The Word of God revealing Himself to His People
through
the sacred authors was first of all oral. Periods of
oral
transmission varied.
The revelation of Genesis, from prehistory to the
time of Moses
is an example of oral transmission.
The period from the resurrection and ascension of
Jesus
(about 30 AD) until some of Paul's letters (about 51
AD) or
the writing of the first Gospel, Mark's (about 65
AD), is another
example of oral transmission of revelation.