I cant remember the sight,possibly something like Ripleys believe it or not,but I remember seeing examples of bodies being disentered that were only 50 years in the ground,totally fossilized.I think they were in some area where the water level could enter the caskets and was highly mineralized.
Anyway,If tests were done,the minerals would show ages of millions of years but the tombstones proved otherwise.
There ware also some blind radiometric age dating tests done from Mt St. Helens 1980 eruption that indicated millions of years.
Part of the reason the did those tests was due to the fact that MSH resembled the sedimentary layering found throughout the world.
google polystrate fossils for more age-dating problems not to mention the wolemi pine tree.
There are several different ways to 'date' a rock layer, the most common is relative age the attribution of a rock layer to a time period based on its placement relative to the rocks around it. The next, dealing with fossil content is a biostratigraphic age, with certain assemblages of remains being ascribed to a certain time period, and then the numbers ("absolute age") come from interpretation of isotopic dating of minerals in igneous and or metamorphic rocks (in the latter case, identifying their last period of high temperature/pressure deformation) which are sandwiched in, buried under, intruded into, or provide the materials for sedimentary rock in which fossils are found. Inferences are made about the age of the sediments according to their stratigraphic relationships to the rocks for which an absolute age has been acceptably established.
The numbers can be suspect for sediments, as a given rock formation is generally assumed to have the same age over its lateral extent when the environment in which it formed may have shifted geographically over time, they are usually given as a range of dates. There are few markers which are global in extent (one such is the K-T Boundary--the sediment from the impact event which has been credited by some with the demise of the dinosaurs), so there are places where the record doesn't completely flange up, or absolute ages may be in dispute, even within the framework of isotopic dating.
Regardless of the numbers which have been attached, this makes a good working model to designate relative ages of strata and sort things out.
Whether the numbers are absolutely correct depends on measurement, sampling, and on the constancy of physical constants.
If the universe is 'billions' of years old, we don't have enough data on physical constants to determine how constant they really are over time.
Anyway, in our efforts to understand that which surrounds us, we do come up with working models, with apparent rules, which are subject to constant revision because no matter how much we know, for every answer, we commonly end up with more questions.
The fundamental assumption in this modeling is that the same forces which are working now work in the the same way now as they did then, and, of course that they worked at all.
Again, we assume this to be the case, because it makes for a nice, tidy working model.
Yet at the same time, if we are ever to travel among the stars, we will have to find ways to exceed the parameters we have set in our interpretation of nature, and we are actively seeking ways to do so, looking for the faster than light particle, the wormhole to transit normal space, and ways to harness or negate the effects of gravity, for a few.
So despite placing certain rules on the physical universe, we seek to transcend those rules ourselves. So I don't have any trouble with an all-knowing and all-powerful God who can transcend the rules we have imposed through observation of how things seem to work at the moment--or even over the past few hundreds of years.
For now we see as through a glass, darkly...