SPACE — An interdisciplinary international research team recently discovered a large anomaly deep in the Earth’s interior. Allegedly, this was caused by the remains of an object that hit the earth about 4.5 billion years ago, and formed the moon.
The research offers important new insights. It concerns not only the internal structure of the earth, but also the long-term evolution and formation of the inner solar system.
The research relies on computational fluid dynamics methods pioneered by Prof. Deng Hongping from the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences. The paper was published as the main cover in the journal Nature today, Thursday, November 2, 2023.
The formation of the moon has remained a puzzle for generations of scientists. The current theory states that in the final stages of Earth’s growth around 4.5 billion years ago, a large collision called the “giant impact” occurred between the ancient Earth (Gaia) and a Mars-sized protoplanet called Theia. Our moon is believed to have formed from debris resulting from this collision.
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Numerical simulations show the moon likely inherited the majority of its material from Theia. Meanwhile, Gaia, due to its much greater mass, is only slightly contaminated by Theian matter.
Because Gaia and Theia are relatively independent formations and consist of different materials, the theory states; the moon is dominated by Theian material and the Earth is dominated by Gaian material.
This means that the earth and moon must have different compositions.
However, high-precision isotope measurements later revealed that the composition of the Earth and the moon are very similar. This fact challenges conventional theories about the formation of the moon. Although various improved giant impact models are proposed, they all still face their own challenges.
To further refine the theory of lunar formation, Prof. Deng began researching lunar formation in 2017. He focused on developing a new computational fluid dynamics method called Meshless Finite Mass (MFM). This method is claimed to be superior in modeling turbulence and material mixing accurately.
By carrying out many simulations of giant impacts, Prof Deng found the young Earth showed mantle stratification after the impact. The upper and lower coats have different compositions and states. But in particular, the upper mantle displays a magma ocean from the mixing of Gaia and Theia material. Meanwhile, the lower mantle remains mostly solid and maintains the material composition of Gaia.
“Previous studies have placed excessive emphasis on the structure of the debris disk (the Moon’s predecessor) and ignored the impact of giant impacts on the early Earth,” Deng said.
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After discussions with geophysicists from the Swiss Federal Institute of Technology in Zurich, Prof Deng and collaborators realized that mantle stratification may still persist today. This corresponds to a global seismic reflector in the middle of the mantle, located about 1,000 km below the Earth’s surface.
According to Prof. Deng’s research, the entire lower Earth’s mantle is thought to still be dominated by pre-impact Gaian material. They have different elemental compositions, including higher silicon content than the upper mantle.
2023-11-02 11:50:00
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