. Everything in that area would “crinkle and vanish like cellophane in a flame.” The meteor would vaporize upon impact, radiating a 150-mile wide shock wave at the speed of light.

People outside the impact zone would see blinding flash of light brighter than anything ever seen before, followed by a silent “rolling wave of darkness” moving faster than the speed of sound, flattening a 1000-mile wide area within minutes. People would be “sliced […] by a blizzard of flying objects.” After the initial shockwave, earthquakes, volcanoes, and tsunamis would likely be triggered, causing global devastation. Within an hour, Earth would be covered in a black cloud of debris raining burning rock that would set Earth on fire, destroying most life, after which soot in the atmosphere would blot out the sun for years (it took 10,000 years for Earth’s climate to normalize after the KT impact).

Bryson thinks that if there was a meteor headed our way, humans might try to blow it up. Unfortunately, no warhead or spacecraft could travel fast enough to reach the meteor before it would be too close. Even if we could blow it up, the pieces would still rain down on Earth in radioactive chunks. Asteroid hunter Tom Gehrels predicts we’d need several years’ advance notice to safely deal with such an asteroid, but we’d be unlikely to know it was coming until a few seconds before impact. Luckily, Witzke says that these sorts of things only happen once every million years or so. A handful of humans might even survive.