First, there is the telling fact that two of the oldest and most highly respected Bible manuscripts, the Vaticanus 03 and the Sinaiticus 01, do not contain this section; they conclude Mark’s Gospel with verse eight. This is true of the early versions as well: Syriac, Coptic, Armenian, and Georgian. The early church fathers, Clement, Origen, Cyprian, and Cyril of Jerusalem had no knowledge of anything beyond verse eight.
Codex Sinaiticus (01, א) alone has a complete text of the New Testament and portions of the Greek translation of the Hebrew Scriptures known as the Septuagint. It is a vellum manuscript written in Greek dating to c. 330–360 C.E. The Codex Sinaiticus Project has described the Sinaiticus as “one of the most important books in the world.”