Why is the magma in the below the earths crust still hot and flowing?
The basic answer is, the earth does not have a good way to cool itself. In general, there are two major ways for a substance to cool. One is conduction, which involves transferring heat energy to another medium. This is the usual mechanism we are familiar with for cooling – putting ice in a drink to cool it, for example, results in heat flowing from the drink into the ice cubes. Conduction is extremely efficient. The other way is radiative cooling – emitting energy directly in the form of light. This is how a light bulb works – it is so hot that it gives off energy in the form of visible light. This sort of cooling is governed by what is called “blackbody radiation” – the energy of the light you emit is dependent on your temperature. Light bulbs are extremely hot, so they radiate mostly in the visible spectrum. By comparison the earth, on average, is not as hot – it radiates only in the infrared. There is nowhere for this energy to escape via conduction – the Earth is surrounded by vac
