A Watery Beginning

It’s a substance that covers around 71% of Earth’s surface and one that is needed, to varying degrees, by nearly all living organisms. Despite its importance and prevalence, science is still trying to nail down the specifics of how, when, and from where Earth’s water originated. Recently, French scientists have determined that a type of meteorite, similar in composition to the building blocks of early Earth, contains enough water to strongly suggest that most of Earth’s water didn’t come from comets or asteroids, but was present from the very earliest stages of its formation.

The type of meteorite that the French team studied is called an enstatite chondrite. They are a rare kind of meteorite on present-day Earth, making up only 2 percent of all the meteorites collected. However, they present a very special snapshot into the chemical makeup of early Earth because they are thought to be very similar to the composition of the material which accreted, or came together, to form Earth. By examining the isotopes of hydrogen, oxygen, titanium, and calcium in these meteorites, they showed a similar chemical fingerprint to those same elements in Earth’s mantle today.

More importantly, the amount of hydrogen and oxygen locked up in the minerals of these meteorites, according to the research team, would have been sufficient to deliver more than three times the amount of water contained in Earth’s oceans, at present. This latest finding largely contradicts the previous assumption that enstatite chondrites, and thus Earth’s building blocks, were largely devoid of water and that Earth’s water had come from comets or asteroids from the far reaches of the solar system.