Study Locates Remnants of Prehistoric Moon-Forming Planet that Struck Earth

Nov 14, 2023

Birth of the Moon

Scientists widely believe the moon was created from a collision between Earth and a second planet they call Theia. They just haven’t proved it.

But a new study may push that theory closer to fact. The study was published in the journal Nature. It explored the nature of large blobs under the African and Pacific tectonic plates. They could be remnants of a planet that crashed into ours 4.5 billion years ago, the study found.

Researchers conceived this “giant impact theory” decades ago. The theory holds that after Earth was fully formed, a planet roughly the size of Mars struck it, kicking up a debris field that formed our moon over time. Scientists named this theorized planet “Theia.” Why? It's the name of the titan in Greek myths who mothered the moon goddess Selene.

Evidence of the destroyed planet’s existence has been hard to find. No remnants have been unearthed anywhere in the solar system. The new study suggests the search was focused in the wrong places.

“Where’s (Theia)? ... it’s in the Earth.” Qian Yuan, the study’s lead author and a professor, stated this to Agence France-Presse. Yuan said he thought of this during a lecture on the Theia theory.

Yuan focused on the two blobs which were unearthed in the 1980s. They've puzzled scientists since then. And the swaths, which are big as continents and rest about 1,800 miles below the planet’s surface, are much more dense and hotter than the nearby layers of rock. Yuan’s team made a computer model showing how a planet crashing into Earth could bury some of its remains at that depth under the surface.

In an CNN interview, Yuan stressed that “this is an idea; this is a hypothesis.” But other scientists are taking it seriously.

Reflect: Why is it important to have theories and hypotheses in science in order to explain the world around us and its history?

Based on the information in the infographic, which event happened first? (Common Core RI.5.7; RI.6.7)
a. debris was propelled into space
b. debris cooled down
c. fragments clumped in orbit
d. Theia collided with Earth
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