From what I gather, all credible sources cite Paul’s Epistles as the oldest NT writings. Of the Gospels however, Synoptic Gospels plus the 4th Gospel, they begin with the book of Mark, the earliest of all the Gospels. General consensus among scholars is that it was written circa 60-70 A.D. (C.E.). Both Bart D. Ehrman's seminary text book entitled The New Testament and Biblical scholar Raymond E. Brown’s International version of An Introduction to the New Testament are great resources for answering questions on dating the Synoptic Gospels, Paul's Epistles, and more. I’ll also be intermingling and weaving in some Wikipedia sources which are very heavily referenced in detail, and should help you get started investigating the crux of the matter in full.
Browsing through the Synoptic Gospels, the first three gospels of the New Testament, we discover that the canonical order of these Gospels follows the tradition that the book of Matthew came first. This was originally proposed by the fifth century bishop Augustine of Hippo. He did so to try and explain the consistent relationships between the Synoptic Gospels by proposing that Matthew was written prior to Mark which in turn used Matthew as a source. Finally Luke was presumed to have been written using Matthew and Mark as its sources. John, often called the Fourth Gospel, seems to stand apart from the others for various textual reasons which we'll discuss later on.
The precise nature of the relationships between the gospels of Mark, Matthew, and Luke is known as the Synoptic Problem. The recognition of the question, and attempts to resolve it, date to antiquity. For example, Augustine of Hippo tried to explain the relationships between the synoptic gospels by proposing, as mentioned earlier, that perhaps Matthew was written first. This would explain the similarities then in Mark using Matthew as a source. Finally, following Augustine of Hippo's suggestion that Luke was written using Matthew and Mark as sources we get a theoretical chronology for the order of the Gospel texts. Although, it's worth noting that this specific solution has fallen out of favor among modern scholars. When Augustine wrote the Dead Sea Scrolls and Nag Hammadi library were not yet recovered and the evidence for the Lost Gospel of Q (e.g. the Q document) was not yet readily available.
The above mentioned archeological discoveries have forced modern scholars to reject Augustine of Hippo's theory knowing that the Gospel of Mark, not Matthew, was the earliest written canonical Gospel. However, the exclusive relationship between the three texts, especially the near duplication of wording and structure in some parts of Matthew and Luke, still needed to be explained.
There are differing opinions as to how late Mark could have been written. Most scholars agree with the Two-source hypothesis that proposes that Mark was one of the sources for the other Synoptic Gospels, Matthew and Luke; according to this viewpoint the latest possible date for Mark depends on the dating of Matthew and Luke. A wide range of recent critical scholars believe that Mark was written at the earliest after the fall of Jerusalem and the destruction of the Second Temple in 70.
Two papyrologists, Fr. Josep O'Callaghan and Carsten Peter Thiede, have proposed that lettering on a postage-stamp-sized papyrus fragment found in a cave at Qumran, 7Q5, represents a fragment of Mark (Mark 6:52–53); thus they assert that the present gospel was written and distributed prior to 68. Computer analysis has shown that, assuming their disputed reading of the letters to be correct, and allowing for the replacement of one letter and the omission of a three word phrase "to the land", only Mark matches these twenty letters and five lines among all known Greek manuscripts. The majority of papyrologists question this identification of the fragmentary text, for several reasons. Some assume that all early papyrus Gospel manuscripts were copied as codices., and that a copy in a scroll format would not have been made for the Qumran librarians. While no other known Greek work matches 7Q5's wording, neither does Mark unless the phrase "to land", found in all other extant manuscripts of Mark, is omitted from 6:52–53.
John A. T. Robinson in 'Redating the New Testament' proposes an even earlier date. He accepts Marcan Priority and dates Luke/Acts no later than 62. Therefore, if Mark was written before Luke/Acts, Robinson dates Mark to the mid-fifties. Whereas the dating of Mark near AD 70 is based on apparent references to the destruction of the Temple in Jerusalem, combined with the assumption that the first readers would not have understood these references if the gospel had been written prior to the events described.
The relationships between the three synoptic gospels go beyond mere similarity in viewpoint. The gospels often recount the same stories, usually in the same order, sometimes using the same words. Subsequently, following Mark are the Gospel books of Matthew and Luke.
The date of Matthew is still a matter of debate among Biblical scholars. Many believe it was composed between the years 70 and 100. The writings of Ignatius show "a strong case ... for [his] knowledge of four Pauline epistles and the Gospel of Matthew", which gives a terminus ad quem of c. 110. The author of the Didache (c 100) probably knew it as well. Some scholars see the prophecies of the destruction of Jerusalem (e.g. in Matthew 22:7) as suggesting a date of authorship after the siege and destruction of Jerusalem in 70 AD: However, John A. T. Robinson argues that the lack of a passage indicating the fulfilment of the prophecy suggest a date before that. Matthew does not mention the death of James in 62 AD. It also lacks any narrative on the persecutions of the early Christians by Nero.
Scholars note that the similarities between Mark, Matthew, and Luke are too great to be accounted for by mere coincidence. Because multiple eyewitnesses reporting the same events never relate a story using identical words, scholars and theologians have long assumed that there was some relationship between the three synoptic gospels that was based upon common literary sources.
