You are Just Digging Yourself Deeper.....

These two were heard pretty close together in a Chem-Comm (Pre-Chemistry) Class. The discussion was on extracting ores, and digging for minerals et cetera. The question posed was: How far is it to where there is lava in the middle of the Earth?

Teacher: Well, look. {Draws crossection of the layers of the earth on board} This is the crust. That is what we are standing on, and.....
Student: Whoa! Wait a minute!!! We are standing on the CRUST!?!?!?!? I thought we were standing on the atmosphere....

- - After explaining that, Teacher is recapping how far it is to the 'lava' (it would actually be magma, but you know, we don't want to expect too much), and gives his final figure to the magma. - -

Same Student: {turns to buddy} You know, that couldn't be that far.....I can dig that in a year and a half, with a pickaxe!!! Maybe a year, if you helped....