The principle of superposition therefore has a clear implication for the age of a vertical succession of strata.
The most common rocks observed in this form are sedimentary rocks (derived from what were formerly sediments), and extrusive igneous rocks (e.g., lavas, volcanic ash, and other formerly molten rocks extruded onto the Earth's surface).
The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy".
My thanks to both him and other critics for motivating me.
Much of the Earth's geology consists of successional layers of different rock types, piled one on top of another.
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).