This is from a discussion on another list I am on, however, because it deals with meteorite composition, I thought I'd pass it along. It is the foundation for understanding why we use isotope ratios to determine where in our solar system a given meteorite may have originated.
In the discussion of dwarf stars having giant diamond crystals at their cores, the question was raised, "Are there any statistics on distribution of elements in our solar system"? Yes, There is a concept called Cosmic(Universal) Abundance of Elements <http://www.doane.edu/crete/academic/science/chem/Ast/Astro.html> This illustration is interactive and overlain on the Andromeda Galaxy for effect but it pertains to all mass in the universe. Using spectral band measurements astronomers were able to sum up the elemental ratios of the cosmos
It was correctly mentioned that elements heavier than iron are formed in supernovae and all in a very short time. However, the ratios of light elements to heavy ones are also biased by the number of hydrogen particles combined to form a heavy element. (e.g. Roughly it takes 92 Tritium atoms to form one Uranium atom.) Working backwards, adding up all the atomic masses of all the material in our solar system, would approximate the number of hydrogen/helium atoms in our solar precesseor.
For a bar graph representation of abundance (standardized as ratios to silicon atoms), see <http://jchemed.chem.wisc.edu/JCESoft/Programs/PTL/Sample/Plots/univabnd.html> .
Below our feet, there is an terrestrial abundance <http://www.daviddarling.info/encyclopedia/E/elterr.html>
which is actually an estimate of the abundance in the lithosphere(crust and upper mantle). This does not include the deep mantle or core.
There was a sorting of the elements in our proto-solar system with the heavier elements dominating the inner system and the volatiles the outer edge. There are two mechanisims theorized as to how this occured(They were probably co-dynamic). One concept is that the proto-solar system, left over from the supernova of our sun's precesseor , scattered the elements evenly over an approximately 100AU wide disk. The heavier elements precipitated before the more volatiles due to the faster cooling rate on the edge of the protodisk and fell back toward the gravitational center of our solar system to be incorporated into the inner planets. This illustration correlates formation temperature of minerals and planet distances from the sun. <http://www.geology.uiuc.edu/~hsui/classes/geo116/lectures/wk2folder/compodist-demo.html>
The other mechanism contends that the mixture of elements was sorted by pressure waves -- an allegory to the solar wind, by tending to sweep lighter elements toward the outer rim. This theory is supported by such evidence as ratios of heavy to light isotopes decreasing with distance from the center of the solar system.
Someone, I recall, rasied a question about the the amount of iron in meteorites perhaps being higher than expected given that free iron is a deep core occurrence. Irony meteorites represent the cores of asteroids large enough gravationally and thermally to have allowed to nickel-iron to sort to the center/core of the asteroid. We find these meteorites because cosmic collisions opened up the cores of these asteroids and flung the iron centers far and wide. Stoeny meteorites--specifically Common Chondrites, have flakes of free nickel-iron metal because the iron blebs which were incorporated into pyroxene/olivine matrix, come from bodies which were to small to 1) keep warm enough long enough for the nickel-iron to melt and 2) the internal gravitational pull on these small bodies was insufficient to draw the nickel-iron to the core.
Regards, Elton
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