Plate Tectonics Lithosphere- 60 miles thick (crust and upper part of the mantle.) It is the solid outer layer of earth made up of tectonic plates. Plate tectonics is the theory that large pieces of the lithosphere move and change shape.

Plate Tectonics Asthenosphere- hot, plastic portion of the mantle Hypothesis 1- the plates of the lithosphere float on top of the asthenosphere Hypothesis 2- the plates are driven by the force of gravity acting on their own massive weight.

Plate Boundaries Volcanoes and earthquakes are more likely to occur where tectonic plates meet. Mountains and rift valleys also occur along plate boundaries.

Mid Oceanic Ridges Mid oceanic ridges are mountain ranges in ocean crust. In the center of the ridge is a rift valley. Divergent Boundary- two plates move apart and a gap is made. Hot rock then rises and oceanic crust is made.

Subduction Convergent Boundary- where older lithosphere is destroyed. Subduction- When one tectonic plate moves beneath another. The Andes Mountains were made this way.

Miscellaneous Subduction of ocean crust makes volcanoes. Islands could form where two plates meet Colliding tectonic plates create mountains