The formation of the Earth-Moon system has long been theorized to have been heavily influenced by the impact of a Mars-sized celestial body, commonly called "Theia" by scientists. The Moon’s formation is theorized to have occurred when this object struck the primordial Earth, spinning off a portion of it’s mass, that formed into the Moon as we know it today. However, a common question has dogged the issue since it’s conception: did Theia just strike a glancing blow to the primordial Earth, or did it strike it head-on?

A new study out of UCLA may have answered that question: Using rock and soil samples taken by the Apollo 12, 15, and 17 missions, the researchers analyzed the ratios of oxygen and tungsten isotopes found in the samples, and found they were strikingly similar, meaning the Earth and Moon were formed from the same materials.

If Theia had only struck Earth with a glancing blow, then the Moon would be made up partially of materials from Theia, resulting in a different mix of isotopes. But a head-on strike would result in the mixing of the materials of Earth and Theia, resulting in the similarity of the materials being seen in the lunar samples.

"The collision was so vigorous, so powerful, so rich in energy that it probably mixed the whole system very thoroughly," remarks Edward Donald Young, the paper’s lead author a professor at UCLA’s Department of Earth, Planetary, and Space Sciences. 

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