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Guide to Reading
Chapter 1 dealt with the long ago and far away, presenting theories about the origin and development of the Universe. Chapter 2 brings you into the present and much closer to home with an overview—and an inner view—of planet Earth. It starts miles high above Earth in the vacuum of interplanetary space, then zooms you down through Earth’s magnetic field, magnetosphere, and Van Allen radiation belts, pausing in the troposphere to comment on the obvious topography of Earth and the great amount of hydrosphere covering Earth’s surface. The journey continues, diving down below the ocean surface and progressing through Earth’s crust, mantle, and core.
Much of the chapter deals with the ocean bottom and inner earth, as preparation for plate tectonics theory, presented in Chapters 3 and 4. The author discusses Earth’s composition (organic chemicals, minerals, glasses, rocks, metals, melts, and volatiles) and layers (oceanic and continental crust, the Moho, oceanic and continental lithosphere, asthenosphere, upper mantle, transition zone, lower mantle, outer core, and inner core.)
Few humans have visited the ocean bottom, and no human has physically been more than 2 mi below Earth’s land surface. How do we know what it’s like inside the Earth? Your author describes scientists’ efforts to reach deep into Earth and discusses the various approaches and scientific reasoning that have provided answers to questions about composition, structure, and conditions within Earth. These include the use of clues obtained from measuring Earth’s density and shape and the study of earthquake (seismic) wave velocities, and meteorites.
There are lots of terms and many numbers involved in this survey of Earth. Try not to get mired down in lists of rock types or thickness of layers. Instead concentrate on the thought processes necessary to analyze something you can neither see nor touch and on the truly amazing world that exists under your feet. John Milton’s underworld of the 1600s and Jules Verne’s fanciful journey of the 1800s were tame compared to the real thing. They imagined exotic versions of environments on Earth’s surface, all places within the realm of human experience. The real interior of Earth is beyond any human’s experience. It’s a place of awesome pressures and temperatures, much closer than the stars but just as unreachable. Truth can certainly be stranger than fiction. |
