Researchers now say that it was "like a sledgehammer hitting a watermelon."
For decades now, scientists have had debate after debate about what is would have looked like when the Moon broke off from Earth and formed 4.5 billion years ago. No one expected it to be a violent activity, but that is exactly what new chemical evidence shows.
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In fact, researchers now say that it was "like a sledgehammer hitting a watermelon."
Up until now, the theory that was widely accepted said that the Moon was formed after a Mars-size object collided with the then developing Earth, about 20 to 100 million years after the Solar System formed.
Earth really wasn't changed by the collision, but the object that hit us was. Its mantle sank into and merged with our core and mantle. Everything left over was ejected into our orbit and a disk was formed. From that disk, the Moon took shape.
The thought was that everything was fairly simple and pretty non-violent - in fact, other theories and pieces of evidence seemed to support the idea. Still, there has always been a problem with the hypothesis. The problem was that chemical analysis on samples brought from the Moon back to Earth were nearly identical.
Simulations showed that most of the material that made up the Moon would have had to come from the body that hit Earth, rather than Earth itself. However, it is unlikely that the two would have to same chemical make-up.
Geochemists from Harvard and Washington University found that the hypothesis couldn't be more wrong.
"We’re still remeasuring the old Apollo samples from the '70s, because the tech has been developing in recent years," one of the team, Kun Wang from Washington University, told Ria Misra from Gizmodo. "We can measure much smaller differences between Earth and the Moon, so we found a lot of things we didn’t find in the 1970s. The old models just could not explain the new observations."
In fact, there is evidence that the materials could not have come from anywhere other than Earth.
As Loren Grush explains over at The Verge: "The collision that formed the Moon wasn’t low energy at all, [Wang] argues. Instead, the impact was extremely violent, pulverising most of Earth and the impactor, and turning them into a vapour. In this scenario, the vaporised Earth and impactor mix together into a giant dense atmosphere. This atmosphere then cools and condenses into our planet and its satellite."
Of course, this is a bold claim, but it could be true. It would certainly change a lot about how we view the creation of the Moon.
"I’m very pleased overall with what they have done, I just wish they had used better samples," Munir Humayun, a geologist at Florida State University who was not involved in the study, told The Verge, adding that they don't have the data to support the hypothesis just yet.
"It took people decades to accept this giant-impact hypothesis," he says. "Now we’re saying that [the] giant impact hypothesis is not right, so it may take 10 to 20 years to accept the new model."