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Unformatted text preview: Chapter 7 Earth and the Terrestrial Worlds 227 summary of key concepts 7.1 Earth as a Planet • Why is Earth geologically active? Internal heat drives geological activity, and Earth retains internal heat because of its relatively large size for a terrestrial world. This heat causes mantle convection and keeps Earth’s lithosphere thin, ensuring active surface geology. It also keeps part of Earth’s core melted, and circulation of this molten metal creates Earth’s magnetic field. • What processes shape Earth’s surface? The four major geological processes are impact cratering , volcanism , tectonics , and erosion . Earth has experienced many impacts, but most craters have been erased by other processes. We owe the existence of our atmosphere and oceans to volcanic outgassing . A special type of tectonics— plate tectonics —shapes much of Earth’s surface. Ice, water, and wind drive rampant erosion on our planet. • How does Earth’s atmosphere affect the planet? Two crucial effects are (1) protecting the surface from danger- ous solar radiation—ultraviolet is absorbed by ozone and X rays are ab- sorbed high in the atmosphere—and (2) the greenhouse effect , without which the surface temperature would be below freezing. 7.2 The Moon and Mercury: Geologically Dead • Was there ever geological activity on the Moon or Mercury? Both the Moon and Mercury had some volcanism and tecton- ics when they were young. However, because of their small sizes, their interiors long ago cooled too much for ongoing geo- logical activity. 7.3 Mars: A Victim of Planetary Freeze-Drying • What geological features tell us that water once flowed on Mars? Dry riverbeds, eroded craters, and chemical analysis of Martian rocks all show that water once flowed on Mars, though any periods of rainfall seem to have ended at least 3 billion years ago. Mars today still has water ice underground and in its polar caps and could possibly have pockets of underground liquid water....
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This note was uploaded on 08/16/2011 for the course AST 2002 taught by Professor Britt during the Spring '08 term at University of Central Florida.
- Spring '08