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Earth’s Interior Earth’s Interior • Earth’s interior is made up of 5 zones: 1. Crust: ~25 km in depth. It is like the skin of an apple. The crust varies in thickness; thinner oceanic and thicker continental. 2. Mantle: 2900 km in depth. It is the largest of Earth’s zones. It is solid rock, but parts of it flow slowly upward or downward, depending on whether it is hotter or colder than the mantle next to it. • Lithosphere: ~100 km in depth. It includes the crust and the uppermost part of the mantle. It is relatively rigid. • Asthenosphere: ~100 km in depth. The uppermost mantle underneath the lithosphere. It is soft and flows more readily than the mantle. It provides a layer over which the lithosphere moves. • Core: 3470 km in depth. It is the center of the Earth. There is a solid inner core and a liquid outer core. Plate Tectonics Theory of Plate Tectonics • Tectonic forces: forces generated inside the Earth cause de-formation of rock as well as vertical (↕) and horizontal (↔) movement of portions of the Earth’s crust; most are mechanical forces. • Plate tectonics is a unifying theory that accounts for seemingly unrelated geologic events. –Explains where and why we get earthquakes, volcanoes, mountain belts, deep ocean trenches, and mid-oceanic ridges. • Plate tectonics was seriously proposed as a hypothesis in the early 1960s, though it was based on the theory of continental drift. –Continental drift stated that the continents drifted over the crust. Boundaries • Plate tectonics regards the lithosphere as broken into plates that are in motion; moving relative to one another, sliding on the underlying asthenosphere. • There are three types of plate movement: – Divergent boundaries – Convergent boundaries – Transform boundaries Divergent Boundary • These boundaries exist where plates move apart. • Most are under the ocean and create giant mountain ranges, called mid-oceanic ridges. • New oceanic crust is continuously being created (sea-floor spreading). • The rate of motion is usually 1-18 cm/y. Convergent Boundary • The plates are moving toward each other. • Oceanic crust is forced underneath the continental crust; this region is called a subduction zone. • Old oceanic crust is destroyed, producing magma and causing earthquakes. • On land, mountains are created from convergent boundaries. • Under water, trenches are created. • There are 3 types: – Continental plate with continental plate – Continental plate with oceanic plate – Oceanic plate with oceanic plate Transform Boundary • Occurs when two plates slide past each other; often causing earthquakes. • It is also known as a Transform Fault Boundary because it creates faults. • No new crust is created, or old crust destroyed.