We walk all over it every day of our lives. We plow it, we dig it, and we drill it; we cover it up with concrete. We map it and we measure it; we draw our borders onto it; and we imagine that it belongs to us. We live by what it produces, and we bury our dead in it. We take its existence for granted; it seems invincible, indestructible. If we consider our planet to be an organism, its crust - just 40 kilometers thick - is its most delicate organ by far.