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

閱讀難度：

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. （點擊BBC網(wǎng)站查看原文）

天外來客送黃金

?????? 據(jù)英國廣播公司報道，英國布里斯托大學的一項研究顯示，隕石雨為地球表面帶來了豐富的貴金屬。

???????研究人員通過分析地球上最古老的巖石得出結論：黃金是地球形成很久以后由隕石雨帶來的。

???????地球形成過程中，鐵沉降到地球中心構成地核，地球的貴金屬也都隨著鐵一起沉入地核，導致地幔中沒有留下金、鉑和鋨等元素。

(China.org.cn September 15, 2011)