Most Gospel Jesus-biography have a pre-history of being orally recited and passed down.
A full page will analyze these evidences:
This is relevant because it means that the content pre-dates Mark (and any form of Q used by Mt and Lk), so it pre-dated AD 70, plausibly by a lot.
Rather than inventing Jesus-biography, the authors of Matthew, Mark, Luke, and John—as editors/redactors—were honest in writing their Gospel reports.
**This page analyzes 4 arguments:
This is relevant because the events that the Gospel authors got witness approval on were incredible events that the witnesses perceived and remember (i.e. content) as dating back to Jesus’ life around AD 30. Their perception and testimony, and therefore the tradition itself, date to AD 30. (The authors would not have accepted content that did not have a reputation for being connected to a witness who would’ve seen/heard Jesus in c. AD 30).
The Gospel stories are often quite “dissimilar” to the AD 31-90 church; i.e. they display behavior and language which was discontinuous with post-Jesus beliefs, expectations, styles, preferred vocabulary, background, understanding, natural authorial intent, and so forth.
The page analyzes 3 arguments:
This is relevant because it was dissimilar to Christianity in virtue of predating Christianity (i.e. predating Easter).
We discern an Aramaic original behind the recorded-in-Greek teachings of Jesus in the Gospels.
This page looks at 3 arguments.
This is relevant because it suggests the content started in Aramaic, and later became popularized in Greek as recorded in the Gospels. This sort of change usually (but not always) takes time. (And as a very small side-point: content developed at a later time would more likely have been formulated in Greek from the start.)
[Brackets] mean "forthcoming."