Lithosphere Thickness
The crust of continents and ocean are made of different kinds of rock.
They vary in thickness and conduct heat flow differently.
![](http://www.ei.lehigh.edu/learners/tectonics/heatflow/basalt.jpg)
Oceans are basaltic. Ocean crust is only 0-10 km thick. This is much thinner than continental crust. The thinner crust, along with relatively rapid hydrothermal circulation, allows more of the Earth's interior heat to conduct through.
![](http://www.ei.lehigh.edu/learners/tectonics/heatflow/granite.jpg)
Continents are granitic. Continental crust is 35-70 km thick. This is much thicker than oceanic crust. The thick crust acts like an insulating blanket, reducing heat flow from the interior to the surface.