Precious metals on earth come from meteorites

:) hello steemians! Some of the noble and rare metals in the world including platinum and iridium can show their presence in the Earth's crust and in iron meteorites and iron-iron meteorites that are chunks of large amounts of asteroids that have undergone a geological process early in the solar system.

Dr. Gerhard Schmidt from the University of Mainz, Germany, calculated about 160 metal asteroids that have a diameter of 20 km, which is estimated to have concentrations of these rare metals. The rare metals found in the Earth's crust are known as Highly Siderophile Elements (HSE). The Siderophile element is a group of transition metals that have a very high density bound to iron metal in solid or liquid conditions. The HSE group consists of rhenium (Re), Osmium Os), iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt), palladium (Pd) and gold (Au).

According to Dr. Schmidt's key to understanding the origin of the planet is the knowledge of the abundance of HSE in the crust and mantle of Earth, Mars and the Moon. Dr. Schmidt found a uniform abundance of HSE in the top layer sample of the Earth's crust. After performing a comparison with the number of HSEs in the meteorite, it appears that this HSE has a cosmic chemical source.

In 12 years, Dr. Schmidt analyzed the concentrations of HSE on meteorite crash sites around the world, as well as on examples of Earth's crust and mantle. In addition, he also compared the data he got on Earth with Breccias collision data on the Moon brought by Apollo missions. The comparison is also done with meteorites from Mars, which is believed to be an example of Mars's crust and mantle.

HSE itself is located in the nebula that is the origin of Earth's formation. But as this young planet undergoes evolution, the existing HSE undergoes heating and then disappears with other heavy elements from the silicate mantle to the core of iron and nickel-rich metal. The existence of HSE in the mantle is still a debate and the widely accepted theory is that HSE is added by meteorite collisions as a layer of matter on the Earth's surface after the formation of nuclei about 20-30 million years ago after planetary accretion. It is estimated that the collision occurred from Mars-sized objects that trigger the formation of the Moon.

^{Artist's depiction of a collision between two planetary bodies. Such an impact between Earth and a Mars-sized object likely formed the Moon.,wikipedia}

Different meteorite classes have a characteristic comparison of HSE elements that give an indication of where they are formed in the Solar System. And the HSE comparison characteristics in Earth's upper mantle (eg ruthenium/iridium element having ratio 2) matches the theoretical prediction of asteroid formation in the Mercury-Venus area.

Earth is a different object with a nickel-iron core, silicate mantle, and an evolved silicate crust. In this study, the HSE abundance ratios in the Earth's crust are much higher than those found in rock meteorites, known as chondrites. These chondrites represent the earliest materials that form the Solar System. The HSE ratios were found to be similar to those in the iron-iron meteorite. The meteorite is a large piece of an asteroid that has undergone internal heating in the past to form a liquid metal core. HSE is typically concentrated in the liquid core and at the boundary with solid matter, ie, in rock sheath. However, the true ratio of different metals depends on the physical conditions in which they are formed.

The HSE ratios found in Earth's top mantle are not entirely the same as meteorite specimens found worldwide. The only resemblance is the ratio of HSE to the Charlotte metal meteorite.

To date, there are about 20 meteorites of iron and 20 rock meteorites, called chondrites that have been identified from 175 due to collisions on earth, while 135 others remain unknown. And among these, no meteorites have been identified in the Mercury-Venus area.

Some meteorites from Mars that are thought to represent Mars's crust also have HSE values that are almost similar to the meteorite group of iron and rock meter. Thus it is estimated that the same process also occurs on Mars. Thanks!

BEST REGARDS @irza

Reference :

https://space-facts.com/meteorites/
https://www.smithsonianmag.com/science-nature/what-is-rarer-than-gold-45073180/
https://www.sciencedirect.com/science/article/pii/S0012821X99002800
https://geology.com/meteorites/iron-meteorites.shtml
https://www.sciencedaily.com/releases/2008/09/080922100455.htm
https://pubs.geoscienceworld.org/msa/rimg/article/81/1/161/141067/highly-siderophile-elements-in-earth-mars-the-moon
https://www.space.com/17777-what-is-earth-made-of.html
https://www.space.com/19275-moon-formation.html
https://www.space.com/26142-moon-formation-giant-impact-theory-support.html