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INSIDE THE EARTH. The Crust, Mantle, Core and Plate Tectonics. Cutaway view (not to scale). The Crust. The outermost layer, is rigid and very thin. Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km.
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INSIDE THE EARTH The Crust, Mantle, Core and Plate Tectonics
The Crust • The outermost layer, is rigid and very thin. • Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km. • The thickness of the crust beneath continents is much more variable, about 30 km, under large mountain ranges, such as the Alps. • The base of the crust can be as deep as 100 km. • Like the shell of an egg, the Earth's crust is brittle and can break.
The Mantle • Dense, hot layer of semi-solid rock approximately 2,900 km thick. • Contains more iron, magnesium, and calcium than the crust. • Hotter and denser because temperature and pressure inside the Earth increase with depth.
The Core • Nearly twice as dense as the mantle because its composition is metallic (iron-nickel alloy). • 2,200 km-thick liquid outer core. • As the Earth rotates, the liquid outer core spins, creating the Earth's magnetic field. • 1,250 km-thick solid inner core.
Plate Tectonics • Earth's internal structure influences plate tectonics. • The crust and upper mantle form a rigid layer of rock called the lithosphere. • Thinnest under the oceans. (80 Km.) • Below the lithosphere is a relatively narrow, mobile zone in the mantle called the asthenosphere. • Lithosphere is thought to "float" or move about on the slowly flowing asthenosphere.
What Drives the Plates? • The plate-driving force is the slow movement of hot, softened mantle that lies below the rigid plates. • The mobile rock beneath the rigid plates is believed to be moving in a vertical circular manner. • This cycle is repeated over and over to generate a convection cell.
Divergent Boundaries • Occur along spreading centers where plates are moving apart. • New crust is created by magma pushing up from the mantle.
Convergent Boundaries • Crust must be destroyed at about the same rate as it is being created. • Destruction (recycling) of crust takes place along convergent boundaries. • One plate sinks (is subducted) under another in a Subduction Zone.
Transform Boundaries • The zone between two plates sliding horizontally past one another. • Most transform faults are found on the ocean floor. • A few occur on land, for example the San Andreas fault zone in California.
Plate Tectonics and People • Earthquakes. • Volcanoes. • Tsunamis. • Geothermal energy. • Fertile soil.
Earthquakes • Occur in specific areas, such as along plate boundaries. • One such area is the circum-Pacific Ring of Fire, where the Pacific Plate meets many surrounding plates. • Mid-plate earthquakes are those occurring in the interiors of plates.
Volcanoes • Volcanic eruptions are one of Earth's most dramatic and violent agents of change. • Powerful explosive eruptions drastically alter land and water. • Tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet's climate temporarily.
Strombolian-type Eruption • Huge clots of molten lava burst from the summit crater to form luminous arcs through the sky.
Vulcanian-type Eruption • A dense cloud of ash-laden gas explodes from the crater and rises high above the peak.
Vesuvian type Eruption • Great quantities of ash-laden gas are violently discharged to form cauliflower-shaped cloud high above the volcano.
Hawaiian type Eruption • Molten, incandescent lava spurts from a fissure on the volcano's rift zone and feeds lava streams that flow downslope. In central-vent eruptions, a fountain of fiery lava spurts to a height of several hundred feet or more.
Plinian type Eruptions • The most powerful eruptions are called "plinian" and involve the explosive ejection of relatively viscous lava. Large plinian eruptions can send ash and volcanic gas tens of miles into the air. Fast-moving deadly pyroclastic flows are also commonly associated with plinian eruptions.
Tsunamis • Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. • When large areas of the sea floor elevate or subside, a tsunami can be created. • Subduction earthquakes are particularly effective in generating tsunamis.
Geothermal Energy • Our earth's interior - like the sun - provides heat energy from nature. This heat - geothermal energy - yields warmth and power that we can use without polluting the environment. • Geothermal water travels up through faults and cracks and reaches the earth's surface as hot springs or geysers.
