Core formation, Hadean mattes and the timescale of Earth accretion

核心形成、冥古宙遮罩和地球吸积的时间尺度

• 批准号: NE/F018266/1
• 负责人: Bernard Wood
• 金额: $ 46.8万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF018266%2F1
• 关键词: Core; formation; Hadean; mattes; timescale

Based on radioactive dating of the oldest particles in meteorites it appears that the planets began to form 4567 Million years ago from a cloud of dust and gas surrounding the young sun. We are currently at a very interesting and exciting time for those scientists trying to understand how the Earth and the other planets grew from this primitive solar system material. It has recently been discovered that there were a number of short-lived radioactive isotopes which were present at the beginning of the solar system, possibly injected into the dust cloud by a nearby exploding star. These radioactive isotopes are now completely decayed ('extinct') but their stable decay products ('daughters') can be found in meteorites and in the Earth, moon and Mars. Because the extinct isotopes and their daughters have different chemical properties, they may be used to investigate early processes which tended to separate them. For example, hafnium-182 (extinct) decays to tungsten-182 with a half-life of 9 million years. Tungsten tends to enter the metal cores of planets while hafnium remains in their outer 'rocky' parts. From measuring the isotopes of daughter tungsten in meteorites and the planets it has been shown that some asteroids formed metal cores within 1-2 million years of the beginning of the solar system while the same processes took about 12 million years on Mars and 30 million years on Earth. The aim of this project is to investigate the chemical behaviour of a number of these extinct isotopes and their daughters so that we may better understand the processes which took place as the Earth grew. One major question is whether or not the Earth lost a substantial fraction of those elements which could easily be turned into gases ('volatile') at the time of the giant impact which appears to have formed the moon about 50 million years after the beginning of the solar system. Another is the apparent discrepancy between the time of core separation on Earth measured by the hafnium-182, tungsten-182 system discussed above and that measured by uranium-lead. Lead is somewhat volatile, so it is possible that the age measured by lead isotopes (50-100 million years after the beginning of the solar system) is actually the age of volatile loss rather than the age of core formation. We will be able to distinguish between these possibilities by determining the chemical behaviour of parent and daughter isotopes of different volatility during the core formation stage. In order to do this I propose to work on distribution of lead (daughter of uranium and parent of thallium), thallium (daughter of lead-205) and silver (daughter of palladium-107) during metal core segregation under the high pressure, high temperature conditions relevant to the growing Earth. Because the three daughter elements have quite different volatilities (thallium most, silver least) the results will enable us to separate the two processes of core separation and volatile loss.

基于陨石中最古老的颗粒的放射性约会，看来这些行星在年轻的太阳周围的尘埃和气体云中开始形成4.67亿年。对于那些试图了解地球和其他行星如何从这种原始的太阳系材料中增长的科学家来说，我们目前正处于非常有趣和激动人心的时刻。最近发现，在太阳系开头存在许多短寿命的放射性同位素，可能会被附近的爆炸恒星注射到尘埃云中。这些放射性同位素现在已经完全腐烂（“灭绝”），但是它们稳定的衰减产品（“女儿”）可以在陨石以及地球，月亮和火星中找到。由于灭绝的同位素及其女儿具有不同的化学特性，因此它们可用于调查往往会将其分开的早期过程。例如，Hafnium-182（灭绝）以900万年的半衰期衰减到​​Tungsten-182。钨倾向于进入行星的金属岩心，而Hafnium仍留在其外部“岩石”部分。通过测量陨石中女儿钨的同位素和行星，已经表明，某些小行星在太阳系开始后的1-200万年内形成了金属核心，而同一过程在火星上花费了约1200万年的地球，地球上花费了大约1200万年。该项目的目的是调查许多这些灭绝的同位素及其女儿的化学行为，以便我们可以更好地了解随着地球成长而发生的过程。一个主要的问题是，在巨大撞击时，地球是否损失了很容易变成气体（“挥发性”）的大部分，这些元素似乎在太阳系开始后约有5000万年形成了月球。另一个是通过Hafnium-182测得的地球分离时间，Tungsten-182系统与铀铅测量之间的明显差异。铅有些波动，因此，铅同位素（太阳系开始后500-1亿年）测量的年龄实际上是挥发性损失的年龄，而不是核心形成的年龄。我们将能够通过确定核心形成阶段的父母和女儿同位素的化学行为来区分这些可能性。为了做到这一点，我建议在金属核心分离期间在高温下，高温条件在金属核心隔离期间分配铅（铀的女儿和thallium的女儿），thallium（铅-205的女儿）和银（Palladium-107的女儿）和银（Palladium-107的女儿）。由于三个女儿元素具有完全不同的波动性（最少，最少的thallium），因此结果将使我们能够将核心分离和挥发性损失的两个过程分开。

项目成果

The Early Earth - Accretion and Differentiation

早期地球 - 吸积和分化

• DOI: 10.1002/9781118860359.ch4
• 发表时间: 2015
• 作者: Morbidelli A

The effects of composition and temperature on chalcophile and lithophile element partitioning into magmatic sulphides

• DOI: 10.1016/j.epsl.2015.05.012
• 发表时间: 2015-08-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Kiseeva, Ekaterina S.;Wood, Bernard J.
• 通讯作者: Wood, Bernard J.

Geophysics. How did Earth accrete?

地球物理学。

• DOI: 10.1126/science.1172587
• 发表时间: 2009
• 期刊: Science (New York, N.Y.)
• 作者: Halliday AN

Vanadium isotopic difference between the silicate Earth and meteorites

• DOI: 10.1016/j.epsl.2013.12.030
• 发表时间: 2014-03
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: S. Nielsen;J. Prytulak;B. Wood;A. Halliday

The effect of sulfur on the partitioning of Ni and other first-row transition elements between olivine and silicate melt

• DOI: 10.1016/j.gca.2010.08.014
• 发表时间: 2010-11
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: J. Tuff;H. O’Neill