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当水在核幔边界遇到铁
简单来说，地球自外而内分别由一层较薄的地壳、一层较厚的地幔和中心的大铁球地心所组成。地球表面的大洋大海中富集着大量的水，它们其中的一部分会与岩石反应生成所谓的含水矿物而进入地球内部，甚至深入地幔。当它们达到地幔底部进而遇到地心的时候，到底会发生什么样的变化？来自HPSTAR的毛河光院士带领的研究小组在最新一期的National Science Review (DOI: 10.1093/nsr/nwx109) 发表了对这一课题的最新研究成果（标题摘要如下）。
“当水在地幔底部遇见铁，它们会发生化学反应生成一种高度氧化的矿物”，毛院士指出。该小组将一小片铁和水组成的样品至于下地幔的温压条件下（大约96万大气压，2000摄氏度），发现生成了FeO2Hx和氢化铁。同时研究认为任意的铁氧化物和水之间都存在类似的化学反应。由于地核可以提供接近于无限的铁，当水源源不断被输送到地幔深部，氧元素以FeO2Hx的形式在地核上部慢慢积聚。
同时他们发现当氧元素积聚的同时，氢元素则从水中分离出来并最终回到地球表面。
“高度氧化的FeO2Hx在地幔中是不稳定的”毛院士指出，“当它到达一个临界点的时候，可能会爆发大面积的氧气爆发，最终导致地球表面的气候变化。”
地球内部的氢氧循环
When water meets iron at Earth's core-mantle boundary
Hydrous minerals in subducted crust can transport large amounts of water into Earth's deep mantle. Our laboratory experiments revealed the surprising pressure-induced chemistry that when water meets the iron at the core-mantle boundary, they react to form an interlayer with an extremely oxygen-rich form of iron, iron peroxide, together with iron hydride. Hydrogen in the layer will escape upon further heating and rise to the crust, sustaining the water cycle. With water supplied by the subducting slabs meeting the nearly inexhaustible iron source in the core, an oxygen-rich layer would cumulate and thicken, leading to major, global consequences in our planet. The seismic signature of the D” layer may echo the chemical complexity of this layer. Over the course of geologic time, the enormous oxygen reservoir accumulating between the mantle and core may have eventually reached a critical eruption point. Very large scale oxygen eruptions could possibly cause major activities in the mantle convection and leave evidences such as the rifting of supercontinents and the Great Oxidation Event.
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