Is the Bible really written by one guy?

I ran into this argument all the time from atheist all of the time. The Bible has nothing to do with history. It was made up by some guy who lived 100 years after Jesus died. Now is this true? No for one what would be the motivation behind that. Not only has the Old Testament has been written over a thousands years by different. Even using measurements of money that was not used in the time period they claim it was written but Judaism. The last book of the Old testament The book of Malachi was written in 440 B.C. That would be about 473 years before Jesus' birth.

Now another argument I heard the New Testament was made up written by one guy. If this was the case why does not the four Gospels match up 100%. See the reason behind that is that their where four different views from four different people and where they where at the time. So the case of this being written by the same guy falls apart because if that where true they would match up backing the others claims but since they where four different people that have different experiences remembering things a little different or seeing things the other guys did not witness. In fact Luke was not even one of Jesus' 12  disciples. He was a doctor that can around after the fact to get eyewitness accounts not only from his followers but the people who where their as he states in Luke 1:1-4 Many have undertaken to draw up an account of the things that have been fulfilled among us, just as they were handed down to us by those who from the first were eyewitnesses and servants of the word. 3 With this in mind, since I myself have carefully investigated everything from the beginning, I too decided to write an orderly account for you, most excellent Theophilus,  so that you may know the certainty of the things you have been taught.

If you agree disagree or have any thoughts just post below.