Earth is two fused planets, new research suggests

How many planets are you sitting on right now? If you answered one, you’re absolutely correct. If you answered two, you’re wrong, but maybe not quite as wrong as it might have seemed at first.

For a number of years, there’s been a theory doing the rounds that Earth collided head on with Theia 4.5bn years ago. What’s Theia, and why haven’t you heard of it? Well, Theia is a planet that didn’t come off so well from the collision, hence why you don’t see it on astronomy charts nowadays. The theory suggests that the two planets collided, and part of Theia went on to form the moon. Imagine something like the video below, if you overlook the typo on Theia:

Others believe that Theia merely side-swiped the Earth, producing the moon on its way past. However, that doesn’t seem possible now, thanks to impressive new research from UCLA, which found a stunning similarity between the “fingerprints” of seven lunar rocks from the Apollo mission, and six volcanic rocks collected from the Earth’s mantle. The fingerprint in question is established by examining the oxygen isotopes contained within the rocks – counting the number of protons and neutrons, in other words.

Almost all of the oxygen on Earth is O-16 (eight protons, eight neutrons), but there’s a tiny proportion that’s O-17 and O-18. Less than 0.1%, in fact, but that ratio helps scientists identify where rocks come from. And they discovered that the moon rocks were identical to those found on Earth. That’s huge because, if the “Theia side-swipe” theorists were correct, you’d expect the moon rocks to be Theia ones.edward_young_and_colleagues_photo_credit_christelle_snow

“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” explained lead researcher Edward Young. “This explains why we don’t see a different signature of Theia in the moon versus Earth.”

This raises an interesting question about where Earth’s water comes from. A direct collision with another planet would probably strip any water from Earth, leaving scientists to ponder whether it only came back to the planet thanks to small asteroids colliding with us millions of years down the road.

Young believes Theia was roughly the same size as Earth, while other scientists speculate it was probably closer to Mars in scale. Either way, he believes that, had it survived the crash, Theia would have become a planet in its own right, rather than fusing with us.

If the research is correct, who knows where we’d be as a species without this massive event 4.5bn years ago?

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Images: UCLA and Maxwell Hamilton used under Creative Commons

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