There's another interesting implication of a 6000 years old earth.

The way radioactive dating works is that we know the decay rate of specific radioactive substances. For example, uranium decays to lead with a known half life of either about 4.5 billion years (u238 to pb206) or about 700 million years (u235 to pb207). We know this because we can observe the half life of uranium in a laboratory, and we can observe the stages of decay until it eventually becomes lead and, with that, stable. We know exactly how uranium decays.

With his knowledge we can then look at substances like e.g. zircon that we find in ancient rocks. Zircon is a fairly common mineral that can include uranium in its crystal structure. It cannot include lead. Therefore, when we find zircon with embedded lead, that lead must be the result of uranium decay. We can determine the ratio of uranium to lead in our sample, and from this we can know how much uranium was there initially when the crystal was formed, and how much of it decayed since then. Since we know the half life of uranium, we know how long this would have taken, given the observable modern day decay rate of uranium. This is just one example of radioactive dating, but they generally work like this.

So what is the key weakness of radioactive dating? Right, we just assume decay rates haven't changed. There are good reasons for assuming this. We can, for example, observe how decay rates change with changing environmental conditions. There are some experiments that suggest only very small changes in those specific cases that are interesting for dating. We can look at light that reaches us from distant stars to find out if decay rates were different in a younger universe. For example, some supernovae exhibit a decay in luminosity that can be directly linked to the radioactive decay of nickel. The farther away such a supernova is, the farther back in time we can know the decay rate of nickel. So we can actually be fairly certain that we're right about radioactive dating. There are ways to prove it wrong, but so far, we've failed to do that because all the evidence seems to indicate it's a good model and that it works.

But that's not what I'm getting to. Let's, for a second, give the Young Earth guys the benefit of the doubt and assume that we're wrong about the age of the earth, that radioactive dating is broken, and we all made a huge mistake. Because all these observations that the 4.5 billion year figure comes from are observations that were made in modern time and can be repeated at any time, radioactive decay must still have happened. Except if the earth is only 6000 years old, it happened at least about seven hundred thousand times faster, but actually faster in the past, since we know it's not that fast now.

In other words, a 6000 years old earth was really radioactive back when the guys mentioned in the Bible lived. They were all freaks. If there was a Fallout game based on the Bible, you'd shoot them.

(Of course, Young Earth Creationists will just say that God put stuff there to confuse us, but I think it's still funny.)