It seems bogus, because it is. Not the age of layers and how they are determined, but the above analysis of how it is done. The age of layers is determined by radioactive decay. Once you know the age of a layer and find a certain species there and in no other, you can go elsewhere and find that same species and be confident you know the age range of that layer. No real archeologist would say what peach said. That's just BS put out by skeptics to fool the unsophisticated, which apparently you've swallowed hook, line and sinker. Even our resident geologist and skeptic would have to agrree with that, right westwall?
The problem arises when you have nothing to radioactively date. Potassium Argon dating is fairly accurate when you have igneous rock to date. The melt as it cools freezes the isotopes in place and that will give you a very accurate time delineation.
However, what do you do when all of your fossils are in an alluvial or lacustrine (sedimentary) deposit? You will certainly know that the fossils came after the time of the bedrock (which is igneous) which underlays the sedimentary deposit, but that's it. If the fossils themselves are lithified you can once again resort to K-Ar dating (though that results in secondary dating, you are measuring the age of the rock that lithified the bones, the bones themselves were far older) so even when you have excellent markers the dating of fossils can be fraught with difficulties.
Once a particular formation has been dated you can indeed go around the world and date subsequent layers based on those findings (and in fact geologists are trying to do just that) but, there are thousands of areas where you have multiple non conformities and unconformities where you have no igneous formations to use as baselines. You have millions or even billions of years of sedimentary buildups so you know approximately how long a particular geomorphic province has been around but you have no idea of what the ages of the individual formations which make up that province are.
I see no excellent markers in anything the climatologists do. There is no hard/fast data set anywhere. And those that do exist (like the example Ian provided) are corrupted by the climatologists involved.