The first thing to note is that the Bible isn’t a source of science or history as we know it, but of religious truth. As John Paul II once observed, “the Bible does not show us how the heavens work, but how to get to heaven.”
This is particularly true of the stories in the book of Genesis, which deal with the very beginning of the world down to the time of the patriarchs (about 1500 B.C.). These accounts began as folk stories that were edited and adapted and then woven together by later authors during the time of the kings of Israel and Judah (much, much later than the period in which the stories take place). The purpose of the book was to describe God’s relationship with the human race before the time of Moses and the origins of a Jewish people.
There are ancient accounts of a great flood from Mesopotamia that show similarities with the Genesis story of the flood. Perhaps the terrible floods that were a frequent occurence in that part of the world helped stimulate human imaginations to create a story about an “ultimate flood” that brought about a renewal of the human race and the beginnings of a covenant between God and people. In the times during which the flood stories were conceived, people didn’t have a sense of “the whole world” as a spherical planet revolving around the sun. The “world” was the land which they knew, ending at whatever bordered it. A major flood could easily seem to be “the end of the world.”
The story of the flood in the book of Genesis contains much religious insight, such as the terrible consequence of sin, the power of a single just person to bear God’s hope to a hopeless situation, the faithfulness of God toward creation, God’s life-giving intentions toward the human race symbolized by the beauty and wonder of the rainbow. It shows that the covenant God eventually made with the Jewish people had its roots in the covenant relationship which God desired with all creation.
Catholics do not take the story of Noah and the flood as literal history. There is no true evidence that there was once a flood that covered all the earth or that the human race “re-began” from Noah and his family. But we believe in the God of hope and new beginnings which the story reveals.
A good book which goes into some detail about the writing of the book of Genesis is Reading the Old Testament: An Introduction, by Fr. Lawrence Boadt, C.S.P. (Paulist Press, 1984).