Christians often point to chapter 15 in 1 Corinthians as important evidence for the resurrection. This book, Paul’s first epistle to the church in Corinth, was written roughly a decade before the earliest gospel of Mark (written in c. 70 CE). This makes it the earliest claim for the resurrection of Jesus.
Let’s see if the story holds up. Here’s the section that many Christians point to:

For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to [Peter], and then to the Twelve. After that, he appeared to more than five hundred of the brothers and sisters at the same time, most of whom are still living, though some have [died]. Then he appeared to James, then to all the apostles, and last of all he appeared to me also, as to one abnormally born. (1 Cor. 15:3–8)

Claims about the dating of this important passage are all over the map. Some argue that it actually precedes Paul’s writing. They say that it appears to be in a different style, as if it were a creedal statement (like the modern Apostle’s Creed) that would have been recited by believers. That is, though Paul wrote this epistle 25 years after the crucifixion, it had been an oral creed since as early as a few years after Jesus’ death. They cite this as evidence that belief in the resurrection was years earlier than Paul’s writing.
But if it’s a creed, it’s not evidence. A creed is a faith statement—a statement of what people believe. It even sounds like one. There is no mention of time or location, like a police report or newspaper article would have, and “Christ died for our sins” isn’t an observation, it’s a faith statement.
Others propose a very different interpretation: that the different style suggests that it was added to copies decades after Paul’s writing. The gap from the creation of this epistle to our oldest copy is about 150 years. That’s a lot of opportunity for hanky-panky as scribes copied and recopied the letter, especially during the early turbulent years of the new religion of Christianity. We can’t know for certain what the original said.
Now consider more questions about this chapter.

• Jesus was “raised on the third day according to the Scriptures.” This is a reference to Jonah 1:17 (“Jonah was in the belly of the fish three days and three nights”), but how can the resurrection of Jesus be “according to” this scripture? That verse in Jonah is hardly a prophecy.
• Jesus appeared “to the Twelve”? But they were Eleven after Judas was gone, and his replacement was elected after the ascension of Jesus.
• “Christ died for our sins”? Here, the sacrifice of Jesus parallels the Old Testament animal sacrifices. But later in this chapter, Paul discards this by saying, “if Christ has not been raised, your faith is futile; you are still in your sins” (15:17). So he’s apparently changed his mind, and now it’s the resurrection that is the saving act.
• Paul says, “and last of all he appeared to me also.” But the appearance to Paul as recorded in Acts 9:3–9 was a visionary sighting (his companions at the time saw nothing). Is Paul’s list of appearances above a combination of visionary and actual sightings? If so, which of the others are visionary as well?
• Later in the epistle, Paul says, “For as in Adam all die, so in Christ all will be made alive” (15:22). This is nice symmetry—we didn’t do anything to get tarred with the brush of Adam’s sin, and we don’t need to do anything to get the redemption of Christ—but most Christians don’t think everyone’s going to the same place.
• Paul says, “the Son himself will be made subject to him who put everything under him, so that God may be all in all” (15:28). This isn’t too surprising, since our concept of a Trinity of co-equal persons was developed in the fourth century, but it does highlight the fact that Paul might be shocked by what Christianity has become.
• Paul says, “The body that is sown is perishable, it is raised imperishable … it is sown a natural body, it is raised a spiritual body” (15:42–4). This makes clear that the resurrected Jesus was spirit, not flesh. This sounds a lot like docetism, a heresy that was rejected in the First Council of Nicaea. It also contradicts Luke’s physical post-resurrection Jesus: “Touch me and see; a ghost does not have flesh and bones, as you see I have” (Luke 24:39).
• We’re told that Jesus “appeared to more than five hundred of the brothers and sisters at the same time.” But later, after Jesus rose into heaven, the believers were “a group numbering about a hundred and twenty” (Acts. 1:15). The 500 can’t have been too impressed with what they saw if they weren’t all believers. And if Paul’s claim is such compelling evidence, why didn’t any of the gospels include it?

Though an important bit of history, this chapter may not be as compelling as believers think.

The book [of Mormon] is a curiosity to me.
It is such a pretentious affair and yet so slow, so sleepy,
such an insipid mess of inspiration.
It is chloroform in print.
— Mark Twain

Acknowledgements: I’ve gotten some of these points from The Atheist’s Bible Companion to the New Testament by Mike Davis, Nailed by David Fitzgerald, and one particular sharp-eyed commenter.
Photo credit: Codex Sinaiticus project