Planetary Structure Rocks!

What science lets you look at a landscape and see its past? Why, geology, of course. Strictly speaking, geology is the study of Earth’s structures, rocks, and the way they form and change over time. However, the principles of understanding our planet that you learn when you study geology also come in handy when looking at other worlds. So, the earth science we learn in school gives us insight across time and solar system space.

I used to collect rocks as a kid. My first collection disappeared during a move, but that didn’t stop me from picking up more. These days, I have a small collection gathered from my travels from nearly every continent (except Antarctica). Each one has a tale to tell about its origins.

Rock crystal structures fascinated me, which is why I started picking them up in the first place. I noticed pretty quickly the many different shapes and structures in rocks. In 8th grade, we studied geology, which meant taking field trips. Around where I grew up, we were taught early on that millions of years ago, our region had been an ocean environment. Sometimes it was under deep water, and then, as the waters receded, the region was laced with shorelines and marshy areas. Over time, the plant and animal life was buried, and that created coal and natural gas. If you drive along the Front Range of Colorado (say from Pueblo to Cheyenne), it appears as a vast undulating plains area. In my mind’s eye, I can almost see the ocean that used to be there, long before the current Rocky Mountains formed and deformed the nearby landscapes.

A Short History of Colorado Geology

Colorado has been in the making since nearly the formation of our planet. It was once part of the massive continent of Pangaea. It moved around the planet as the plates underlying Pangaea shifted. Colorado’s “basement” rocks date back to that early period. The current Rockies, which are a very recent addition, didn’t even form until after the proto-North American continent had started to take shape.

The story of the landscape I live in exists in the rocks. Those that we see in the Rockies are an open geology book. From Boulder and Denver west, you can drive through broken shards of sandstone, mudstone, and shales, many laid down during the times when this area was part of a great ocean and waterway system. In fact, I-70 cuts through a series of uplifted layers that document those millions of years in geologic time. Very quickly, however, you get to the rocks that flowed once as lava or were heated and cooked by lava to become metamorphic rocks. The central Rockies are made largely of these types of rock.

Then, on the western slope, we get back to the layered sedimentary rocks from the ancient oceans that deposited sediments starting some 500 million years ago. The topmost layers are the youngest and date successively back to the Cretaceous oceans. They eventually drained away as the current Rocky Mountains rose in response to an event called the Laramide Orogeny. It was a period of mountain-building that helped create the Rockies and the larger outlines of the Colorado Plateau. Today I sit on a peak born during that event.

Everybody’s Geology

Your own home region has a geologic past that you can look up and learn from if you wish to understand why it looks the way it does. Mountains, plains, river valleys, islands, you name it, they all have their roots in geologic processes. When I travel cross-country, I often think about what stories the rocks in the flyover states could tell. Or the tales the Appalachians could share. Or the millennia-long legends the rocks of the Himalayas or the Alps could relate.

Applied Geology on Other Planets

The geology of other worlds has another name: planetary geology or planetary science. It lets us apply what we know about how Earth’s geology occurred to explain what we see elsewhere. Mars is a great example of this and we can read its rock record. It has regions that look like riverbeds, lake shore lines, and peaks. Many of the processes that laid down sedimentary rocks here on Earth are (or were) at work on Mars. Clearly, water did some of the work. But, the wind has done so, too, just as it does here at home. We have a few craters on Earth that formed as space rocks slammed into the surface. Mars does, too. As do the Moon, Mercury, Venus, some asteroids, and the icy worlds of the outer solar system. Even distant Pluto has a geological story to tell!

For the rocky worlds (the “terrestrials”) the story really IS in the rocks. Just as on Earth, when I can pick up a rock from the road by my house and understand its story, someday, people will do the same on Mars. The minerals and crystals all have a tale to tell, and it’s one that has been millions or billions of years in the making. That is why I like geology. It uses science to explain the world we live on and the other places in the solar system.