Second, it is possible to determine the numerical age for fossils or earth materials.Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time.Third, magnetism in rocks can be used to estimate the age of a fossil site.This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.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.This is the principle of original horizontality: layers of strata are deposited horizontally or nearly horizontally (Figure 2).
Accordingly, the oldest rocks in a sequence are at the bottom and the youngest rocks are at the top.
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
Younger layers are deposited on top of older layers (principle of superposition).
" 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.