The John Rylands papyrus (pS2) is the oldest copy yet discovered of any portion of the New Testament, dating back to the first half of the second century A.D. A tiny fragment of a codex (a leaf-form text, like a modern book, in contrast to a scroll) of the Gospel of John, it contains parts of John 18:31-33 on one side and verses 37-38 on the other. It was acquired in Egypt in 1920 and now resides in the John Rylands Library in Manchester, England.
Despite its tiny size (less than 3.5 in. [9 cm] from top to bottom), this papyrus fragment is highly significant. It testifies that by the first half of the second century the Gospel of John was already being read in Egypt, far from Ephesus in Asia Minor, the most likely place of its composition. It seems unlikely that John’s Gospel could have been composed much later than the end of the first century, since it would have taken time for it to have been accepted and disseminated so far from its place of origin. The manuscript of which pS2 is a fragment may have been copied within 25 to 30 years of the composition of the Gospel itself. If we take into account that in some pieces of Greek or Latin literature the oldest manuscript available is dated to over a thousand years after the composition of the original text, that is in reality an extremely short period of time. An enormous number of Greek New Testament texts exist, and they give us good reason to be confident that the New Testament we read today accurately reflects what was in the original manuscripts.
Source: New International Version Archaeological Study Bible