it's a hw question i cant find a good answer to in my book
2007-09-20 10:59:28 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Earth Sciences & Geology
The outermost part of the Earth's interior is made up of two layers: above is the lithosphere, comprising the crust and the rigid uppermost part of the mantle. Below the lithosphere lies the asthenosphere. Although solid, the asthenosphere has relatively low viscosity and shear strength and can flow like a liquid on geological time scales. The deeper mantle below the asthenosphere is more rigid again. This is, however, not due to cooler temperatures but due to high pressure.
The lithosphere is broken up into what are called tectonic plates—in the case of Earth, there are seven major and many minor plates. The lithospheric plates ride on the asthenosphere. These plates move in relation to one another at one of three types of plate boundaries: convergent or collision boundaries, divergent or spreading boundaries, and transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries. The lateral movement of the plates is typically at speeds of 0.66 to 8.50 centimeters per year (the speed at which human nails grow).
2007-09-21 09:05:41 · answer #1 · answered by Monty 3 · 0⤊ 0⤋
The quick and dirty (aka intro geology) explanation is that plate motion is a result of mantle convection. Hot mantle rises, cooler mantle sinks. This circulation causes the plates to move along the aesthenosphere.
2007-09-20 11:05:11 · answer #2 · answered by Lady Geologist 7 · 0⤊ 1⤋