Some great advice already given and a great starting point from Patricia. But this happens a lot as you are going back in time, just for next time...
I would do it the hard way first, as your watchlist grows you may forget to go back and do the research, you can add it to your to do list to remind you, but you may as well get it done and dusted now (learned from experience!!)
I find the earliest way is to log into familysearch not using the rootsearch tool but off wikitree. Assume that as the father is listed in the marriage cert that his parents were married. If he's on the birth cert/baptismal record then even better. The youngest the parents could (in most cases) have been when the child was born is 18, the oldest..... Up to you, I would start with late 30's. See how many sources are found and start to experiment with educated guesses, like Ros says, educated guesswork sometimes can take you where you need in seconds, or hours, or sometimes days and weeks with more common names!
Good luck with it :-)