Chapter 1: The Earth in Context
Study Plan
When the Hubble Space Telescope looks into the night sky, it reveals a spectacle of disks and spirals of hazy light. Each of these is a distant galaxy, a cluster of as many as 300 billion stars.
Credit: R. Williams, the HDF Team, and NASA
Guide to Reading
If you've always thought that the study of Earth is limited to identifying rocks and minerals, you're in for some surprises, starting with this chapter. Geology claims as subject matter just about anything Earth related. It's a very eclectic subject (composed of a broad selection of topics from many different sources). With this in mind, begin reading Chapter 1, and note how it very logically starts at the beginning of everything-"everything" being, literally, the Universe.
For thousands of years humans have sought to understand the Universe they're part of-its beginnings, structure, functioning, and future. Today we term these studies cosmology. Many of the earliest ideas were fanciful, though there were also investigations of a more scientific nature. People asked the right questions, made careful observations of natural phenomena, used common sense and ingenuity, and came up with quite accurate answers to some basic yet profound questions. Human history and this chapter are both filled with many of these milestones of understanding. Included in this chapter are discussions of the following:
- the discovery that planets are wanderers, different from stars
- Ptolemy's belief in an Earth-centered Universe
- the opposing belief in a Sun-centered Universe
- the discovery of galaxies, including our own Milky Way
- Doppler's explanation of wavelengths and frequencies altered by moving sources
- the correlation between the Doppler effect and the red shift of the expanding Universe
- the big bang theory of the beginning of the Universe
- the realization that stars have beginnings, lifetimes, and deaths
- the realization that existing stars are of different ages, generations, sizes, temperatures, and densities
- the process of element formation in stars
- the development of our round Earth and our planetary system
- the origin of our Moon
The vastness of the Universe defies comprehension, so, as your author explains, scientists created special units like the light year to make the mathematics about it more manageable and frequently use analogies to help humans fathom its large-scale processes.
After reading all this, you may feel you've had a crash course in ancient astronomy. In a way, you have, but you also have established a firm foundation for your study of geology.
The chapter continues 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 this section deals with the ocean bottom and inner earth, as preparation for plate tectonics theory, presented in Chapter 2. 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 miles 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.
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