Meteorites delivered gold to Earth
A burst of meteorite impacts around 3.9 billion years ago delivered precious metals to Earth
Scientists have shown that the Earth's surface became enriched with precious metals by impacting meteorites.
Scientists have shown that the Earth's surface became enriched with precious metals by impacting meteorites.
The Earth's crust and mantle has considerably more gold than expected from favored models of planetary formation.
A study from the University of Bristol looked at some of the oldest rocks on Earth, demonstrating that gold was delivered by meteorites long after their formation.
Their results are published in Nature.
While the Earth was forming, iron sank to the centre of the planet, forming the core.
Any precious metals in the planetary mix would have gone with this iron and concentrated in the core, leaving the mantle devoid of elements such as gold, platinum, and osmium.
But this is not what we observe. In fact, the silicate mantle has up to 1,000 times more gold than anticipated.
Several reasons for this enrichment were proposed in the past, including delivery by meteorites, although until now it has not been possible to prove.
By measuring isotopes in rocks that are nearly four billion years old from Greenland, the team has managed to date the gold delivery, and to relate it to an event known as the "terminal bombardment".
read more: http://www.bbc.co.uk/news/science-environment-14827624#story_continues_1
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