Cross cutting relationships used relative dating

For example, the principle of superposition is based, fundamentally, on gravity.

In order for a layer of material to be deposited, something has to be beneath it to support it.

For example, lets put the following movies in order of relative age from oldest to youngest: Twilight, Finding Nemo, the Avengers, the Hunger Games.

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.

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

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).