# Time & Landscape

News Flash! When it comes right down to it, landscape development is all about time. While water, ice, wind and plate movements carve out the hills and valleys outside our windows, time is the key factor. How long do you think it took for the U-shaped valley at the beginning of this module to form?

Weathering, erosion and plate tectonics create landforms at rates that are too slow to observe over time periods that are too big to easily comprehend. The bottom line is that the landscape we see has been forming very slowly for thousands to millions of years.

How slowly? Here is an example: Dixon Peak, west of Dell, is on the uplifted side of the Red Rocks Fault shown in the Lima Valley landforms example. The top of Dixon Peak is 2939m high, and Dell, in the valley, is 1834m high. Geologists studying the history of SW Montana have concluded that the two were at the same elevation just 4 million years ago.

A room full of geologists would say “Holy cow! That’s fast!” if they were told this, but a passerby would probably not be equally impressed with this rate of action. What is the rate? The motion was (2939m – 1834m) = 1096m in 4 million years!

For reference, your fingernails grow about 30mm (3cm) each year. You don’t see it happening, but you notice from time to time that it is time for a clipping. Likewise, we don’t usually see our landscape forming, but every hundred or thousand of years you might notice that things have changed.

So Dixon Peak has been moving upwards with respect to Dell at about a quarter of a millimeter each year – on average. It is likely that movement did not occur at a steady pace, though, and that strain stored up on the fault for hundreds or thousands of years until, WHAM!, there was an earthquake and the fault moved a meter or two very rapidly.

Check Your Thinking:  If the average movement is 0.25mm/year but the fault really moved in 1m increments every so often, causing periodic earthquakes, what was the average time between earthquakes?

There are a number of ways to try to grasp the enormity of geologic time, and the slow, slow rates at which geologic events occur. Perhaps one of the best is to create analogies or metaphors for rates and times. For instance, comparing the rate of a geologic process to the rate of fingernail growth, or comparing the age of the earth to the length of a football field. One easy thing to do with children is to create a geologic timeline out of a roll of toilet paper, as described on this Toilet Paper Timeline website.

This interactive online calculator, Comprehending Geologic Time, allows users to create analogies for the age of the earth.

The National Science Digital Library also offers this comprehensive list of online resources for teaching geologic time.

The MSP project is funded by an ESEA, Title II Part B Mathematics and Science Partnership Grant through the Montana Office of Public Instruction. MSP was developed by the Clark Fork Watershed Education Program and faculty from Montana Tech of The University of Montana and Montana State University, with support from other Montana University System Faculty.