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Transcript
The EARTH: Its HOT Inside! Geoscience 10: Geology of The National Parks Unit 2 The EARTH: Its HOT Inside! The deeper a mine or oil well is, the hotter it is at the bottom; volcanoes bring up heat from below; Earth’s heat made mostly by decay of natural radioactive atoms in rocks; How materials (and people!) behave depends on what they are (iron, silica, etc.) and on the conditions they are placed in (heat, pressure); Geoscience 10: Geology of The National Parks Unit 2 EARTH: Layered by Composition & Behavior Iron core, mantle with silica added to iron, ocean crust with more silica, continental crust with still more silica (way more complex than this, but this is a start)--going up, each layer less dense and floats on layers below; Core has solid inner part (higher pressure squeezes to solid) and liquid outer part; Crust plus upper mantle (called lithosphere) tend to break not flow; deeper in mantle tends to flow not break (asthenosphere, plus other names and layers we won’t worry about) (hot solids can flow--think of chocolate bar in your pocket, or blacksmith making horseshoes); Mantle and crust solid, but with a little melt in few places. Geoscience 10: Geology of The National Parks Unit 2 CONVECTION: Moving the Mantle’s Heat Heating causes expansion & rising, cooling causes contraction & sinking; together form convection cells (in spaghetti pots on stove, and in soft part of Earth’s mantle) Lithosphere broken into a few big plates that raft around on the convection cells like scum on a spaghetti pot; Where the lithospheric plates are pulled apart, they tend to break. The breaks often slant down, and one side slides down along the other, making an earthquake fault; Death Valley is a great example! Geoscience 10: Geology of The National Parks Unit 2 Nevada Getting Wider (with Death Valley) Lake Tahoe (California) and Snowbird (Utah) ski areas are moving apart about as rapidly as your fingernails grow (an inch or so per year)--can measure with GPS, etc. We find layers of rock offset as shown in the diagram, and earthquakes still happen and increase that offset; Lava may leak up the cracks to feed volcanoes; If this kept on, could tear the west apart to make an ocean basin; Geoscience 10: Geology of The National Parks Unit 2 DEATH-VALLEY: Tear-Apart Makes Oceans That’s what Gulf of California is; Baja California is drifting away from mainland; The breaking of the rocks has focused along a crack down the middle of the Gulf; As the rocks move away from the crack, their weight no longer squeezes the hot mantle beneath the crack; For most rocks, squeezing tends to make solid, and “unsqueezing” (a drop in pressure) favors melting; So the hot mantle under the crack melts a little, and the melt leaks up the crack and freezes. Geoscience 10: Geology of The National Parks Unit 2 DEATH-VALLEY: Tear-Apart Makes Oceans The sea floor of the Gulf of California (and of all other oceans!) is made of the frozen crack-filling lava; The sea floor is hottest, and thus highest, near the crack, forming a mid-oceanic ridge; Such ridges wind through Earth’s oceans like the seam on a baseball; Ocean-floor rocks are youngest near the ridges, oldest farthest from the ridges; Sediment (wind-blown dust, fish poop, etc.) thickens away from the ridges because older rocks have had more time for fish to poop on them; Where ridges come up on land, they are ripping continents apart, as at Death Valley and in the East African rifts. Geoscience 10: Geology of The National Parks Unit 2