SURVEY NOTES

Can U.S. Interstate Highway 15 Be Used as a Metaphor for Geologic Time?

by Mark Milligan


Simplified geologic time scale with age estimates.

Simplified geologic time scale with age estimates.

We have been asked, “Are all Glad You Asked articles based on actual questions the UGS has received?” No, sometimes the articles answer questions that we, UGS geoscientists, have asked ourselves, such as “what is the best way to visualize geologic time?” Geologic time is immensely deep and sometimes warrants a really big analog to understand it.

It is very difficult to comprehend time spans beyond a few generations, much less thousands, millions, or billions of years. Yet an appreciation of deep time is vital to understanding geologic processes and evolution. One approach to getting a better grasp of the scale of geologic time is to use a time-scale metaphor. Year-long calendars are common metaphors, but distance analogs also work. Students attending the Utah Geological Survey’s Earth Science Week walk along a 216-foot geologic timeline and their reactions at seeing the distance between geologic eras and periods are amazing. But bigger is better for geologic time, so here we chose to use Interstate 15 (I-15) through Utah as a metaphor for geologic time.

From the Idaho border in the north, south to the Arizona state line, I-15 traverses approximately 401 miles across Utah. From its formation to the present day, the Earth is approximately 4.6 billion years old. Using a ratio of 4,600,000,000 years/401 miles: 1 mile equates to nearly 11.5 million years, 1 foot is roughly 2,175 years, 1 inch is roughly 180 years, and the thickness of a penny is approximately 11 years. When driving the 5½ to 6½ hours it typically takes to cross the state, modern humans appear at the last 1 second of your trip! This gives new meaning to kids asking, “Are we there yet?”

All mileage and drive time approximations are from Google Maps.

2002 Utah Winter Olympics Logo.2002 Utah Winter Olympics

Using the 401 miles of I-15 across Utah as an analogy for the age of the Earth, the thickness of two pennies equates to the 22 years that have passed since Utah hosted the 2002 Olympics.

Important

For the safety of yourself and other drivers, never stop on the shoulder of a highway, unless it is an emergency and unavoidable!