Ask them how BILLIONS of species could fit into one arc with enough people to re-populate the world. Can anyone say lions, tigers and bears, oh my?
There is not enough water on earth for a global flood.
guys...youre forgetting.. those challenges are answered by: "With God all things are possible." thus it nets nothing.
Only evidence, physical, observable, scientifically evidence refutes mysticism and faith. Why play into their hands if you dont have to: SHOW ME THE FUCKING WOOD REMAINS SO WE CAN TEST IT'S ORIGIN, AGE, AND NATURAL OR MANSHAPED PROPERTIES.
The shortest path - ask for a reasonable accounting for "rules of evidence" for biblical remnants. Take those rules and ask to introduce your own evidence. Why include the remains of the ark but exclude archeological digs (visible in principal within the decade, on Google earth) around Sumerian grain silos that predate Adam and Eve and their special garden? Can we apply these rules to include bone flutes from 35,000 years ago? How about stone axes from Homo Habilis?
Then point out that the "gaps in the biblical record" prevent you from accepting the Theory of Bible. Ask why the remains of a crocoduck was not next to the remnants of the ark. Try to find out if Ray Comfort's modern day banana was on the ark.
A true fundamentalist must reject all physical evidence and instead rely on faith alone. Point this out until they kick you in the nads.