外地核的外界是以古登堡一魏彻特间断面(深约2900公里)与地幔分界。这一间断面是固态一液态相变面，在其下s波消失，指示外地核是熔融的。内，外地核的界线大约在5145公里深，界面清楚，肯定是液态一固态相变处。
有证据表明，外地核的密度约为地幔物质的两倍。
Evidence indicates that the outer core is about twice as dense as the material in the mantle.
有人认为外地核主要是由在高温下处于熔态的铁和镍构成的。
The outer core is believed to be composed mostly of iron and nickel in a molten state at a very high temperature.
因此，眼球构造可能是外地核向地幔释放氧，下地幔内存在氧元素的历史记录。
The eyeball structures might have recorded the history of oxygen activity in the mantle and the Earth's core.
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