What does this mean..?

What does it mean when people say we're born of the earth, and so shall go back into the earth after death? Or something like that. Don't remember the exact phrases. I understand the part about death, coz we're buried into the soil. But the one about birth? How are we born out of the soil? Aren't we created biologically? Can someone explain to me what that philosophy means, and where it came from?