Extensive copying between all three texts, which were written separately around 70 CE, turns out to be the result of another document referred to by scholars as Q. Stemming from the German word Quelle, which means “source” in German, historians have postulated that there is a lost textual source for the Gospel of Matthew and Gospel of Luke. This theoretical text is presumed to be a collection of Jesus’ sayings and teachings and was further given credibility with a huge find in Egypt in 1945 near the town of Nag Hammâdi. As the story goes, a local peasant named Mohammed Ali Samman discovered a collection of early Christian Gnostic texts, having stumbled upon several buried jars, all of them sealed. Upon opening the jars the man discovered twelve leather-bound papyrus codices giving birth to The Nag Hammadi library (popularly known as The Gnostic Gospels). Picknett and Prince explain better the importance of the Gnostic texts when they inform:
There are also a large number of fragments of lost works, sometimes referring to sayings or deeds of Jesus that are not in the New Testament, but of roughly the same age. In fact one of the fragments—actually four small scraps of papyrus—in the British Museum and known by the riveting title of ‘Egerton Papyrus 2’ is possibly the oldest surviving document about Jesus in existence.
What is so marvelous about this find is that many of the Gnostic Gospels were dated to roughly the same time as the Synoptic Gospels, the oldest being the Ryland’s fragment of John’s Gospel (circa 125-150 C.E.). The Egerton fragments, a Gnostic text, dated between 90-150 C.E., the same (perhaps older) than the Ryland’s fragment, and shared many of the same verses and sayings of Jesus Christ of the Synoptic Gospels (see: Source criticism and Form criticism), thus proving that a yet undiscovered third source text must exist—this being the lost Gospel of Q. (See: the Nag Hammadi Library)
Another point worth bringing up is that the majority of the Gnostic Gospels show a much more human portrayal of Jesus Christ. In fact, the Gnostic texts such as the Gospel of Mary (attributed to Mary Magdalene) we find no evidence of any miraculous resurrection, which coincides with the original Gospel Mark and its strange absence of a post resurrection Christ. This may suggest that the resurrection story was added later into the canonical scriptures as some scholars suggest.
In his excellent book Jesus and Yahweh: The Names Divine, the literary critic Harold Bloom brings up the most apparent, and regrettably the most ignored, of Biblical changes which should cause us to immediately doubt the divinity of the text as a whole. Bloom’s acute observations lead the scholar to write, “The New Testament frequently is a strong misreading of the Hebrew Bible, and certainly it has persuaded multitudes,” and goes on to inform, “The New Testament accomplishes its appropriation by means of its drastic reordering of the Tanakh.” On the following page Bloom gives a side-by-side list of the book changes of the Old Testament in comparison to the original order of the Jewish Tanakh—i.e. the original Jewish holy book before passionate Christians hijacked and newly reassembled it into what we deem the “Old Testament.”
So regardless of when the Gospels were written, this is important for anyone who is willing to take the Gospel stories for all they're worth, since it appears that much of their composition relies on redaction, or retelling of OT stories re-written for evangelical purposes past the expiration date of Jesus. It basically shows that there is more going on between the lines than most Christians realize.
What may be more shocking to believers is that modern Christianity does not stem from Jesus Christ at all, but rather, comes from that re-envisioned theology of St. Paul. Not forgetting to mention that almost an entire third of the New Testament is Pauline, a fact we can’t afford to overlook, the discerning Harold Bloom mentions, “Between his priority, his centrality in the text, and his reinvention of much of Christianity, Paul is its crucial founder. Yeshua of Nazareth, who died still trusting in the Covenant with Yahweh, cannot be regarded as the inaugurator of a new faith.”
More than this, we cannot neglect the augmentation of Paul’s theology by early church leaders. In the Jesus Dynasty Tabor reminds us, “Although our New Testament gospels contain historical material, the theological editing is a factor that the discerning reader must constantly keep in mind.”
Even the Gospels do not fully agree with one another all of the time, as Bart D. Ehrman puts it, “The biblical authors did not agree on everything they discussed; sometimes they had deeply rooted and significant disagreements.”
Ultimately, this can be troubling for anyone who believes that the Bible is the literal word of God. Robert M. Price, part of the Jesus Seminar, and author of The Incredible Shrinking Son of Man, has equivocated:
The controlling presupposition seems to be, “If the traditional view cannot be absolutely debunked beyond the shadow of a doubt, if it still might possibly be true, then we are within our rights to continue to believe it.” But scholarly judgments can never properly be a matter of “the will to believe.” Rather, the historian’s maxim must always be Kant’s: “Dare to know.”
And this is where I must leave off. Because either you will be contented with what evidence you are given, or you will not, but in the end I hope you follow Kant’s dictum to dare to know. It’s what I have tried to do and will continue to aspire to. As one who is deeply interested, or more precisely: enthralled, by this period of human history I can’t help but find I love to learn about all the theories, the good ones and the bad. Whatever evidence and theories stand up to scrutiny, and are quantifiable, are the ones which are the most stable, and therefore likely justifiable. Consequently, these become the ones I’ll likely settle upon as the best chance of being accurate if not akin to the truth (although as a non-believer and skeptic there is always the possibility to change my mind when better evidence is forthcoming).
I hope this helped answer any questions about when the Gospel books were supposedly written. I wish you good luck and happy researching!
Tristan D. Vick