A burst of meteorite impacts around 3.9 billion years ago delivered precious metals to Earth. [Agencies]

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A study from the University of Bristol has shown that the Earth's surface became enriched with precious metals by impacting meteorites, BBC reported.

The researchers, who looked at some of the oldest rocks on Earth, concluded that gold was delivered by meteorites long after the Earth's formation.

While the Earth was forming, iron sank to the centre of the planet, forming the planet's 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, researchers said. （点击BBC网站查看原文）

天外来客送黄金

       据英国广播公司报道，英国布里斯托大学的一项研究显示，陨石雨为地球表面带来了丰富的贵金属。

       研究人员通过分析地球上最古老的岩石得出结论：黄金是地球形成很久以后由陨石雨带来的。

       地球形成过程中，铁沉降到地球中心构成地核，地球的贵金属也都随着铁一起沉入地核，导致地幔中没有留下金、铂和锇等元素。

(China.org.cn September 15, 2011)