Making Mountains Move

Geophysicists have known for years that the energy moving Earth’s crust pieces toward and away from one another (plate tectonics) comes from the flow of heat from the core up toward the surface. Recently, however, planetary physicist David Stevenson, of the California Institute of Technology, has shown that plate tectonics, oddly enough an essential for life (though earthquakes may be hard for most people to appreciate), need more than just an energy source. They need a lubricant.1 This added complication to a life-essential physical process represents added support for divine “engineering” of Earth for life.

Earth’s lubricant is its huge quantity of surface water. As ocean plates sink into the mantle (ocean plates are denser than continental plates), they carry water into the mantle and, in doing so, lower the melting point of that mantle. The result is increased volcanic activity and a softening of the mantle layers on which tectonic plates slide. In other words, Earth’s just-right-for-life level of volcanic and plate tectonic activity depends crucially on its enormous—and notably rare—quantity of liquid surface water.2

The connection between life’s survival and volcanic and plate tectonic activity is this: such activity distributes life-essential nutrients relatively evenly across Earth’s surface. Erosion alone would concentrate nutrients in Earth’s basins and deplete them everywhere else.

Support for Stevenson’s analysis comes from studies of the planet Venus. Venus has internal heat sources comparable to Earth’s. Yet Venus lacks any observable plate movement. Apparently, the lack of a lubricant accounts for the lack of tectonic activity. The conclusion: Fine-tuning the energy source behind a planet’s plate tectonics and vulcanism is not enough to guarantee life-sustaining conditions. One must also fine-tune the quantity and the quality of the tectonic lubricant.