New research has suggested that platinum and gold may have originally come from moon-sized bodies that are believed to have collided with Earth billions of years ago. Called planetesimals, these large bodies continually hit our planet until about 3.8 billion years ago, when such impacts became less frequent. During such events, matter was exchanged between them and the planet, while more was jettisoned into space.
This is a process generally known as accretion, and the period is called late accretion. According to some theories, this might help explain the formation of the moon, and why it and the Earth have such similar compositions.
Platinum and Gold and Their Extraterrestrial Origins
This newest research was supported by the Solar System Exploration Research Virtual Institute (SSERVI), a NASA organization. It was carried out by the Southwest Research Institute (SwRI) and the University of Maryland, both in the United States.
In a study paper released in the journal Nature Geoscience, Simone Marchi and his team explain that accretion may not have only affected the crust and mantle, as generally believed. Instead, the impacts of the Earth and planetesimals could have even exchanged matter from their cores. This theory is based on high-resolution impact simulations that the researchers conducted.
The researchers also believe that the amount of matter exchanged may have been 2 to 5 times higher than the 0.5 percent that is generally theorized. In particular, they noted that the amounts of iridium, platinum and gold (all of which tend to bond with metallic iron) in the mantle are higher than would be expected if they only resulted from core formation.
As such, they believe that this indicates late accretion after the core formation was already complete. All this means that accretion had more of an impact on the planet and its formation than previously believed.
Marchi said that: “These results have far-reaching implications for Moon- forming theories and beyond.”
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