2023-11-01 19:00:25
A scientific team from China, the United States and the United Kingdom has recently discovered that a large anomaly inside the Earth It may be a remnant of the collision, which occurred about 4.5 billion years ago, that formed the Moon.
According to the authors of the study published in Naturethe research offers important new data not only on the internal structure of the Earth, but also on its long-term evolution and the inner formation of the solar system.
The study is based on computational fluid dynamics methods, pioneered by Professor Deng Hongpingfrom the Shanghai Astronomical Observatory, Chinese Academy of Sciences.
The formation of the Moon has been a constant enigma for several generations of scientists. Prevailing theory suggests that during the late stages of Earth’s growth, about 4.5 billion years ago, a massive collision – known as the ‘big impact’ – occurred between the early Earth (Gaia) and a protoplanet the size of Mars called Theia. It is believed that our satellite was formed from the debris generated by this collision.
About 4.5 billion years ago, a massive collision occurred between the early Earth (Gaia) and the protoplanet Theia. It is believed that the Moon was formed from the debris generated by this collision
Las numerical simulations indicate that the Moon probably inherited material primarily from Theia, while Gaia, due to its much greater mass, was only slightly contaminated by material from Theia.
Since Gaia and Theia were relatively independent formations and were composed of different materials, theory suggested that the Moon – dominated by Theia material – and our planet – in which Gaia material predominated – must have different compositions.
Remarkably similar compositions
However, high-precision isotopic measurements later revealed that the compositions of the Earth and Moon are remarkably similar, calling into question the conventional theoryl of the formation of our satellite.
To further investigate the theory of lunar formation, Deng began researching the formation of the Moon in 2017. He focused on developing a new computational fluid dynamics method called Meshless Finite Mass (MFM), which excels at precise modeling of turbulence and mixing of materials.
Using this approach and with numerous simulations of the large impact, Deng discovered that the early Earth exhibited mantle stratification after the collision, and that the upper and lower mantles had different compositions and states.
High-precision isotopic measurements revealed the compositions of the Earth and Moon are remarkably similar, calling into question the conventional theory of lunar formation
Specific, the upper mantle had a magma oceancreated by exhaustive mixing of material from Gaia and Theia, while the lower mantle remained largely solid and retained the material composition of Gaia.
“Previous research had placed excessive emphasis on the structure of the debris disk – the precursor of the Moon – and had overlooked the impact of the great collision on the early Earth,” explains Deng.
After discussing with geophysicists from the Federal Polytechnic School of Zurich (Switzerland), the Chinese researcher and his collaborators realized that this stratification of the mantle could have persisted to the present day, which corresponds to the global seismic reflectors of the middle mantle ( located about 1,000 km below the Earth’s surface).
Examples of mantle heterogeneity
In particular, the entire lower mantle of the Earth may still be dominated by pre-impact Gaian material, which has a different elemental composition (including a higher silicon content) than the upper mantle, according to Deng’s earlier study.
“Our discoveries call into question the traditional idea that the great collision led to the homogenization of the early Earth,” says the scientist. “Instead, that giant impact that formed the Moon seems to be the origin of the heterogeneity of the primitive mantle and marks the starting point of the geological evolution of the Earth over the course of 4.5 billion years,” he highlights.
Another example of the heterogeneity of the Earth’s mantle are two anomalous regions called Large Low Velocity Provinces (LLVPs) that extend for thousands of kilometers at the base of the mantle. One is located under the African tectonic plate and the other under the Pacific tectonic plate. When the seismic waves pass through these areas, the speed of the waves is considerably reduced.
LLVPs have important implications for the evolution of the mantle, the separation and aggregation of supercontinents and the structures of the Earth’s tectonic plates. However, its origins remain a mystery.
Yuan Qian, from the California Institute of Technology, along with other collaborators, proposed that LLVPs could have evolved from a small amount of Theian material that entered Gaia’s lower mantle. Later, they invited Professor Deng to explore the distribution and state of Teian material deep in the Earth after the giant impact.
With in-depth analysis and more precise simulations, the team discovered that a significant amount of material from the Theian mantle, about 2% of Earth’s mass, entered Gaia’s lower mantle.
By analyzing in-depth previous simulations of the big collision and performing new, more accurate simulations, the team found that a significant amount of material from the Theian mantle, about 2% of Earth’s mass, entered the mantle. inferior of Gaia.
Next, Deng invited the computational astrophysicist Jacob Kegerreis to confirm this conclusion using traditional smoothed particle hydrodynamics (SPH) methods.
Rastros del manto protoplaneta Theia
The research team also calculated that this Teian mantle material, similar to lunar rocks, is enriched in iron, making it denser than the surrounding Gaian material. As a result, it rapidly sank to the bottom of the mantle and, in the course of long-term mantle convection, formed two prominent LLVP regions, which have remained stable throughout 4.5 billion years of geological evolution.
Small amounts of deep heterogeneity may be brought to the surface by mantle plumes like those that probably formed Hawaii and Iceland.
Deep mantle heterogeneity, whether in mid-mantle reflectors or basal LLVPs, suggests that the Earth’s interior is far from a uniform system.
In fact, small amounts of deep heterogeneity can be brought to the surface by mantle plumes—cylindrical upward thermal currents caused by mantle convection—like those that likely formed Hawaii and Iceland.
For example, geochemists studying the isotopic ratios of rare gases in samples of Icelandic basalt have found that these samples contain different components from typical surface materials.
These components are remnants of heterogeneity in the deep mantle that date back more than 4.5 billion years and serve as keys to understanding the initial state of the Earth and even the formation of nearby planets.
This research even serves as inspiration to understand the formation and habitability of exoplanets beyond our solar system.
Deng Hongping (Shanghai Astronomical Observatory)
According to Yuan, “by precise analysis of a broader range of rock samples, combined with more refined models of giant collisions and models of Earth evolution, we can infer the material composition and orbital dynamics of the primordial Earth – Gaia – and Theia. “This allows us to constrain the entire history of the formation of the inner solar system.”
For his part, Deng sees an even broader role for the current study. He believes that this research “even serves as inspiration to understand the formation and habitability of exoplanets beyond our planet.” solar system”.
Reference:
Qian Yuan et al. “Moon-forming impactor as a source of Earth’s basal mantle anomalies”. Nature (2023)
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