I didn't know that it was a Carter Family song but it went like this:

"Oh my lovin' Brother, When the world's on fire, You need my Jesus, To be your savior."

And as far as the folk process is concerned, I've heard Pete Seeger quote Woody as saying about someone who stole a tune of his, "He just stole from me, Hell, I steal from everybody."

You can hear traditional melodies in songs from the Beatles to the "We are the World" bunch. So as Willie Nelson sang, "Let's settle down and steal each other's songs."