Verification and falsification

Our tests showed that if the asteroid hypothesis were true, it would explain our observations: the fossilised dinosaur bones in rock strata up until the end of the Cretaceous period, but not after; the absence of many other types of terrestrial and marine fossils after the end of the Cretaceous period; high iridium levels in rock strata at the boundary between the Cretaceous and the Tertiary periods. If the hypothesis had failed those tests, we’d know that it was false. We cannot say definitively that it’s true, however, just because it passed them. The tests show that if the hypothesis were true it would explain the observations, but they do not show that those observations would be explained only by the asteroid hypothesis. That’s the distinction between verification, showing something to be true, and falsification, showing something to be false. That’s why we have to avoid the fallacy of affirming the consequent. And that’s why we remain open to other possibilities.