Isotope dating techniques
his document discusses the way radiometric dating and stratigraphic principles are used to establish the conventional geological time scale.
Using these principles, it is possible to construct an interpretation of the sequence of events for any geological situation, even on other planets (e.g., a crater impact can cut into an older, pre-existing surface, or craters may overlap, revealing their relative ages).Most of these principles were formally proposed by Nicolaus Steno (Niels Steensen, Danish), in 1669, although some have an even older heritage that extends as far back as the authors of the Bible.A few principles were recognized and specified later.There are situations where it potentially fails -- for example, in cave deposits.In this situation, the cave contents are younger than both the bedrock below the cave and the suspended roof above.The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy".
Fundamental to stratigraphy are a set of simple principles, based on elementary geometry, empirical observation of the way these rocks are deposited today, and gravity.
The simplest situation for a geologist is a "layer cake" succession of sedimentary or extrusive igneous rock units arranged in nearly horizontal layers.
In such a situation, the "principle of superposition" is easily applied, and the strata towards the bottom are older, those towards the top are younger.
Geochronologists do not claim that radiometric dating is foolproof (no scientific method is), but it does work reliably for most samples.
It is these highly consistent and reliable samples, rather than the tricky ones, that have to be falsified for "young Earth" theories to have any scientific plausibility, not to mention the need to falsify huge amounts of evidence from other techniques.
For example, the principle of superposition is based, fundamentally, on gravity.