 When we look at cooling and transferring of heat out of the interior of the earth we see convection of the mantle, the overturning of the mantle as being the simple pot boiling that if you make porridge you can tell that if you just look at the pot and the heat that goes into it makes it less dense so it rises and then when it cools it becomes more dense so it sinks. The idea is that the outflow of heat comes in the plumes and then we take stuff back down and so we have this rotational thing and you can imagine that as it gets down deep again but the biggest player of taking the convection back are the slabs that are returned so that once we made some oceanic crust and once we started subducting them that's the return of material back into the earth. It's very cool in fact as it enters the earth it's pretty much room temperature so that we're taking room temperature stuff and putting it down there where it's 2,000 degrees so obviously it gets turned into all the minerals so as the slab goes down it's returning back down and as it comes down it's metamorphosing to different crystalline stuff so that what we start with at the top which is basalt and sediments is nothing like what we have as we get down there right so that's amazing because we're simply transforming it into different phases. Interestingly as the slab goes down when it gets to a certain depth it will be it will contain hydrous minerals like chloride at a certain depth that chlorides no longer stable and it loses its water. That water goes into the mantle above the slab and causes the mantle to melt. That melt then produces a magma which can rise up fractionate, crystallize and form granitic rocks and volcanoes so at that point where we absolve the water always produces magma and that magma is so buoyant that it goes straight up so that that point is what we call a volcanic arc and every subduction zone has a magnetic arc so Japan would be a good example of a magnetic arc as well as the Andes as well as Indonesia a whole bunch of volcanoes and that is taking taking heat out of the earth and it's doing it continuously. The other place we're doing it is at the mid-ocean reaches. This is a great place to get heat out and that's a big part of the convection. Okay we've got the plumes we've got the subduction zones where we got magnets coming out but more importantly the most shallow place where the mantle comes up and it melts because it's decompressing is the mid-ocean reaches. So it's like a stitch all the way up the middle of the Atlantic Ocean all the way up the middle of Pacific Ocean. There's one between us and Antarctica which left about a hundred million years ago used to be attached to us but as it comes up it spreads and we make basalt and the basalt very slowly adds out. That's a reflection of the fact that we are convecting the mantle.