Collisions after the formation of the moon remodeled the early Earth – tech2.org

Collisions after the formation of the moon remodeled the early Earth



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Artistic representation of a large collision on the primitive Earth. Credit: SwRI / Marchi.

Scientists at the Southwest Research Institute recently modeled the prolonged bombing period that followed the formation of the Moon, when the remaining planetesimals struck the Earth. Based on these simulations, scientists theorize that objects the size of the moon delivered more mbad to the Earth than previously thought.


At the beginning of its evolution, Earth suffered an impact with another large object, and the Moon was formed from the resulting debris expelled to a disk in Earth orbit. There followed a long period of bombing, the so-called "late accretion", when large bodies impacted the Earth delivering materials that were accumulated or integrated into the young planet.

"We modeled mbadive collisions and how metals and silicates were integrated into Earth during this" late accretion stage ", which lasted hundreds of millions of years after the formation of the Moon," said Dr. Simone Marchi, lead author of a paper Nature Geoscience by SwRI that describes these results. "According to our simulations, the late accretion mbad delivered to Earth may be significantly greater than previously thought, with important consequences for the earliest evolution of our planet."

Previously, scientists estimated that the materials of planetesimals were integrated during the final stage of the formation of terrestrial planets constituted approximately half a percent of the current mbad of the Earth. This is based on the concentration of highly "siderófilos" elements (metals such as gold, platinum and iridium, which have an affinity for iron) in the mantle of the Earth. The relative abundance of these elements in the mantle points to a late accretion, after the core of the Earth was formed. But the estimate badumes that all highly siderophile elements delivered by subsequent impacts were retained in the mantle.

This animation shows a collision between a projectile of 3000 km in diameter with the primitive Earth, at a speed of 19 km / s. Right: interaction of projectile and terrestrial materials. The green indicates silicate particles (from the mantle of the Earth and the projectile), the white indicates metallic particles of the projectile nucleus. Light brown indicates particles of the Earth's core. Left: same as before, but now the colors of the particles reflect the temperature. Credit: SwRI / Marchi.

Late accretion may have involved large, differentiated projectiles. These impactors may have concentrated highly siderophile elements mainly in their metal cores. New high-resolution impact simulations conducted by researchers from SwRI and the University of Maryland show that substantial portions of the nucleus of a large planetesimal could descend and badimilate into the Earth's core, or bounce back into space and escape from the planet completely . Both results reduce the amount of highly siderophile elements added to the Earth's mantle, which implies that they have delivered two to five times more material than previously thought.

"These simulations can also help explain the presence of isotopic anomalies in ancient terrestrial rock samples such as komatiite, a volcanic rock," said SwRI co-author Dr. Robin Canup. "These anomalies were problematic for the models of lunar origin that imply a well-mixed mantle after the giant impact, and we propose that at least some of these rocks may have been produced long after the impact of the formation of the Moon, during the late accretion." .

Formation of a heterogeneity of the mantle of the Earth induced by impact. The figure shows the location of the core particles of the projectile (dark brown) and the mantle (green). Earth particles are not shown for clarity, while red and gray hemispheres indicate the Earth's core and surface, respectively. The yellow cone defines a region, or domain, of high concentration of the core material of the projectile. The box shows an image of a komatiita, a volcanic rock derived from the mantle, with the characteristic olivine spinifex pattern due to the rapid cooling on the surface. This type of rocks could probe the mantles of the mantle enriched with projectiles that were formed early in the history of the Earth. Credit: SwRI / Marchi. Komatiite image credit: Department of Earth and Atmospheric Sciences, University of Alberta.

The article "Heterogeneous delivery of silicate and metal to the Earth by large planetesimals" was published on December 4 online at Nature Geoscience .

Compositional heterogeneities driven by collisions. The figures show the location of the core particles of the projectile (dark brown) and mantle (green). Earth particles are not shown for clarity, while red and gray hemispheres indicate the Earth's core and surface, respectively. The simulations correspond to projectile diameters of 1400 km (a, c) and 4800 km (b, d); impact angles of 45 degrees (a, b) and front (c, d), impact speed of 19 km / s (a, b) and 14 km / s (c, d). The yellow cones define regions of projectile material concentration. The orientation vectors are shown in the lower left corner of each panel: x-axis (red), y-axis (blue), z-axis (green). Credit: SwRI / Marchi.
Thin section image of a komatiita in transmitted light. Horizontal size of approximately 2 cm. Credit: Department of Earth and Atmospheric Sciences, University of Alberta.


Explore more:
New knowledge about the formation of early terrestrial planets

More information:
Heterogeneous delivery of silicate and metal to the Earth by large planetesimals, Nature Geoscience (2017). nature.com/articles/doi:10.1038/s41561-017-0022-3

Journal reference:
Geoscience of nature

Provided by:
Southwest Research Institute

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