The answers to most of these questions differ by billions of years.
Ask your colleague teaching history: She or he can tell you students have difficulty conceptualizing and contrasting the different historical eras, such as the medieval period in Europe and the colonial period in America.
However, to many middle school students, these answers boil down to variation on a single theme: really old, a long time ago, and for a long time.
Watch this video to find out how we use index fossils to establish the relative ages of rocks.
In previous lessons, we talked about the Geologic Time Scale and how scientists use it to piece together the history of the earth.
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.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.
Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
The Earth and Space Science content standards, grades 5-8, of the National Science Education Standards include: Structure of the earth system; Earth's history; and Earth in the solar system; none of which can be mastered without good conceptual understanding of geologic time.