Pre-Adamites?

I have recently had a discussion with a Christian who has the belief of the existence of Pre-Adamites, a race of people that were created and wiped out before Adam. I don't know what his exact beliefs on the matter are.

He is very hard to have discussions with though since he has a doctorate in Theology and is fluent in Greek and Hebrew and says that he takes all of his ideas from the original text of the Bible.

I know a lot of the idea is stemmed from the fossil layer that supposedly dates back before the time of Adam and has human remnants within it.

I was wondering if you have any material discussing this belief system or have any response to this.
Thank You for you time,
Michael