spaceSpace and Physics

Earth’s Water May Have Arrived Earlier Than We Thought


Jonathan O'Callaghan

Senior Staff Writer

When did Earth's water arrive? NASA

Here’s a fun fact for you: Although Earth’s oceans cover 71 percent of the surface, just 0.023 percent of our planet’s mass is water. But where did that water come from?

That’s a question that’s long been pondered, but a new study aims to answer it in part by suggesting Earth got its water pretty early on.


In a paper published in the journal Geochemica and Cosmochimica Acts, scientists studied rare basaltic meteorites called angrites. From this, they were able to suggest our water started arriving before or very soon after our planet was fully formed 4.54 billion years ago.

Of course, back then our planet was far too hot for liquid water to exist. But when it did start cooling down, the researchers suggest our water was ready and waiting.

“It’s a fairly simple assumption to say that Earth’s water at least started accreting to Earth extremely early, before the planet was even fully formed,” lead author Adam Sarafian from the Massachusetts Institute of Technology told Astrobiology Magazine.

“This means that when the planet cooled enough so that liquid water could be stable at the surface, there was already water here.”


The team’s paper deals with meteorites called angrites, which are thought to have formed about 4.56 billion years ago. They measured the amount of a mineral called olivine in these basaltic meteorites, which indicates their volatile content – things with low boiling points like water. And it seems like they may have delivered at least some of our water here.

They go on to discuss a possible origin for Angrite meteorites, which hasn’t been done yet. They suggest an angrite parent body (APB) more than 540 kilometers (335 miles) across, or perhaps more than 680 kilometers (420 miles) may be the culprit.

That lower estimate is very similar in size to the modern large asteroid Vesta in the asteroid belt, 525 kilometers (326 miles) across. However, it’s likely the APB no longer exists.

“Despite its proposed substantial size, the APB [Angrite Parent Body] has not been physically observed, although there are smaller asteroids that exhibit spectral features that are very similar to the angrites,” the team writes in their paper. “Consequently, the APB was likely disrupted or destroyed.”


The study gives us an interesting new look, though, at the origin of Earth’s water. There are still plenty of unanswered questions, but perhaps we’ve had it for longer than we thought.

(H/T: Astrobiology Magazine)


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