I think we're talking about Bishop Usher here, who worked out the Earth was created on October 23, 4004 B.C.
Usher worked this out by adding the ages of the various genealogies in the Bible, and there are a surprising large number of people who insist this system is more correct than the 4.5 billion years (+/- 1%) date we have arrived at via radiometric dating and isotope dating of meteorites that stands up to repeated re-testing.
When I say large, obviously relative to the number of people who accept 4.5 billion, it's etremely small, but it's not zero, and consequently, there are a whole raft of pseudo-sceintific methods used by Young Earthers, however, like all religiously-led science, these methods are promoted specifically because they provide evidence that agrees with what the Bible (in this case, via Usher) says. They're also methodologically flawed (because if they did them properly, they wouldn't agree with the Bible at all).