How do we know when the Gospels were written?

Question of the week:  We had one of our readers ask this week if there were any books written during the life of Jesus. And correspondingly, how do we know when the books of the New Testament were written.

We will try to condense the rationale on the dating. It’s really difficult to pinpoint dates unless the writer talks about specific people (e.g. Pontius. Pilate) or an event (e.g. the destruction of the Jewish Temple in the 70s CE). But here goes. 
First, Jesus died around 30 CE. The stories around his life and death were likely all oral traditions in Aramaic.

Paul’s letters were written in the 50s CE. He makes no mention of any written works about Jesus. So that seems to indicate the first works had to be written after Paul’s death around 60 CE. With that prelude:

• Mark.  Most scholars believe Mark was the first book written. And they date it prior to 70 CE because the author does not talk about the destruction of the Temple (in the 70s CE). So it seems likely this book was written after Paul’s letters and before the Temple was destroyed.

• Matthew and Luke both refer to the destruction of Jerusalem. So they must have been written after 70 CE. They also appear to have lifted (copied/plagiarized?) some of the stories written in Mark.

• John is probably the most difficult to pinpoint. It contains different stories from the other three Gospels. And it contains a theological development that is more evolved than the other three (and is also more evolved than the 3BT Chief Editor’s ability to summarize). Some scholars argue that it could have been written sometime in the early second century. But most have settled on around 90 CE.

And to put a book-end on the latest probable date, A guy named Justin Martyr made the first allusion to Memoirs from the Apostles in 150 CE. But even then he does not call them Matthew, Mark, Luke and John. Unfortunately, we do not have any actual scrolls or books dated in the first century. But scholars think that Justin Marty’s reference must mean that by 150 CE, the four gospels were likely compiled.