About 71% of Earth’s surface is covered in water. That’s 326 million trillion gallons of water, an almost unfathomable amount. Beneath Earth’s crust, contained in its mantle and core, enough water molecules are floating around to create a second set of oceans, and then some. These subterranean water molecules aren’t all the same. Their differences provide vital clues to the early solar system and how Earth and all of its water came to be.
A Chemistry Lesson
Water is made up of two hydrogen atoms and a single oxygen atom. Hydrogen is the most abundant element in the universe, but not every atom of hydrogen is the same. The most common form of hydrogen, protium, is made up of a single electron orbiting a central proton. Of the two other types, or isotopes, of hydrogen, only one is stable. Deuterium is a heavier version of protium, containing a proton and a neutron at its center.
Deuterium and protium are both able to bond with two oxygen atoms to form water molecules. Most water is made up of oxygen and protium, as deuterium is far less common. The water you interact with on a daily basis is only about 0.0156% “heavy water.” It tastes no different than regular water, and you could safely consume about a gallon and a half of pure deuterium water before you noticed any side effects.
Water In The Solar System
Scientists can gather clues about our planet’s origins by studying isotopes and their ratios relative to those found elsewhere in our cosmic neighborhood. Asteroids, for example, we know contain similar proportions of “normal water” to heavy water as our oceans do. Earth was formed by the fusion of asteroids and other rocky matter in the early solar system. The similar ratios of protium to deuterium support this theory.
Molecular water samples from the planet’s interior contain significantly less deuterium, suggesting a different origin. In addition to bits of rock, planetary nebulae are comprised of copious amounts of dust and gas. The leading theory explaining the difference in deuterium concentrations points to dust from the nebula.
Putting It All Together
The discovery of different concentrations of heavy water has not only given scientists insight into how our planet was formed, but it may help them better understand how other planets are created. More importantly, the discovery of significant amounts of water beneath Earth’s crust could mean that water exists on other planets. In Earth’s mantle, there is enough water from the solar nebula to form two whole oceans. In the core, there could be enough to create four or five.
Molecules of protium-water drawn in from the planetary nebula and locked away in the planet’s interior hold the exciting promise that exoplanets formed under similar conditions could also contain water in their interiors. We also now know with greater certainty that planets aren’t entirely created by the fusion of rocky bodies within planetary nebulae, but that they draw in dust from the surrounding medium, and that makes up a significant portion of its interior.