Challenge that stand in way of sending explorers to the center of the earth?

Challenges that stand in the way of sending explorers to the center of the earth are, the heat is way too intense, it would burn them up in a second, there is so much pressure that with the burning it would smash them.  

Explanation:

they use tree rings to figure out weather patters.

the correct answer would be true friction causes the faults to slip or collide