In Chapter 2 "A Cast of Continents," Lange describes the positions of the continents at different times, and how land bridges between Europe and North America and between North America and South America allowed animals to travel between these landmasses. Diagrams reconstructing the positions of the continents visually illustrate this discussion. In a lengthy sidebar, Lange presents the evidence for the existence of Pangaea and the positions of the continents through time.
In Chapter 3 "The Pleistocene Epoch," Lange gets into the hard scientific evidence that we have for the existence of several "ice ages" in Earth's history. While Swiss geologist and physicist Horace Benedict de Saussure noted in 1787 the presence of "erratics" (large, glacially transported boulders of rock types that do not match the rock types in the area), he believed that these boulders were transported by the Noachian flood. It was not until 1837 that Swiss zoologist Louis Agassiz proposed that an ice sheet had spread from the North Pole to the Alps, and the existence of a catastrophic climate change. Lange discusses using oxygen-isotope values, strandlines (wave-cut beach terraces), glacial deposits, and crustal depression and rebound to study past glaciations. A lengthy sidebar discusses Pleistocene animal communities.
In Chapter 4 "Why the Ice Ages?" Lange discusses some hypotheses for the cause(s) of the Ice Ages. He discusses external causes, such as variations in solar radiation, Milankovitch cycles (caused by changes in Earth's orbital eccentricity, variable tilt of the Earth's axis, and precession of the Earth's axis), interplanetary dust. Lange then discusses Earth-related causes, such as the changing configurations of continental landmasses, changes in the atmosphere's composition, volcanism, absence of glaciers in the Arctic, Heinrich events (huge discharges of icebergs into the North Atlantic ocean), presence of high-elevation landmasses, and human activities.
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