Plate Tectonics

Oceanic crust - 7km thick

Old oceanic lithosphere - 120km thick

Oceanic mantle at MOR - 0km

Heat - Q_{S}=-k \frac{dT}{dz}

Thermal energy stays the same for the rising of the asthenosphere - Asthenosphere melts

Heat flux of oceanic lithosphere decreases as an inverse square root of distance

Asthenosphere is plastic, lithosphere is brittle so asthenosphere can flow

When the asthenosphere is cooled to a certain extent, it becomes brittle and becomes lithosphere

Geoid - a surface of constant gravitational potential

The geoid above the ocean is the closest to the Earth’s surface because, ignoring the moon, the water surface will take the surface of equal graviational potential

Ellipsoid - even distribution of mass, homogenous Earth, still taking into account rotation of Earth, ‘hydrostatic geoid’