Note: This program first aired on February 2, 2013.
Imagine if we could peel the Earth like we peel an orange. The outer skin of the earth is made up of rigid plates of rock. These plates fit together in a spherical puzzle, just like the pieces of orange skin, if we were nimble fingered enough to put them back together. The spherical puzzle is where the Earth as orange analogy ends however, because the plates that make up the surface of the earth are constantly remaking themselves, changing shape and moving around, in ways the skin of an orange can only dream of.
The study of these plates and their movement is the field of plate tectonics, a branch of science that didn’t even exist until the mid 20th century, though the recognition that the landmasses of the Earth, while separated by oceans, seemed to fit together existed as soon as the world was mapped.
Plate tectonics works because of the anatomy of the Earth. The outer most layer of the Earth is called the crust, and is composed mainly of silica, oxygen and a few heavier elements like iron and magnesium, in the forms of granitic and basaltic rocks. The crust is relatively light, having a lower density than the underlying rocks that make up the deeper tissues of the Earth, the mantle and the core. The rocks directly below the crust are rocks by chemistry only, behaving more like silly putty than the solid bedrock we are familiar with. The light crust literally floats on the denser material below, and because that material is somewhat plastic, it deforms when force is applied to it, and flows slowly, much like a glacier flows, seemingly solid, but constantly moving.
Just like the pieces of peel from an orange, the crust of the earth is broken into discrete chunks, or plates. They slowly drift around on the surface of our sphere, grinding past each other causing earth quakes, smashing into each other causing mountains to rise up where none were before, and diving back down into the hot depths of the inner Earth, where they are heated and melt and eventually rise back towards the surface as the material of volcanoes. Understanding the movement of the plates has provided humanity with an elegant and overarching set of explanations for many of the shapes and forms we see on the landscape around us every day.
What we think of as permanent and unchanging space is really a dynamic mosaic, albeit one that changes at a pace we cannot comprehend. The cleverer of us have learned to read the signs of that slow motion dance on the land, while the rest of us persist in our dream that what we see around us is what has always been, and what will always be.
References:
I don’t generally direct people to Wikipedia (primarily and admittedly due to my own academic snobbery), but in this case, the Plate Tectonics entry is actually quite well done http://en.wikipedia.org/wiki/Plate_tectonics.
Those folks at UC Berkley have done it again…animations! Interactive maps! http://www.ucmp.berkeley.edu/geology/tectonics.html
Here’s a lot more info from the University of Texas at Arlington—including plate tectonics stuff you can put on your Ipad, http://www.scotese.com/
