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Compared to the Solar System as a whole, Earth is depleted in volatile elements, such as hydrogen, carbon, and nitrogen, which likely never condensed on planets formed in the inner, hotter, part of the Solar System.
Earth is also depleted in moderately volatile elements, such as silver.
“But these meteorites have compositions that are very volatile-rich, unlike the Earth, which is volatile-depleted.” The silver isotopes also presented another riddle, suggesting that the Earth’s core formed about 5-10 million years after the origin of the Solar System, much earlier than the date from the hafnium-tungsten results.
The group concludes that these contradictory observations can be reconciled if Earth first accreted volatile-depleted material until it reached about 85% of its final mass and then accreted volatile-rich material in the late stages of its formation, about 26 million years after the Solar System’s origin.
All naturally occurring hafnium-182 decayed within the first 50 million years of Earth's history, leaving tungsten-182 in its place.
Tungsten and hafnium behaved very differently during the planet's first 50 million years.
On its own, the tungsten isotope ratio is interesting, but not enough to make any convincing conclusions.
But the researchers also observed that the same rocks contain an unusual ratio of helium isotopes.
Tiny variations in the isotopic composition of silver in meteorites and Earth rocks are helping scientists put together a timetable of how our planet was assembled beginning 4.568 billion years ago.
The new study, published in the journal , indicates that water and other key volatiles may have been present in at least some of Earth’s original building blocks, rather than acquired later from comets, as some scientists have suggested.
The researchers are not yet sure how Earth's mantle preserved these anomalies.Tags: Adult Dating, affair dating, sex dating