2 types of radiometric dating
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
The study of strata is called stratigraphy, and using a few basic principles, it is possible to work out the relative ages of rocks.
This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks." First, the relative age of a fossil can be determined.Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.This is the principle of original horizontality: layers of strata are deposited horizontally or nearly horizontally (Figure 2).
Thus, any deformations of strata (Figures 2 and 3) must have occurred after the rock was deposited.
Most sediment is either laid down horizontally in bodies of water like the oceans, or on land on the margins of streams and rivers.