The date was February 22, 2007. The event was a NASCAR race at California Speedway in Fontana, CA. I stood in the stands with my oldest son as the green flag dropped. As the collective roar of 32,250 horsepower barreled down upon us, I stood amazed at how physically impacted I was—considering I had not moved. In fact, I find it difficult to communicate just how forceful a NASCAR race is to those who have not experienced one firsthand. However, regardless of the power delivered by these finely tuned machines, each car would stop rather abruptly without an efficient lubricant making sure all the engine parts glide smoothly past one another.
While motor oil fills the bill for race cars, another liquid provides the lubrication for immensely more powerful motions throughout Earth. It is well known that liquid water acts as the ideal medium for life-essential biochemical reactions. Consequently, the discovery of a planet that might contain liquid water generated great excitement in the scientific community. However, a growing body of evidence demonstrates how water also works to maintain the critical process of plate tectonics 4.5 billion years after Earth's formation.
As described in Peter Ward and Donald Brownlee's book Rare Earth, plate tectonics generates and renews the continental landmass, which houses the vast majority of Earth's biodiversity. Additionally, tectonic activity acts as a global thermostat—ensuring abundant liquid water oceans—by regulating greenhouse gases such as carbon dioxide. In a recent Connections article (Quarter 3, 2007, page 4), I described a discovery showing how the unusual interaction of water and minerals just below Earth's crust provides the mechanism for the crustal plates to float and move past one another. Even earlier, I highlighted two other discoveries showing how important water is in lubricating the motions of these crustal plates. Without such lubrication, the earthquakes experienced on Earth's surface would be much larger and more devastating.
More recently, an article in Science shows how water is transported even deeper into Earth's mantle. Even though the density of water pales compared to rock (which is why the oceans reside on Earth's surface), a large amount of water does work its way into Earth's interior. As one oceanic crustal plate subducts under another plate, the water absorbed in the plate floats to the top of the plate and forms a channel of watery material. This material both lubricates the two interacting plates and provides a pathway for water into the deep mantle.
At this time, the details of how water interacts with the deep Earth are still largely unknown. However, scientists' understanding of these processes continues to grow. Given how critical water is to life's biochemistry and to the functioning of plate tectonics on Earth's surface, I expect and predict that scientists will discover additional ways that water facilitates life-critical processes deep inside Earth.