Remember that the rocks were deposited originally on a horizontal surface (or nearly so) so if they are no longer horizontal then something had to happen to them.
If there is an unconformity then work on the oldest event up to that unconformity because this represents a break or a gap in the rock record.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.
You will join the unconformities by linking them with periods of uplift and erosion followed by ocean rising and deposition of sedimentary rocks (if the rocks are marine in origin.
Unlike people, you can’t really guess the age of a rock from looking at it.
Yet, you’ve heard the news: Earth is 4.6 billion years old. That corn cob found in an ancient Native American fire pit is 1,000 years old. Geologic age dating—assigning an age to materials—is an entire discipline of its own.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.
To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.
There are two basic approaches: relative age dating, and absolute age dating.
Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you.
This activity was selected for the On the Cutting Edge Exemplary Teaching Collection Resources in this top level collection a) must have scored Exemplary or Very Good in all five review categories, and must also rate as “Exemplary” in at least three of the five categories.
Usually this exercise is associated with a cross section or profile in which there are a series of stacked rock units composed of sedimentary, igneous, and/or metamorphic rocks as well as structures such as faults and folds (anticline, syncline) and unconformities (nonconformity, angular unconformity, If you have subsequent deposition of marine sediments (limestone, shale and sandstone) then the land mass must subside or the oceans rise to cover the surface by water before you can have deposition of sediments.