From a link that Flow provided in another thread...
Gospel of Mark changed 100 years after it was written??As an example, the Rt. Rev. Alexei Smith, ecumenical and interreligous official of the Roman Catholic Archdiocese of Los Angeles, quoted from the Gospel of Mark: "Go into the world and preach the gospel to the whole creation. He who believes and is baptized will be saved; but he who does not believe will be condemned."....
...In explaining the passage from the Gospel of Mark, Smith said that the troubling portion was appended a century after it was written -- when the four Gospels were compiled.
He said the longer ending, which added 12 verses, was written at a time when Christians either were questioning their faith in the resurrection of Jesus or defending it against skeptics and nonbelievers.