Earth"s crust: continental crust (low density) 35 km thick 2. 6 grams more dense than water (1, oceanic crust (high density) 10 km thick 3. 2 grams more dense than water (1) Tectonic plate is not just the earth"s crust but also includes interior. Plate tectonic model: lithosephere = thin, cool, and hard, asthenosphere = weak and hot, lithosphere broken into large fragments called plates, plates float on asthenosphere, plates move around and interact w/ each other. Isostasy: plates float @ an elevation depending on thickness and density, required pressure to be equal, himalayas are high due to deep root. Plate boundaries can be: divergent : moving away from each other, convergent: moving towards each other, transform: moving past each other. Plate tectonics: on the move: pangea (greek : all lands, starting 200 million years ago, continents started to drift away from each other led to continental drift hypothesis wasn"t accepted.