Saturday, November 30, 2013

Ancient History in the Rocks

I've been getting a bit more interested in geology lately.  Yes, geology.  Rocks.  The whole idea of how our world evolved, how mountains rose up, went away, and rose up again, with continental plates moving around and grinding into one another, just fascinates me.

I recently read an interesting book titled "The Rocks Don't Lie".  The author, David Montgomery, originally started out to debunk the belief that the world is only a few thousand years old and that all the mountains and everything else were sculpted by Noah's flood.  Those beliefs are, of course, easily contradicted by hard science.  But as Montgomery developed the book, he became more focused on how the back-and-forth between the science of geology and the beliefs of religion actually developed and informed each other over the past few hundred years.  The science that came out of this shows that the Earth has been around for about 4.5 billion years, not just a few thousand.  The science has also shown how our landscape has developed, and continues to develop today.

This was on my mind during my recent trip out west and to the Grand Canyon.  Since the landscape out there is relatively barren of trees, it is easy to see the big picture: big tilted plains, miles-long cliffs where fault lines have broken the surface, canyons where the layers in the rock are plainly visible, extinct volcanos, and lava fields that look like they were laid down last year.  The Grand Canyon itself is an incredible sight, but really, there's interesting stuff to look at wherever you go.  What's also really cool to think about is the same type of layers that are so clearly visible in the Grand Canyon are also below your feet right now.  Our landscape has not been static over the past 4.5 billion years, it has been continually changing.

A while back, I was reading about when and how the Appalachian Mountains were formed.  I knew that these are really old mountains, much older than the Rockies, and that at one time they were supposedly even more spectacular than the Rockies are now.  But what was really surprising to read was that the Appalachians didn't just rise and then be eroded away.  No, mountains have risen here at least twice.  One range rose beginning about 480 million years ago.  It gradually eroded almost completely away and this area became an inland sea.  The current mountains started rising about 66 million years ago.  That, to me, is amazing: plains to mountains to inland sea to mountains again.

I don't have to go very far to see indications of this history.  I just walk out my front door and look at this rock.  We've done some landscaping with river rock that was quarried not far away.  This one was part of the pile.  I got to looking at it one day because it was a bit odd-looking.  I realized that it is actually a rock within a rock.  The white part is an igneous rock, meaning that it was formed from molten rock.  I don't know what it is, maybe a type of granite.  But it was formed under tremendous heat and pressure, meaning it was formed deep in the earth.  Then the land rose until the rock was exposed on a mountain.  It broke off and landed in a stream, where it was eventually rounded into a river rock.  You can see that the edges are all rounded off.  From there, it wound up in sand.  Eventually, the rock and sand were buried under many many layers of other sediments, until it was deep enough that the pressure turned it from loose grains of sand into a rock.  Then the land rose again.  At some point, the sandstone, with the earlier river rock buried inside it, broke loose from a mountain and fell into a stream again.  The stream smoothed it out and rounded the edges.  And then it was picked up by some guys and brought to our house.

Millions of years of history, right here by my front door.  Cool.

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