Luke 1.70: "As he spake by the mouth of his holy prophets, which have been since the world began."
Here St. Zacharias praises God at the naming of his son, John.
I think this is a proof-text on several scores. First, there are no prophets without a church. Thus, God has always had His people, and His church has existed since the beginning of time. We're specifically told (Matt. 23.35, and Luke 11.51) that Abel is a martyr, and I'd argue that Adam was likewise a prophet who taught his family the ways of God. This is illustrated especially in Gen. 4.1, when Eve welcomed Cain's birth as a messianic sign.
Second, if there are prophets from the time the world began (the Greek is "eon"), it follows that there are no long periods of time without humanity. This isn't a primary argument for creationism, but it certainly seems like a supporting argument.