4: Plate Tectonics- Evolution of the Ocean Floor
- Page ID
- 45474
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CC1 Density and Layering in Fluids: The Earth and all other planets are arranged in layers of different materials sorted by their density.
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CC2 Isostasy, Eustasy, and Sea Level: Earth’s crust floats on the plastic asthenosphere. Sections of crust rise and fall isostatically as temperature changes alter their density and as their mass loading changes due to melting or to the formation of ice stemming from climate changes. This causes sea level to change on the coast of that particular section of crust. Sea level can also change eustatically when the volume of water in the oceans increases or decreases due to changes in water temperature or changes in the amount of water in glaciers and ice caps on the continents. Eustatic sea level change takes place synchronously worldwide and much more quickly than isostatic sea level changes.
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CC3 Convection and Convection Cells: Fluids that are heated from below, such as Earth’s mantle, or ocean water, or the atmosphere, rise because their density is reduced. They continue to rise to higher levels until they are cooled sufficiently, at which time they become dense enough to sink back down. This convection process establishes convection cells in which the heated material rises in areas of upwelling, spreads out, cools, and then sinks at areas of downwelling.
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CC7 Radioactivity and Age Dating: Some elements have naturally occurring radioactive (parent) isotopes that decay at precisely known rates to become a different (daughter) isotope, which is often an isotope of another element. This decay process releases heat within the Earth’s interior. Measurement of the concentration ratio of the parent and daughter isotopes in a rock or other material can be used to calculate its age, but only if none of the parent or daughter isotopes have been gained or lost from the sample over time.
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CC11 Chaos: The nonlinear nature of many environmental interactions makes complex environmental systems behave in sometimes unpredictable ways. It also makes it possible for these changes to occur in rapid and unpredictable jumps from one set of conditions to a completely different set of conditions.
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CC14 Phototrophy, Light, and Nutrients: Chemosynthesis and phototrophy (which includes photosynthesis) are the processes by which simple chemical compounds are made into the organic compounds of living organisms. The oxygen in Earth’s atmosphere is present entirely as a result of photosynthesis.
The ocean floor has irregular and complex topographic features—including mountain ranges, plains, depressions, and plateaus—that resemble topographic features on land (Fig. 3-4). During human history, those features have remained essentially unchanged aside from local modifications due to erosion, sedimentation, volcanic eruptions, and coral reef formation. However, the human species has existed for only a very brief period of the planet’s history (Fig. 1-4). In the billions of years before humans appeared, the face of the Earth was reshaped a number of times