An atheist says there are no original manuscripts of the woman caught in adultery, yet it's in our Bibles. How do you answer?

We have no original autograph of any book of the New or Old Testament; those original documents are gone, or we have no idea where they are. What we have are copies, some five thousand Greek manuscripts, from fragments to full codices. Two famous papyri, P66 and P75, differ over the woman caught in adultery, and the codices Sinaiticus and Vaticanus differ too, which is the ordinary work of textual criticism, one of the valid parts of historical criticism. A few other passages, like Mark 16:9-20 and 1 John 5:7, have the same kind of mix. But when you add it all up, there is less than one percent discrepancy among all the Greek manuscripts, which is remarkable, so we can be confident we have the original New Testament.