If someone has a u.s green card is that as good to use as identiication to travel out of the country or do they have to obtain a passport from their place of birth.

Green card is entirely different. It shows that you are here under a legal status. It does not mean it can be used like a passport. Having said that what it would allow is for you to travel to your home country and back again. But other then that its not good for any other country. You would need a passport from your country of origin.