Somewhere in Time

7/23/06 – 7/29/06

by C. Zaitz

A single glance at the night sky can transport you back in time. The stars are very far away, and their light takes time to travel to us. Even the bright, steady light from Jupiter takes about a half hour to reach us. Starlight can take hundreds or even thousands of years to reach us. I realize that on the scale of our galaxy, which is what we see when we look at the night sky, a human lifetime is pretty short. But my recent week-long foray into geology of the Badlands and the Black Hills of South Dakota and Devil’s Tower in Wyoming left me feeling downright ephemeral. I was looking at rock formations billions of years old. I use the word “billions” all the time when talking about numbers of stars or distances to far away galaxies. But touching rocks that had been buried for billions of years and are now exposed and blowing away in the wind was something different.

The Earth is old, about 4.5 billion years old. The Badlands aren’t quite that old. About 70 million years ago, the rising Rocky Mountains and Black Hills dusted the lands to the east with sediments and sands. Back then the whole middle part of North America was covered with a warm, shallow sea. The sea grew and shrank over time. Dead sea creatures and dust built up layers of limestone, sandstone and clay sediments. Then, a few million years ago, the area of the Badlands began to rise, exposing 70 million year old sediment layers to the wind and rain. Once the clay and sand layers were dissected by rivers, the erosion process took over and created the incredible display of “badlands” that we see today. Hidden in the soft clays are fossilized bones of creatures that used to roam the Earth, such as the gigantic-headed Triceratops and three-toed horses that were smaller than Great Danes.

The granite intrusions of the Black Hills and Devil’s Tower are even older. They are Pre-Cambrian, at least 570 million years old, most likely over a billion years old. But some of the oldest rocks I touched were in Sioux Falls, South Dakota. The pink quartzite found there used to be sand 2 billion years ago. Time, tide and great pressure and heat formed the sand into rock. The rock was hidden for billions of years by layers of sediments, and now has been exposed to the elements through erosion.
Some of the quartzite ended up in the local roads, giving them a particularly curious deep pink color. Both the quartzite and the gas we were combusting in the mini van have been hidden deep in the earth for ages, but now we’re using these resources up in a matter of decades.

I touched some really old rocks, but the Moon showed us the most ancient rocks we can see. I was annoyed at Luna for spilling her light over the night sky all week long. She washed out any chance of seeing a dark star-lit sky. But the 4 billion year old surface of the Moon reminded me of how old things are, and how we are just here briefly, somewhere in a long continuum of time.

The class was taught by Dr. Murray of the University of Michigan at Dearborn. It was an excellent class, and has forever changed the way I look at rocks. And now I don’t feel so old anymore!

Until next week, my friends, enjoy the view.