Peter, it is believed, was finally executed in 67, and the gospel finally written in the year 70. In the meantime his preaching had been recorded.
Mark was at one time or another a travelling associate of Paul (2 Timothy 4:11), Barnabas (Acts 15:39) and Peter (1 Peter 5:13). He was in good company and had plenty of reliable sources to get his accounts from. However Mark did not sign his Gospel so there is no real way of knowing who wrote it. The earliest reference we have to the authorship of Mark's Gospel comes the Church historian Eusebius, Bishop of Caesarea (c. 320 AD). He quotes Papias, Bishop of Hierapolis (c. 130 AD), who recorded a tradition which he claimed was handed down by an elder, that Mark was a companion of Peter. Papias also records that Mark wrote down accurately Peter's account of the sayings and doings of Jesus, though not in order.
The flow of Mark's story is relatively straightforward. It starts from when Peter turned up on the scene at the river Jordan (Mark 1: 16 - 17). There is no account of the birth story, genealogy or the shepherds. Mark starts from the public ministry of Jesus, when he (Jesus) was about thirty years. It goes straight into the action with the very first chapter containing miracles. In all The Gospel of Mark records 18 miracles of Jesus (a similar number to Matthew and Luke) but only 5 parables compared to the 18 in Matthew and 19 in Luke.
The Gospel of Mark shows the humanity of Jesus. It gives us an insight into the emotions of Jesus such as him appearing sorrowful (14:34), disappointed ((8:12), displeased (10:14), angry (11: 15-17), amazed (6:6) and fatigued (4:38).
At an undisclosed date Jesus makes the journey to the River Jordan to be baptized by John. It turns out to be a pivotal moment in his life. The heavens are torn apart (Schizo), the Spirit descends on him like a dove and a voice proclaims, "You are my Son, whom I love; with you I am well pleased" (1:9-11).