The table below summarises key features: Gastrioceras listeri is a particularly good example of a ZONE fossil.
This is because new sediments are always laid down on top of sediments that have already been deposited.
So, when looking at the history of a cliff face, it is important to read the story it tells from the bottom layer up.
We then describe Grand Canyon rocks as belonging to three “sets,” or packages of rocks, each with unique geologic histories, and present a compilation of “best” numeric ages for Grand Canyon rocks to use when explaining Grand Canyon geology to the public.
Photo 1: Many people consider Grand Canyon National Park the world’s premiere geologic landscape and a “geologic wonder”.
A fossil will always be younger than fossils in the beds beneath it and this is called the principle of superposition.
In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top.
The laws of physics and chemistry that governed geologic processes in the past are the same as those that govern processes now and in the future.
The geologic timescale is a chronology (calendar) of events on Earth based on obtaining ages of past events.
The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.