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geologic time

What is a Rock?

The word rock means different things to different people. As with many words, its scientific meaning is different from many of the meanings used in everyday language, so lets start with a short video on the scientific definition of a rock.


I took this photo near the entrance to Arches National Park. What geologic structure shaped the rocks of this park?


This is Oak Tree House at Mesa Verde National Park, built by Native Americans in the year 1250 A.D. They left no written records, and no verbal history survived, so how do we know so precisely when it was built?


Many of the bluffs here have layers of sandstone that tilt up and down at different angles. What caused that?


These fossils of dinosaur tracks near Tuba City , Arizona are thought to be from Dilophosaurus. In the movie Jurassic Park, Dilophosaurus was the small dinosaur that had a frill on its neck and spat poison. Actually they grew up to 20 feet tall, and we have no evidence of either frills or poison. For size reference, the black object is my cell phone. Still, this dinosaur fit better into the movie than most of the others featured. Why?


I took this photo during a visit to Bryce Canyon National Park. What special erosional conditions formed these amazing rock structures?