From the beginning of this course, we have stated that the Earth is about 4.6 billion years old.
How do we know this and how do we know the ages of other events in Earth history?
Prior to the late 17th century, geologic time was thought to be the same as historical time.
With a rock record that spans more than 1500 m.y., Grand Canyon is truly a panoramic view into the geologic past.
Geologists still use Steno's principles, with some refinements and additions.
They are summarized as the Principles of Relative Geologic Age Determination, sometimes referred to as the Principles of Relative Dating.
The Grand Canyon landscape is geologically young, being carved within just the last 6 m.y.
There are younger geologic deposits in Grand Canyon too, such as the Ice Age fossils found in caves, a 1000-year-old lava flow in the western canyon, and even the debris flow deposits that continue form each year.