This section discusses the methods geologists use to determine how old a fossil or rock is. Therefore, the sedimentary rock must be older than the intrusion.
Relative age-dating methods determine when an event happened compared to another event. Geologic time scale Relative age-dating involves comparing a rock layer or rock structure with other near-by layers or structures. Roadcut in Wise County showing the principle of superposition (Photograph by Stan Johnson) Flat-lying sedimentary layers from the Appalachian Plateaus province of southwestern Virginia illustrate the principle of superposition.
These are the surfaces that we can get absolute ages for.
For the others, one can only use relative age dating (such as counting craters) in order to estimate the age of the surface and the history of the surface.
The textbooks speak of the radiometric dating techniques, and the dates themselves, as factual information.
Far from being data, these dates are actually interpretations of the data.
The biggest assumption is that, to first order, the number of asteroids and comets hitting the Earth and the Moon was the same as for Mercury, Venus, and Mars. The bottom line is that the more craters one sees, the older the surface is.
This can be interpreted in two ways: why it is important to know the age of a planet or how is age dating important in determining the age of a planet?
Using these methods, geologists have created a geologic time scale for organizing past times in earth’s history. We can get absolute ages only if we have rocks from that surface.For others, all we are doing is getting a relative age, using things like the formation of craters and other features on a surface.The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.As it is free swimming it could have travelled a considerable distance.These ages have been derived from relative dating and absolute dating (radiometric dating) of rock layers and fossils.