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Elemental Indications of Impact Sites

Last Updated: 15th Jan 2019

By Dave Crosby

When Earth began 4.5 billion years ago, it was so hot it became a "differentiated planet" meaning the heaviest elements sank in weight order to the center and a crust was formed consisting of the lightest elements with only very small amounts of the heavier elements left above.

Earth layers

Over billions of years of weathering as the continents collided and bobbed up and down sediments accumulated varying from sandstone to limestone to shale to salt beds to mud and back again, with gravity constantly pulling the heavier elements down.

layer #1. the Crust
The continental layers consist predominantly of the 16 most common elements left in the earth’s crust - in descending percent amounts they are:

Oxygen 46.7%, silicon 27.7%, aluminum 8.1%, iron 5.1%, calcium 3.7%, sodium 2.8%, potassium 2.6%, magnesium 2.1%, titanium 0.62%, hydrogen 0.14%, phosphorus 0.13%, manganese 0.9%, fluorine 0.29%, barium 0.05%, carbon 0.094%, and strontium 0.037%.

Those 16 elements make up 99.9% of all mud. Anything beyond them is highly unusual.

A complete list of elements in the crust is here:
https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust
Abundance of Elements in Earth's Crust


From the beginning the earth's surface has been bombarded from outer space by asteroids, comets, and meteors of varying compositions,
creating many unique and valuable mineral locations.

www.popsci.com/60-tons-cosmic-dust-fall-earth-every-day
Until now, scientists didn't know how much of this cosmic dust was gathering on Earth (though they know rather a lot about how much is up in space). Researchers guessed that anywhere between 0.4 and 110 tons of the star stuff entered our atmosphere every day--that's a pretty wide range. But a recent paper took a closer look at the levels of sodium and iron in the atmosphere using Doppler Lidar, an instrument that can measure changes in the composition of the atmosphere. Because the amount of sodium in the atmosphere is proportional to the amount of cosmic dust in the atmosphere, the researchers figured out that the actual amount of dust falling to the earth is along the lines of 60 tons per day.


60 X 365 days = 21,900 tons /year X 1 million years = 21,900,000, tons = a lot of new soil!

Layer #2. the mantle (seldom receiving impacts)
www.universetoday.com/40229/what-is-the-earths-mantle-made-of/

In terms of its constituent elements, the mantle is made up of 44.8% oxygen, 21.5% silicon, and 22.8% magnesium. There’s also iron, aluminum, calcium, sodium, and potassium.

These elements are all bound together in the form of silicate rocks, all of which take the form of oxides. The most common is Silicon dioxide - SiO2 at 48%, followed by Magnesium Oxide - MgO at 37.8%. Examples of rocks that you might find inside the mantle include: olivine - (Mg,Fe)2SiO4, pyroxenes - (NaCa)(Mg,Fe,Al)(Al,Si)2O6, spinel - MgAl₂O₄, and garnet - general chemical formula A3B2Si3O12, where A is a divalent cation (Fe2+, Ca2+, Mg2+, Mn2+) and B is a trivalent cation (Fe3+, Al3+, Cr3+).


From above the crust consists of:
oxygen - - 44.8%
magnesium - 22.8%
silicon - - 21.5%
- - - - - = 89.1%
iron
aluminum
calcium
sodium
potassium
- another - 10.9% - ALL still within our 16 most common elements!
##############
Silicate Rocks

SiO2 - 48%
MgO -. 37%
- - - 85%

That + what is melted from the crust above is what normally comes out of volcanoes as basalt, andesite, granite, obsidian and rhyolite.

Sure, some limited accumulations can occur BUT -
Anything beyond these amounts had to arrive later by some impact event in the area.

The impact craters may have eroded away or been scraped off in subduction, but the exotic elements remain out of place.

EXAMPLES:

1. 3,000 Ma Stillwater Montana Crater Complex USA - 300km in Diameter, oldest known surviving crater. Deformed by the Sudbury Impact (1849 Ma) and Penokean orogeny (1890-1830 Ma), the Mazatzal orogeny (1700-1600 Ma), the Grenville orogeny (1400 - 1000 Ma)
- platinum, palladium, rhodium

2. 2,023 Ma Vredefort crater in South Africa, 300 km (190 mi)
- gold, platinum, palladium, ruthinium

3. 1,850 Ma Sudbury Crater - Ontario, Canada 250 km (160 mi)
Subsequent geological processes have also deformed the crater into its current smaller oval shape.
- nickel, copper, platinum, palladium, gold, and rare Earth metals.

4. ? Norilsk Russia is the center of a region where nickel, copper, cobalt, platinum, palladium and coal are mined.

5. 140 Ma Upheaval Dome Utah 6 km - vanadium, uranium, tantalum, niobium.

6. 65 Ma Chicxulub crater in Yucatan, Mexico 180 km (110 mi). World wide layer of iridium.





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