Oxygen Isotopes Support Our Moon’s Violent Origin

The "Giant Impact" hypothesis has the Moon formed from an impact between early Earth and a Mars-sized body (NASA)
The “Giant Impact” hypothesis has the Moon formed from an impact between early Earth and a Mars-sized body (NASA)

While it may not be a true “smoking gun” (there have been four and a half billion years of cooling off, after all!) scientists in Germany have found further support for the currently accepted scenario of the origin of our Moon, based on chemical analysis of rocks brought back by Apollo astronauts. (And yes, we really went to the Moon.)

The Moon has played a very important role in the evolution of Earth as well as all life on Earth. Its gravitational tug powers the tides, for one, which create very important ecological niches along the coastlines of every land mass, and it also acts as an “anchor” for our planet, slowing its rate of rotation and stabilizing its axial tilt (although its formation may be partly responsible for the tilt in the first place, but that’s just fine because we got seasons as a result.)

But the Earth didn’t always have the Moon. Earth most likely formed without any moon, but during the early rock-’em-sock-’em days of the Solar System when there were still many objects flying about, our barely-cooled Earth happened to have a run-in with another protoplanet. Now referred to as Theia, this other world was about the size of Mars — that is, half the diameter of Earth — and, as the “Giant Impact” hypothesis goes the collision between it and our planet blew out a large amount of molten material from both worlds into orbit around Earth (and totally destroying Theia in the process.)

While a debris ring may have been present for a short time, eventually all that stuff merged to form one or possibly briefly two bodies that coalesced into a single spherical satellite. Add four-plus billion years of cratering, cooling, and gradual outward spiraling and you get the Moon we all know and love today. (If you don’t love the Moon, you can get out right now. 😉 )

Rock collecting during Apollo 12 (NASA photo)
Rock collecting during Apollo 12 (NASA photo)

While this scenario makes the most sense based on how the Earth-Moon system is observed to be today, the tricky part of confirming this hypothesis has come in the form of composition of materials in both worlds. If an object of Theia’s size were to have impacted Earth to create the Moon, at the angles thought to have occurred, the makeup of the Moon should be a bit of both. But exactly how much hasn’t yet been determined or agreed upon — models have ranged from the Moon being anywhere from 8% to 90% of the ill-fated Theia… not to mention any significant differences between Earth and the Moon remained unfound.

As it turns out though, new analysis of oxygen isotopes in Apollo rock samples, performed by a research team led by Daniel Herwartz from the University of Cologne in Germany, show the Moon may be an even 50/50 mix of both Earth and Theia. And while the preliminary results are far from glaring, they do help support the Giant Impact hypothesis… if just enough to put another point on its side.

“It is a relief that a [disparity in ratios] has been found, since the total absence of difference between Earth and moon would be hard to explain,” Caltech planetary scientist David Stevenson wrote to AAAS Science writer Daniel Clery.

Read more about these findings here and here.

One Comment

  1. Almost unbelievable, the whole saga. It was solved back in the APOLLO days. Wasn’t even aliens. Pity, because it’s such a perennial non-event, anything to break the monotony would be good.. You have two objects which can be partially sampled. Existing samples go close to proving common origin for sampled parts of both. One is a planet with a full fledged iron core: the other is a planet formed largely from the stony mantle of other planet(s). THEREFORE: Look for planet(s) missing stony mantle, in case they are a possible donor. Asteroids lack necessary volume: Mercury, lacking approx. 1/2 its mantle, (S.R. Taylor, 1999, referenced in my paper) had both potential volume and now has exceptional orbital inclination. . Earth possesses neither of these necessary features. Could Mercury or some lost planet(s) have been stripped to provide lunar material and also material which fell to Earth? This would explain the chemical similarity. (The moon of course could have been formed close to Mercury early on, and subsequently been captured by Earth.)

    The chemistry fits this hypothesis. The mechanics can fit this hypothesis. Everything fits this hypothesis. An infant can see as much. These German analytic results yet again certify this hypothesis, at least in principle. Enstatite Chondrites, eh? Guess where they are thought most likely to have originated? Either Mercury, or perhaps even closer to the centre. Sherlock Holmes you don’t need to be. Please consult Common Donor Capture Lunar Origin on GOOGLE, for the (painfully obvious) chemical confirmation of how the moon was provided for us.


Comments are closed.