Re: Is it a possibility for the earth to run out of magma?

Dear Spencer,

In order to answer your questions, I have to begin way back at the earth's 
formation so please bear with me! The earth formed around 4.5 billion years 
ago by the accumulation of rocky bodies like meteorites and asteroids.  At 
that time the earth was very hot - mostly molten - and did not yet have a 
core, mantle and crust.  Over time, the core formed as heavier metals sank 
out of the molten material which we call magma.  The crust formed at the 
surface of the magma, sort of like the skin that forms on your hot 
chocolate. The mantle is made of the remaining magma.

Since that time, the Earth has been slowly cooling down. This is important 
to your question about the mantle burning through the crust. Because the 
entire Earth is much cooler now, the mantle is not hot enough to burn or 
melt the entire crust. It also helps that the crust has thickened over time 
too. On the other hand, the mantle does still have enough heat to burn 
through certain parts of the crust - thats what volcanoes are!  

As for Earth running out of magma, yes, this will happen.  This is because 
the Earth will eventually cool off completely, causing the mantle to 
solidify. Since the mantle is the source for magma, that means no more 
magma, too.  This has already happened to Mercury!          

Thanks for your question!

Diane Hanley


Reference:  

Thomas R. Watters, 1995. Planets, A Smithsonian Guide. MacMillan Publishing 
Compan