The mystery of the disappearing iridium

[Big Bad Voodoo]

Why do these space rocks have such a high level of it, while the Earth is impoverished?

http://io9.com/5983593/the-mystery-of-the-disappearing-iridium

[pallidin]

It's not impoverished, it's just hidden. From the article you cited:

"The main clue to iridium's vanishing act is the fact that it is densest element possible. While others elements are larger, in terms of protons and neutrons, you can't beat iridium for team spirit. The individual atoms cluster together like they're repelling an invasion. The next clue is that it seems to team up almost exclusively with other dense elements, like platinum and iron. Both are elements that we tend to have to dig for.

If iridium came on space rocks, it had to be here since the beginning, but unlike other material, it couldn't stay up top. While the Earth was still no more than a molten aggregate of space rocks itself, iridium inevitably and irretrievably shifted farther and farther down towards its center. It also combined with iron - which did little to lighten it. Like Atlantis, it sank beneath the sea (and the crust and the mantel), leaving the surface of the Earth mostly iridium free. So while we do actually have plenty of iridium on Earth, it's nowhere we could get to it. Better to try to snatch it out of the sky."

Edited February 16, 2013 by pallidin

[sepulchrave]

Actually osmium is the densest element. Iridium is the second densest. But I quibble.