The oldest impact deposits on Earth - First confirmation of an extraterrestrial component
The oldest impact deposits on Earth - First confirmation of an extraterrestrial component
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地球上最古老的撞击沉积物——首次确认地外成分
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
G. Byerly
中科院分区：
文献类型：
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作者：
A. Shukolyukov;F. Kyte;G. Lugmair;D. Lowe;G. Byerly
南非巴伯顿绿岩带早太古代（3.22 Ga）球粒层（S4）中的铬同位素组成与背景岩石和其他陆地样品中的铬同位素组成不同。这积极证实了该床中存在外星成分，并支持了撞击起源的假设。外星铬的来源最有可能是碳质球粒陨石，可能是CV品种。根据铬同位素和铂族元素，估计这个小球床中的外星成分约为15%。由于这在许多方面与第三纪撞击的全球沉降物相似，我们推断它们有相似的起源。然而，在太古代球粒床陨石物质的总量是大约30倍以上，在第三纪沉积物，这意味着一个更大的抛射体，可能20公里或更大的直径。
The chromium isotopic compositions of samples from an early Archean (3.22 Ga) spherule bed (S4) from the Barberton Greenstone Belt, South Africa, are distinct from that in background rocks and other terrestrial samples. This positively confirms the presence of an extraterrestrial component in this bed and supports hypotheses of an impact origin. The source of the extraterrestrial Cr is most likely to be a carbonaceous chondrite, probably of the CV variety. The estimated extraterrestrial component in this spherule bed is about 15% based on Cr isotopes and platinum group elements. Since this is similar in many regards to the global fallout from the Cretaceous-Tertiary impact, we infer that they have a similar origin. However, the total amount of meteoritic material in the Archean spherule bed is about 30 times greater than in Cretaceous-Tertiary deposits, implying a much larger projectile, possibly 20 km or more in diameter.