No evidence, or contradictory evidence?

When confronted with a story that doesn't seem to align with scientific evidence, such as Noah's Ark or the history of the Americas depicted in the Book of Mormon, a common retort is that "absence of evidence is not evidence of absence," i.e. just because we don't have evidence of something does not mean it's not true. In some contexts, this principle is very useful. For example, there's no evidence yet of alien life, but that doesn't mean we know there isn't any.

Here, though, this quote is misused. There's a big difference between absence of evidence and presence of contradictory evidence. To explain, I'll deal with both of these examples individually:

There is no evidence that there was ever a global flood that "destroyed all flesh" as told in the Biblical story of Noah's Ark. But beyond having no evidence, we have clear evidence that refutes this story. Some examples: the Egyptian pyramids, which predate the supposed time of the flood, are undisturbed during the period; tree rings, which keep a precise record of precipitation and can consistently record details of local floods, are also undisturbed; the amount of genetic diversity we observe today could not have come about in only a few thousand years; and, there are simply too many species of animal to fit on an ark for a year (in addition to dealing with logistics like what they would all eat, where their waste would go, etc.)

Thus, not only is there no evidence for a global flood, but any new evidence that could possibly be found would need to account for all of this contradictory evidence somehow. As contradictory evidence amasses, this feat approaches impossibility.

Similarly, with the Book of Mormon: there is no clear evidence that the peoples depicted in the book existed in the Americas. But, there are also anachronisms in the Book of Mormon: horses, wheat, chariots, and dozens of other things that we are quite sure (impossible to be certain, but very, very sure) did not exist at the time in the Americas. We also have the fact of Native Americans' genetic lineage coming from Asia, not Israel. Therefore, previously undiscovered evidence that lined up with the account of the Book of Mormon would also have to account for all of these issues, and many more, before it could be considered convincing evidence of the Book of Mormon's veracity. Even if the dates and population numbers matched up with some known civilization, for example, if that civilization didn't have horses, the Book of Mormon couldn't possible be true, because it contains many accounts of horses being used in battle.

It is difficult, perhaps even impossible, to disprove any of these stories. Then again, it's difficult, perhaps even impossible, to disprove any story that has ever been told: not just from other religions, but all fiction that has ever been written. If I were to say that Lord of the Rings was based on historical fact, you could certainly mount compelling evidence to the contrary, but you could never outright prove me wrong.

So, I guess it comes down to this: I'm as certain that Noah's Ark and the Book of Mormon are myths as I am regarding Greek mythology, Lord of the Rings, and Harry Potter.

If you think there is no evidence of something, but that it could be true anyway, you should double-check to make sure that there's actually no evidence either way. Otherwise, it's possible there's just no evidence that supports your belief, but a lot of evidence to the contrary.

Edit: here's another great post by John D. Cook on the same topic.