Skeptics claim that there's no way Noah could have fit all the animals on the ark. Michael Shermer, a self-proclaimed atheist, the publisher of Skeptic Magazine and director of the Skeptics Society, is quoted as having said:
There’s no possible way that Noah could have retained all 10 billion species on a single boat and then distributed them appropriately where the marsupials are all in Australia and so forth. This is ridiculous. It is so ridiculous I find it embarrassing for people who attempt to prove that it's true.
We actually agree with Shermer that it would been impossible for Noah to have taken every known species (10 billion, according to Shermer) onto the ark. But let's look at the plan God had and what He told Noah to do. This will answer the skeptics claims.
"And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind..." (Genesis 1:21)
"And God made the beast of the earth after his kind, and cattle after their kind, and every thing that creepeth upon the earth after his kind ..." (Genesis 1:25)
Genesis tells us that God created land and sea creatures after their kind. Kind is not the same thing as species. It's closer to what biology calls families, with some exceptions. Take for example, the "dog" kind. One female dog and one male dog can mate and produce various species (e.g. coyote, wolf, and all domestic dogs). So the different species we have today could have easily been generated after the flood from the information already present within the parent kind. A plain reading of the Bible teaches that Noah only had to take representatives of the different kinds of land-dwelling, air-breathing animals.