In 1972, an American paleontologist and geographer proposed the Hadean Eon hypothesis. Before 4.6 billion years ago, Earth had still been a scorching ball of magma. Then a planet roughly the size of Mars collided with Earth. A considerable portion of the matter had been vaporized by the impact, forming an atmosphere composed of rock vapor. Part of it had melted completely into Earth, while another part had split away and formed the present-day Moon.
The scholar named that planet Theia, after the mother of the goddess Selene in ancient Greek mythology. The planet was said to have formed at one of the Lagrange points, then, as the gravitational pull of developing planets such as Venus increased, it left the Lagrange point and entered an orbit that collided with Earth.
To verify this hypothesis, America launched many scientific instruments to the Moon. But the period proposed by the Hadean Eon hypothesis happened to coincide with the final stage of the Apollo Program. Still, Apollo 15 discovered a crystal in the Apennine Mountains on the Moon that was 4.5 billion years old, known as the "Genesis Rock." Since Earth's surface had been entirely magma during the Hadean Eon, crystals and stones—solid rocks—could only form after it cooled. This "Genesis Rock" brought back from the Moon had formed a hundred million years earlier than the oldest zircon yet discovered on Earth. If it was real, Earth's age would have to be pushed back another hundred million years.
No matter how flawless a theory appeared on paper, it needed verification. If the Hadean Eon hypothesis was indeed true, then half of Earth's matter came from The Sun, and the other half came from the Moon.
It was a very romantic notion, but if Theia had indeed formed at a Lagrange point, then it