LF: Earth is actually two planets, scientists conclude

The early Earth was mixed with a baby planet called Theia following a head on collision 4.5 billion years ago, scientists have found

It means that the collision between Their and the early Earth was so violent that the two planets effectively melded together to form a new planet, a chunk of which was knocked off to form the Moon.

“We don’t see any difference between the Earth’s and the Moon’s oxygen isotopes; they’re indistinguishable,” said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.

“Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them.

“This explains why we don’t see a different signature of Theia in the Moon versus the Earth.”

The crash with Theia happened approximately 100 million years after the Earth formed, almost 4.5 billion years ago.

It was thought Theia had collided with Earth at an angle of 45 degrees or more, described by the report authors as a ‘powerful side-swipe’

The researchers analysed seven rocks brought to the Earth from the Moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle -- five from Hawaii and one from Arizona.

The key to reconstructing the giant impact was a chemical signature revealed in the rocks’ oxygen atoms. More than 99.9 percent of Earth’s oxygen is O-16, so called because each atom contains eight protons and eight neutrons.

But there also are small quantities of heavier oxygen isotopes: O-17, which have one extra neutron, and O-18, which have two extra neutrons.

In 2014, a team of German scientists reported in Science that the Moon also has its own unique ratio of oxygen isotopes, different from Earth’s. The new research finds that is not the case.

Prof Young’s research team used state-of-the-art technology and techniques to make extraordinarily precise and careful measurements, and verified them with UCLA’s new mass spectrometer.

Theia, which did not survive the collision - except that it now makes up large parts of Earth and the Moon - was growing and probably would have become a planet if the crash had not occurred, added Prof Young.

Prof Young and some other scientists believe the planet was approximately the same size as the Earth; although believe it was smaller, perhaps more similar in size to Mars.

A head-on collision was initially proposed in 2012 by Matija Cuk, now a research scientist with the SETI Institute, and Sarah Stewart, now a professor at UC Davis; and, separately during the same year by Robin Canup of the Southwest Research Institute.

The new research was published in the journal Science.

William K. Hartmann painted this rendering of the first moments of impact

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This scenario does explain why the moon is so perfectly tidally locked to the earth (same side of moon always facing the earth). If the moon was formed by rubble from the collision while orbiting earth then that's what you get.

If the moon was formed from debris then in order to assume a spherical shape it must have continued to spin for a long time but Earth's gravity would have slowed it down and locked it. It was also once closer than it is so tidal forces on Earth must have created some interesting effects