Plate Tectonics: Global Thermostat

Question: Why do you believe life may be exceptionally rare in the universe?

Peter Ward: Well, when we thought up the Rare Earth Hypothesis, it was simply taking a look at what happened on this planet that allowed us to have multi-cellularity. Part of it was that we had conditions allowing habitability for billions of years. It took a long time to get to something as simple as a two-celled creature; a long time.

How do you get a long time? You do it because system of temperature, systems of oxygen, systems of all the gasses and the carbon movement remains stable. If you get too hot, too cold and only a little bit to hot and a little bit too cold on a planetary sense, you can kiss it all good-bye. So, what is it about the earth that allowed those things to continue for such long periods of time? The most important is plate tectonics. This is the movement of the surface of the earth over the top of a mobile softer rock substrate beneath it. So, the continents skate around like bumper cars. The part of that process is a continental and ocean recycling. And that recycling system is inherently – is the absolutely necessity to keep a long term temperature constancy. We have this feedback system, a thermostat system. What makes the earth warmer is carbon dioxide, what makes the earth cooler, interesting enough is the removal of that carbon dioxide. Volcanoes put it in the air, but weathering removes it. If you take a granite, or any rock that had a volcanic material in it and let it chemically weather, one of the byproducts takes Co2 out of the atmosphere. The warmer it gets, the faster that process works. So, the warmer it gets the faster the breakdown removes Co2. If you get down to an area, or a level at which you can no longer chemically weather the volcanoes refill you up. Now that bang, bang feedback system has been in service for over 3 ½ billion years or more. That has kept us at a stable temperature.

The continental game of bumper cars known as plate tectonics is part of a global recycling system crucial to maintaining long-term temperature constancy—and giving rise to life.

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