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THE EARTH AND ITS SYSTEMS
Chapter 2 represents a new approach compared to earlier versions of the book. Although it incorporates some material from earlier versions, it utilizes a systems approach to introduce the student to the earth. The chapter covers internal systems first and then surface systems.
A short section on the origin of the solar system and planets leads into the earth’s early history and differentiation. This is a logical place to begin to discuss the earth’s internal systems, by describing heat flow, the earth’s magnetic field, gravity, and isostasy. These topics were previously covered in the middle of the book after chapters on minerals and rocks. The attempt in this revision was to have process precede dryer topics involving mineral and rock classification.
With a basic knowledge of solid earth geophysics, students are ready for plate tectonics. Plate boundaries and interactions are described in more detail than in previous editions. The predecessors to plate tectonics: continental drift and sea-floor spreading are covered so that students can follow the evolutionary steps leading to plate tectonics.
A new section on the earth’s surface systems follows, integrated from some topics that were dispersed throughout the book and topics that were not covered in previous editions. The major focus of this section is the interactions of atmospheric and oceanic circulation systems, concluding with a reminder that these systems play a critical role in climate and climate change, which was discussed in Chapter 1.
The introduction continues with a section on geologic time. Both relative and absolute time are discussed. The mathematical similarity in radioactive decay and population growth are pointed out and quantitative problems can be used to help students understand these concepts. The general types of rocks in the earth are introduced and a few other general concepts have been included. Hopefully, the student will now be ready and motivated to delve into earth materials in more detail.
2.1 Earth Systems
Comprehend that the earth’s internal and external systems are interrelated and both have major impacts on the human population.
2.2 The Earth, a Dynamic Planet
Recognize the relationship between the earth and the other planets in the solar system. Discuss the most important evolutionary events in the history of the earth and solar system.
2.3. Elements of the Earth’s Geophysical Characteristics Be able to state the importance of the earth’s heat flow, gravitational field, and magnetic field. Relate the earth’s heat flow to surface processes and large-scale landforms. Explain the relationship between crustal density and elevation. Discuss how the earth’s magnetic field was utilized to develop the theory of sea-floor spreading.
2.4 Plate Tectonics
Give an overview of the theory of plate tectonics and describe each type of plate boundary.
2.5 Atmospheric Circulation
Describe how unequal heating of the earth by the sun results in circulation of the atmosphere.
2.6 Oceanic Circulation
Describe how the oceanic circulation is divided into its various components and how oceanic circulation is related to climate and climate change.
2.7 Geologic Time
Comprehend the enormity of geologic time and the methods used for its measurement.
ANSWERS TO PROBLEMS
- The earth is composed primarily of elements of high boiling points such as iron, oxygen, silicon, and magnesium because of its position near the sun. Jupiter and Saturn were farther from the sun during accretion and contain a higher proportion of volatile elements.
- The earth partially melted, perhaps related to a large impact. As a result, the earth differentiated to form the core, mantle, and crust.
- The asthenosphere and lithosphere were recognized, and their importance in plate tectonics was realized.
- The earth’s magnetic field is related to circulating currents in the molten outer core of the earth. Patterns of paleomagnetism in oceanic crust indicate that the crust is formed by volcanism at mid-oceanic ridges and moves perpendicularly away from the ridges.
- Continental areas of high elevation have negative gravity anomalies (lower density) and ocean basins have positive gravity anomalies (higher density). Isostatic equilibrium refers to the tendency of crustal masses to “float” in the mantle at a level proportional to their density.
- Plate tectonics was a theory that integrated continental drift and sea-floor spreading along with many other forms of geophysical and geologic evidence indicating the existence and movement of lithospheric plates.
- Divergent boundaries occur over rising plumes in the asthenosphere. Rift valleys and mid-oceanic ridges occur above at the boundary. Convergent boundaries occur at plate collisions. Subduction zones and trenches are associated with this type of boundary. Transform boundaries are characterized by plates shearing past each other along vertical fractures.
- More solar energy is received at the equator than at the poles. Equatorial air rises and moves poleward and polar air moves toward the equator. Cells develop where air masses converge and diverge. Convergence aloft at about 30o north and south of the equator forms one cell boundary. Another occurs at about 60o north and south where divergence occurs aloft.
- Surface oceanic currents are driven by wind shear across the surface. They are broken into large gyres by land masses and the Coriolis effect.
- Deeper currents move by density gradients. This deep thermohaline circulation is a major
regulator of the earth’s climate.
- Catastrophism and neptunism are based upon biblical concepts of the earth’s origin.
- Steno formulated some of basic concepts of stratigraphy.
- Uniformitarianism holds that past geologic events operated under the same physical and chemical principles as modern processes. In its modern interpretation, geologic processes do not necessarily operate at the same rates and intensities throughout geologic time.
- Relative dating relies on physical characteristics such as cross-cutting relationships as well as fossil evidence.
- Absolute dating is limited by the occurrence and abundance of isotopes that can be used for dating.
- 21 x 10-4 yr-1
- 9091 yr