A Short History of Nearly Everything | Study Guide

Bill Bryson

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A Short History of Nearly Everything | Part 4, Chapter 13 : Dangerous Planet (Bang!) | Summary



Bryson begins the chapter with a discussion of the impact crater of the largest meteor to hit the mainland United States. The story of how the Manson, Iowa, crater was discovered begins in the early 1950s with Eugene Shoemaker. A young geologist, Shoemaker posited craters were formed from objects coming from space. Along with his colleagues, Shoemaker began looking for the remnants of pulverized asteroids, rocky objects that orbit in a belt between Mars and Jupiter.

At the same time, American geologist Walter Alvarez and his father, physicist Luis Alvarez, employed the help of chemist Frank Asaro to understand how the KT boundary, a thin geological layer found in sedimentary rock throughout the planet, had formed. KT stands for Cretaceous/Tertiary, two geological periods whose boundary marks the extinction of the dinosaurs 65 million years ago.

Asaro measured the amount of iridium, an element found far more commonly in space than in Earth's crust, in the KT boundary and found it was far higher than normal. Other places around the world also had greatly elevated levels of iridium. The Alvarezes concluded the deposit of iridium must have been formed by a massive impact. They quickly realized this impact could have caused the extinction of the dinosaurs, along with about half the other existing species at the time. Paleontologists were outraged by the theory, especially since the location of the impact site was still unknown. Shoemaker now entered the story and proposed the Manson crater in Iowa as the impact location, but it was determined to be too old. By 1991 researchers established the Chicxulub crater on the Yucatán Peninsula in Mexico was the site of the impact.

Bryson next provides a discussion about the likelihood of seeing an asteroid prior to impact. He notes there would likely be no warning until it was too late. Even if there was enough warning, it is likely there is nothing officials could do to stop an asteroid from colliding with Earth. Its devastation would be colossal. The temperature of the atmosphere, compressed by the asteroid's velocity, would rise to 10 times that of the sun. Everything within 150 miles not killed by heat would be killed by the impact blast, followed by a shock wave that would kill "every standing thing" within an area as large as the Midwest. Soot and ash in the air would block the sun for months or years. While not all impacts result in extinctions, there is no way to know what the exact results of such a large impact would be until they occur.


This chapter marks the first of a series discussing the potential for the destruction of the planet. People have known about meteorites and meteorite impacts for centuries. However, the discovery of the link between the KT boundary layer and a massive asteroid impact showed scientists the potential for future collisions of meteorites on Earth's surface.

By discussing the potential for the destruction of the planet, Bryson is able to convey a sense of amazement for the existence of life, a common theme throughout the book. Even in the face of mass extinctions, life always rebounds on this planet—so far. The extinction of the dinosaurs allowed for an explosion of mammalian forms of life. Bryson notes this is an important fact: "It isn't actually necessary to look to space for petrifying danger." Life needs to be hardy to survive on Earth as it deals with natural disasters, the topic of the next chapter.

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