Crayon Rock Exercise

“Scientific Method” vs. Geology A forward linear process Includes experiments that are designed to test a hypothesis Experiments are repeated to ensure identical results Geology A backward-looking process No time to run experiments Based on multiple observations and the Principle of Uniformitarianism

Cornerstone of Geology: The Principle of Uniformitarianism The processes we observe in the world produce specific forms in the rocks. These same processes have occurred throughout geologic time, and we can interpret the past by understanding the processes of the present and the rock records they produce. In short: The Present is the key to the Past.

For Example: We know that rivers change their courses, especially during flooding events, forming features known as oxbow lakes. This is an ongoing process that we can observe happening in many places on the Earth today.

Also: Aerial photographs show scars on land surfaces which have the distinguishing features of oxbow lakes, but no longer contain water.

Therefore, according to the Principle of Uniformitarianism: We can conclude that these features were once oxbow lakes, now dried up, but formed by the same processes we see happening in the present. “The present is the key to the past.”

Some important points to remember: The features resulting from geologic processes were the same in the past as we see in the present, BUT…. The places on Earth where they occurred may have been different. The rate at which they occurred may have been different. The intensity which they exhibited may have been different.

When we apply this principle to rocks: We find different types of rocks on the surface and in the crust of the Earth. We see certain processes occurring today that produce these types of rocks. We apply the principle to conclude the same processes happened in the geologic past. We build the geologic history of a particular part of the Earth from the rock record.

What we would like the students to do: Look at our “crayon rocks” Look at the unaltered crayons Determine what processes might have turned the crayons into the crayon rocks Create a “crayon cycle” Given the rock cycle and the definitions of the three types of rock, make analogies from the crayon rocks to real rocks

The Rock Cycle

Igneous Rock A rock that forms from the cooling of molten rock into a solid state.

Sedimentary Rock A rock made from weathered (mechanical/chemical) fragments of rock, consisting of the remains or secretions of plants/animals, or precipitation (from solution).

A rock changed from one form into another by : Metamorphic Rock A rock changed from one form into another by : 1. Intense Heat 2. Intense Pressure 3. Watery hot fluids 2