How Do We Determine When the Gospels Were Written?

The dating of the Gospels is very uncertain. One New Testament scholar aptly compared it to a line of drunks reeling arm-in-arm down the road – if one falls, the other falls; they're so interdependent. It seems very likely that Matthew and Luke used Mark. It may even be the case that Luke used Matthew in writing his own Gospel. John seems to be independent of the other two. But it's very difficult to determine exactly when these were written. I myself am persuaded that the Gospel of Luke and the book of Acts was written prior to the fall of Jerusalem in AD 70. The reasons for that are multifarious. In the book of Acts, Paul is still alive under house arrest in Rome when the book of Acts ends. It has a sort of dropped ending. It doesn't tell the result of his trial. That suggests that when Luke-Acts was published that Paul was still in Rome awaiting his trial, which would mean (given that Paul was executed in the mid-AD 60s) that Luke-Acts was written prior to that. Moreover, there is no mention in the book of Acts of very significant events that took place in the AD 60s. The most prominent of these would be the destruction of Jerusalem in AD 70 which isn't mentioned in Acts, even though that would have been catastrophic for the early Christian church which was based in Jerusalem. Moreover, there's no mention of the martyrdom of Jesus’ younger brother, James, who was the leader of the New Testament church in Jerusalem which we know from Josephus occurred, again, during the AD 60s. And there's a number of other such events that were not mentioned in the book of Acts which makes it very hard to believe that Acts was written after these events. Now, if that's true, and Luke was written prior to Acts (which is the sequel to the Gospel of Luke), that means Luke was written prior to the AD 60s, probably sometime in the late AD 50s. And if Luke used Matthew and Mark, that could put Matthew and Mark in the early 50s, maybe even put Mark in the late AD 40s. That's just 10 years after the crucifixion of Jesus. So the window between the time of the events and the publication of the record of these events is very, very narrow indeed which I think redowns to the historical credibility of these documents. Now, of course none of this is open and shut. The arguments are disputed. But I, at least, do find these arguments for the early dating of Luke-Acts to be very persuasive.