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Much of the Earth's geology consists of successional layers of different rock types, piled one on top of another.

his document discusses the way radiometric dating and stratigraphic principles are used to establish the conventional geological time scale.It is not about the theory behind radiometric dating methods, it is about their , and it therefore assumes the reader has some familiarity with the technique already (refer to "Other Sources" for more information).They are the "initial working hypotheses" to be tested further by data.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).This document is partly based on a prior posting composed in reply to Ted Holden.

My thanks to both him and other critics for motivating me.

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.

However, note that because of the "principle of cross-cutting relationships", careful examination of the contact between the cave infill and the surrounding rock will reveal the true relative age relationships, as will the "principle of inclusion" if fragments of the surrounding rock are found within the infill.

Cave deposits also often have distinctive structures of their own (e.g., spelothems like stalactites and stalagmites), so it is not likely that someone could mistake them for a successional sequence of rock units. Each of them is a testable hypothesis about the relationships between rock units and their characteristics.

Geochronologists do not claim that radiometric dating is foolproof (no scientific method is), but it does work reliably for most samples.