An early geodynamo driven by exsolution of mantle components from Earth's core.
An early geodynamo driven by exsolution of mantle components from Earth's core.
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DOI：
10.1038/nature18594
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发表时间：
2016-08-18
期刊：
影响因子：
64.8
通讯作者：
Nimmo F
中科院分区：
文献类型：
--
作者：
Badro J;Siebert J;Nimmo F
陆地地核的形成发生在熔融地球的早期，这是由于不相容的金属和硅酸盐熔体的引力分离，从硅酸盐地幔中剥离出亲铁元素到金属地核，留下了亲岩石的成分。在这里，我们进行的实验表明，在足够高的温度下，地球上喜爱岩石的主要成分氧化镁也可以溶解在形成地核的金属熔体中。我们的数据清楚地指向溶解反应，并且与最近的DFT计算一致。利用地核形成模型，我们进一步表明，地球吸积期间的高温事件（如月球形成的巨大撞击）可以为早期地核贡献大量的镁。当它随后冷却时，随之而来的浮力氧化镁的溶解产生了大量的引力能。这种能量与内核凝固产生的能量相当，如果不是明显更高的话——内核凝固是地球当前磁场的主要驱动力。由于内核太年轻，无法解释约10亿年前古磁场的存在，我们的结果解决了最近对至少3.45 Gyr的古磁场的古地磁观测所提出的难题。
Terrestrial core formation occurred in the early molten Earth by gravitational segregation of immiscible metal and silicate melts, stripping iron-loving elements from the silicate mantle to the metallic core, and leaving rock-loving components behind. Here we performed experiments showing that at high enough temperature, Earth’s major rock-loving component, magnesium oxide, can also dissolve in core-forming metallic melts. Our data clearly point to a dissolution reaction, and are in agreement with recent DFT calculations. Using core formation models, we further show that a high-temperature event during Earth’s accretion (such as the Moon-forming giant impact) can contribute significant amounts of magnesium to the early core. As it subsequently cools, the ensuing exsolution of buoyant magnesium oxide generates a substantial amount of gravitational energy. This energy is comparable to if not significantly higher than that produced by inner core solidification — the primary driver of the Earth’s current magnetic field. Since the inner core is too young to explain the existence of an ancient field prior to ~1 billion years, our results solve the conundrum posed by the recent paleomagnetic observation of an ancient field at least 3.45 Gyr old.