Debunking the Legend

It seems that athiests are fond of saying that the gospels are not reliable because they were written in the early 2nd century by people who were not eye witnesses (not the guys the books were named after). So, generally it's believed that the story of the resurrection surfaced as legend at some point after years of oral communication and eventually made it into the gospels well after the actual events. The problem is that the resurrection of Christ is referenced throughout Paul's letters which are widely accepted to have been written in the 50s (first century, obviously). So if the gospels were written later and these late breaking documents introduced the concept of the resurrection, how did Paul find out about it 20 years after Jesus' death? Clearly the "legend" of the resurrection was widely in circulation at the time of Paul's writings and was not introduced in the second century at all. Also, it was in circulation while eye witnesses were still alive to dispute it.