Southern California, home to RTB, requires a huge quantity of water to maintain its large population and diverse economic and industrial activity. The region’s water needs exceed the local supply so an aqueduct system pipes water from various reservoirs throughout the state into the area. Removing access to these reservoirs would not only drop the population by a factor of a thousand or more (say, from 25 million to less than 25 thousand) but would also force the region to a near Stone-Age existence.
On a grander scale, Earth’s habitability relies on a vast underground reservoir for oxygen that relies on plates as aqueducts. Tectonic activity on Earth drives the plates that compose its surface deep underground. The plates carry along Earth’s mantle material containing oxygen bound to iron in a compound called iron oxide (also known as rust). As the plates descend deeper into the mantle, two important processes occur. First, the mantle material melts the iron oxide and causes the oxygen to become more reactive. Second, the higher temperatures and pressures result in the formation of a mineral known as majorite. The increased reactivity of the oxygen causes it to combine with the majorite.
A team of German geophysicists demonstrated in the laboratory that majorite forms under conditions present in the upper mantle.1 Furthermore, the team’s research showed that the capacity of majorite to “absorb” oxygen increases with pressure. Thus, majorite stores more oxygen as it moves deeper into Earth’s interior.
Eventually, the convection processes that cycle material through Earth’s interior bring the majorite back near Earth’s surface, where it releases its oxygen. The oxygen then becomes available for numerous oxidation reactions essential for life on Earth. In one critical reaction, the oxygen combines with hydrogen (which Earth continually exudes) to replenish the water in Earth’s oceans and atmosphere.
A sophisticated aqueduct system transports water from reservoirs to service Southern California’s water needs. Similarly, the tectonic activity within Earth provides the mechanism to transport oxygen to and from this majorite “storage tank.” Consequently, only planets of the right size and composition can utilize such an oxygen reservoir. The planet must contain the components of majorite in sufficient quantities. Additionally, only planets above a minimum mass will exhibit tectonic activity that interacts with the regions where majorite can form. For smaller planets, the pressures required to form majorite occur too deep in their interiors.
California’s reservoir and aqueduct system was designed to ensure that all its inhabitants receive adequate water regardless of the inevitable fluctuations in yearly precipitation. However, the system shows signs of aging and may inadequately fulfill its function in the near future. In contrast, the majorite reservoir and tectonic “aqueduct” at work inside Earth continues to perform flawlessly, as evidenced by the abundant liquid water on Earth’s surface for nearly four billion years. That is evidence of good design!
- Arno Rohrbach et al., “Metal Saturation in the Upper Mantle,” Nature 449 (September 27, 2007): 456–58.