Actually their argument is that scientists actually have discovered it so it has to be true. Haven't scientists also discovered Noah's Ark though and a bunch of other biblical relics?
Yes, things like evolution and cosmic inflation (i.e. the "Big Bang") are demonstrable scientific truths.
Noah's Ark has not been discovered.
Our faith does not depend on a literal reading of certain portions of Scripture, such as a literal reading of the creation stories in Genesis, or of Noah and the flood.
Our faith depends upon Jesus, the Christ, the Son of God, who suffered under Pilate, was crucified, dead, buried,
and who rose on the third day.
We read and confess the Scriptures because we believe in Jesus.
We do not believe in Jesus because of the Scriptures.
If Jesus is raised from the dead, then He is what He said He was, and our faith is true.
If Jesus did not rise from the dead, then He is dead, and Christianity is meaningless.
It all depends on the truth of Jesus--not on whether or not there was a global flood, a giant boat, or whether there is a literal dome of water over the earth (there isn't) or anything like that.
And those who make Christianity depend on those things, rather than Jesus, are building their faith on weak sand rather than the solid rock and foundation of Jesus Christ.
-CryptoLutheran