More than three quarters of all exposed rock on the World is sedimentary, i.e., it was laid down under water and then dried out (this is basically true whether the rock is further classified as being clastic or chemical).
Geology links certain rock strata with periods of time and assigns to each stratum a name, such as, 'Precambrian', 'Cambrian', 'Triassic', 'Jurassic', 'Cretaceous', and so on. Some strata are often rich in fossils (Cambrian is a good example of this). Using the fact that certain naturally-occurring elements (referred to as a 'parent') undergo radioactive decay into other elements (referred to as a 'daughter') in a time which can be determined by laboratory experiments, various absolute dating methods have been developed, including carbon-14 (for which Willard Libby won the 1960 Nobel Prize for Chemistry), potassium-argon, rubidium-strontium, etc.
However, because of such things as uncertainties in the original composition of the rock when it was being laid down, and addition or subtraction of parent or daughter elements since, radiometric dating is notoriously unreliable when it comes to sedimentary material. Instead, sedimentary rocks are usually dated by recourse to the fossils they contain. If the age of the fossil is known, and the fossils were buried in the stratum, then we must know the age of the rock, right?
Wrong, because the fossils are dated by seeing what stratum they were discovered in. To illustrate, let us assume that a particular fossil is 40 milliard years old (it won't matter that this is older than the supposed age of the universe, since we are told that some stars are older than the universe!). Where was it found? Let's say in the Cambrian. We deduce, therefore, that the Cambrian is 40-milliard-year-old rock. Since it is 40 milliard years old, any fossils it contains will be around this age. So we conclude that our original estimate was correct! Such circular reasoning is the essence of sedimentary strata dating. Think of a number, any will do, quickly double it and add on ... oh, three and a half milliard.
Even in those cases where radiometric dating is claimed to be accurate, namely igneous rock, there have been some pretty spectacular faux pas, such as ages ranging from about 140 million to 2.96 milliard years for samples distributed to twelve different laboratories, taken from the Kaupelehu lava flow, Hualalai volcano, Hawaii. However, these supposedly 2.96-milliard-year-old rocks were formed when the volcano erupted in 1800/01.
Similar ludicrous figures of several milliard years were obtained from samples that solidified after the Mt. St. Helens eruption on 18th May, 1980.
Mt. Rangotito on North Island, New Zealand, buried trees when it erupted. The age of the trees, using C-14, was analysed at 225 years. The age of the overlying, solidified rock, using K-Ar, was given as 465,000 years.
These are just a few examples of 'accurate' radiometric dating methods giving totally absurd results. How do we know that any dates produced by such techniques are correct? Simple, those that support popular ideas, like organic evolution and uniformitarian geology, are accepted, and those that do not are rejected.
In order for the dating laboratories to be spared any future embarrassment from Creationists, no sample is now accepted without an accompanying form, specifying exactly where the sample came from. This allows samples to be tied in nicely with the paradigm, and science to remain above reproach. (A similar approach is taken to hide the lack of real science in the 'Global Warming' scam.)
It is a very common misconception that the rocks we see all around us took millions of years in the making. The fact is that rocks can be formed in a few hours or days, requiring only sediment, water and a cementing agent, rather than great lengths of time. Furthermore, the 'strata' exposed in rock faces all over the World give no indication of age. For example, the Mt. St. Helens eruption of 1980 produced 600 feet of new 'stratified' rock in a matter of hours.
The events which followed the eruption of this particular volcano produced evidence before our very eyes of the processes that would have occurred on a massive scale after a cataclysmic flood. One of these events was the phenomenon of lake outflow with sediment loads.
There is evidence to suggest that a great lake was left in place over a sizeable part of North America as flood waters abated upon the World. When the retaining wall was breached, the rapid and enormous outflow from this lake resulted in what we now call the Grand Canyon. Again, just such a process was witnessed at Mt. St. Helens, when flowing water and mud gouged out a mini (by comparison) canyon, 200 feet wide and 100 feet deep.