Part 4, Chapter 14 Summary and Analysis

In 1971, Mike Voorhies discovered one of the most extraordinary fossil beds in North America. It was a mass grave for scores of rhinos, horses, saber-tooth deer, camels and turtles killed around 12 million years ago. In a remote corner of what is now Nebraska, the animals died from breathing abrasive ash spewed by a volcano. The ash covered a depth of 10 feet, 1,000 miles from its source. That same volcano is active today and is overdue for a major eruption.

Scientists understand much less about the inner core of the Earth than about space. That is partly because it is 3,959 miles from the surface of the Earth to the center. There are three layers: the crust, mantle and core.

The Earth's crust and outer mantle form the lithosphere. The lithosphere drifts on a layer of softer rock called the asthenosphere. This...