When worlds collide: Earth is really two planets, study finds
The Earth is actually composed of two planets that fused together during a head-on collision 4.5 billion years ago, suggests a team of scientists in a study .
Scientists have largely accepted the "giant impact" hypothesis to explain the moon鈥檚 existence: about 4.5 billion years ago, a Mars-sized planet named Theia swiped the Earth at a 45-degree angle, throwing up a giant cloud of debris that would form the moon.聽
But after comparing oxygen isotopes from moon rocks and volcanic rocks from Hawaii and Arizona, these scientists believe Theia鈥檚 impact was a 鈥渉ead-on assault,鈥� not a mere sideswipe.聽聽
鈥淲e don鈥檛 see any difference between the Earth鈥檚 and the moon鈥檚 oxygen isotopes; ,鈥� said Edward Young, lead author of the study and a professor of geochemistry and cosmochemistry at the University of California, Los Angeles, in a statement. 聽聽
And Dr. Young says the isotopes鈥� similarity proves the scale of the impact Theia had on Earth.聽
鈥淗ad Earth and Theia collided in a glancing side blow, the vast majority of the moon would have been made mainly of Theia, and the Earth and moon should have different oxygen isotopes,鈥� the press release explains. 鈥淎 head-on collision, however, likely would have resulted in similar chemical composition of both Earth and the moon.鈥澛�
Because the collision was so forceful, 鈥淭heia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,鈥� explained Young.聽
Oxygen, when bonded to silica and other elements, makes up 90 percent of rocks鈥� volume and 50 percent of their weight, so scientists can use rocks鈥� oxygen atoms to differentiate between different planetary bodies in our solar system.
Like a chemical 鈥渇ingerprint,鈥� planets in Earth鈥檚 solar system have unique ratios of 17 翱听补苍诲 16 O, two distinct oxygen isotopes.聽
But because the Earth and moon鈥檚 fingerprints are 鈥渋ndistinguishable,鈥� they must both had a fair share of Theia, says Young.聽
Young and his colleagues are not the first to suggest a head-on collision occurred.
In 2012, Matija Cuk and Sarah Stewart, scientists from the SETI Institute and UC Davis respectively, published a study in Science that supports the same hypothesis.聽
鈥淚t seems unlikely that Theia would be nearly isotopically identical with Earth, so if Theia were a greater contributor to the moon, from Earth,鈥� Space.com explained in 2012. 聽聽聽
Young says each subsequent comparison between rocks further proves Theia鈥檚 equal integration into both the moon and Earth.
鈥淎s we continue to improve our ability to make measurements, the moon and Earth continue to be more and more alike isotopically,鈥� Young told Space.com.
