[thackney]

No matter how deep in the earth we drill (up to 7 miles), we encounter hydrocarbon gases.

In sedimentary basins. Places where sediment from the surface has accumulated.

We don't find that in igneous rock, where the mantle has pushed up from the deep.

[lacrew]

I think there are still some mysteries out there. Didn’t the Soviets drill very deep and find hydrogen?

I’m probably thinking about this:

http://en.wikipedia.org/wiki/Kola_Superdeep_Borehole

Deep in granite...and they found hydrogen.