A Short History of Nearly Everything | Study Guide

Bill Bryson

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A Short History of Nearly Everything | Part 6, Chapter 27 : The Road to Us (Ice Time) | Summary



A volcanic eruption in Indonesia in 1815 threw ash and dust into the atmosphere, "obscuring the Sun's rays and causing the Earth to cool." As a result, crops failed and livestock died. Bryson uses the example to show how Earth and ecosystems are sensitive to changes in climate. There is clear evidence Earth's climate has not been very stable during the course of its history. The 18th-century Scottish geologist James Hutton was the first to argue for large-scale glaciation, the idea ice masses called glaciers had once moved over large land areas. Naturalists Jean de Charpentier and Karl Schimper helped the idea to gain traction. Schimper coined the term ice age in 1837 to describe a period during which ice covered enormous amounts of land.

However, there was no explanation for how ice ages could have occurred. In 1864 James Croll, a Scottish janitor at the time, first suggested past ice ages could have been caused by changes in Earth's orbit, from elliptical, or slightly oval, to nearly circular and back to elliptical. Croll was later recognized for his brilliance and given an academic position. In the early 1900s a Serbian academic named Milutin Milankovitch realized this process would be too simple. He said rhythmic changes in the tilt, pitch, and wobble in Earth's orbits around the sun would contribute to ice ages. However, his ideas were not accepted until after the 1950s because of problems in dating technology at the time. It turns out there are many factors contributing to the development of ice ages, and science still does not understand exactly why they occur. Less well understood, Bryson says, are interglacials. These are the "cycles of comparative balminess" within ice ages during which all meaningful human activity has taken place. Earth's current interglacial has lasted over 10,000 years.

There have been numerous ice ages in Earth's past. About 2.2 billion years ago there was a "massive freezing ... followed by a billion years or so of warmth." Then Earth experienced its worst bout of cold, ice, and glaciation in a period called Snowball Earth. Scientists suspect Earth's oceans might have frozen over solid. Some ocean probably remained exposed, however, because cyanobacteria survived, and they need light to photosynthesize. Volcanoes might have caused the melting that followed.

Approximately 40 million years ago, a series of relatively smaller ice ages began. Bryson describes the Wisconsian ice sheet, which covered "much of Europe and North America," was up to two miles thick, and moved about 400 feet a year. With it moved whole landmasses, including Long Island and Cape Cod.

The most recent, the Younger Dryas, occurred about 12,000 years or so ago and lasted over 1,000 years. Much of what science knows about these periods of glaciation is taken from ice cores that show Earth's history has "lurched violently between periods of warmth and brutal chill." It seems another ice age is due, because they've been happening with some regularity for the last 40 million years. Possible causes are disruptions of "the normal patterns of ocean circulation," but this is speculative.

Global warming will not save Earth from another ice age because it could increase cloud cover and cause even higher accumulations of snow. Finally, Bryson discusses how ice ages have also resulted in numerous benefits for life on Earth. They formed freshwater lakes such as the Great Lakes, for example, providing nutrition to hundreds of species.


Part 6 is called "The Road to Us." Bryson leads off with a description of ice ages to show how these climatic events have influenced Earth and its species. While scientists still do not fully understand why ice ages occur, they can see the benefits—such as the formation of soil and freshwater lakes—that allowed the human species to flourish.

Bryson devotes some discussion, seemingly off-topic, to the possible results of global warming. For example, if the ice sheets melted, sea levels would rise by 200 feet. His point is humans "live on a knife edge." There is no way to predict whether the future holds killing cold or heat with equally devastating potential. His discussion of the benefits of ice ages is a reminder they are not, as he says, bad news in the long run.

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