It is a really really simple experiment :D We dug foundation, like 1,80-2 meters deep. And the dirt near the surface was room temperature, the dirt on the bottom was warmer, even it was whole day in shadow, and it was warmer at night and at dawn too. So several hours later then it was moved/dig, so no friction generated the heat, and there wasn't any piping under or near it.
Another experiment, even simpler.
I was in several caves and closed mines open to tourists, hundreds of meters deep, and it was like a sauna. Most of them had not artifical ventillation or lightning so it coudn't create the heat, and there was only like a dozen people in a huge ass chamber, so people or other animals also couldn't produce that much heat. :)
Why no lava? Lava comes from the molten core, 3000+km deep. The deepest drill was 12km. The Crust is ~30km thick. We didn't even reach the mantle :o :D
Oh! And if lava, how do you explain volcanoes? They don't exists right? :o :D
http://www.bbc.co.uk/staticarchive/18e0518ed5183cd531f908f11031e176c4461b9c.gifnice cartoon pic......happen to have a real photo of the inner core and outer core?
No? so you just accept hearsay (someone else's word) that there is a molten core as solid evidence?
I don't know why it is warmer below the surface, and neither does science. They just guess and make up theories.