對地核成分的新見解

原文網址：www.sciencedaily.com/releases/2015/09/150922151604.htm

A new view of the content of Earth's core

對地核成分的新見解

There is more oxygen in the core of Earth than originally thought. Lawrence Livermore geologist Rick Ryerson and international colleagues discovered some new findings about Earth's core and mantle by considering their geophysical and geochemical signatures together. This research provides insight into the origins of Earth's formation.

地核的含氧量比原先所認為的還要高。勞倫斯利福摩爾國家實驗室的地質學家Rick Ryerson與其他國際研究人員統合了地函與地核的地球物理和地球化學訊號，而有了新發現。此研究有助於瞭解地球如何形成。

Based on the higher oxygen concentration of the core, Ryerson's team concludes that Earth must have accreted material that is more oxidized than the present-day mantle, similar to that of planetesimals such as asteroidal bodies. A planetesimal is an object formed from dust, rock and other materials and can be can be anywhere in size from several meters to hundreds of kilometers.

Ryerson的團隊根據較高的地核含氧量推測，吸積(accrete)成地球的原料擁有比現今地函還要高的氧化程度，可能與小行星之類的微行星(planetesimal)相似。微行星是由塵埃、岩石或者其他物質所組成的星體，大小可從數公尺到上百公里不等。

Earth formed about 4.56 billion years ago over a period of several tens of millions of years through the accretion of planetary embryos and planetesimals. The energy delivered by progressively larger impacts maintained Earth's outer layer and an extensively molten magma ocean. Gravitational separation of metal and silicate within the magma ocean results in the planet characterized by a metallic core and a silicate mantle.

地球經歷了數千萬年的行星胚與微行星加積過程後，約在45.6億年前形成。越發強勁的撞擊所傳遞出來的能量使得地球外層變成一片浩瀚無垠的岩漿海。發生在其中的重力分離作用分離了金屬與矽酸鹽，造成地球的地核與地函分別由金屬和矽酸鹽組成。

The formation of Earth's core left behind geophysical and geochemical signatures in the core and mantle that remain to this day. In the past, core formation models have only attempted to address the evolution of core and mantel compositional signatures separately rather than looking for a joint solution.

在這過程中刻劃於地核和地函的地球物理與地球化學訊號，我們時至今日仍能偵測的到。過去的地核形成模型在瞭解地核與地函的成分如何演變時，是將它們分開處理，而非將兩者視為一個聯合體系。

By combining experimental petrology, geochemistry, mineral physics and seismology, the team found that core formation occurred in a hot (liquid) moderately deep magma ocean not exceeding 1,800-kilometer depth, under conditions more oxidized than present-day Earth.

結合了實驗岩石學、地球化學、礦物物理學和地震學，研究團隊發現地核形成於一座炎熱(液態)、深度適中而不超過1800公里深的岩漿海，環境中氧化程度較目前的地球要高。

"This new model is at odds with the current belief that core formation occurred under reduction conditions," Ryerson said. "Instead we found that Earth's magma ocean started out oxidized and has become reduced through time by oxygen incorporation into the core."

「這個新模型的奇特之處在於它與目前認為地核形成於還原環境下的說法相悖。」Ryerson說。「反之，我們發現地球的岩漿海在形成時處於氧化態，隨著時間流逝，氧慢慢的與地函結合，造成岩漿海越趨還原。」

They found the oxygen concentrations in the core are higher than previously thought and silicon concentrations are lower than previous estimates.

他們發現與之前的預測相比，地核的氧含量較高而矽酸鹽含量則較低。

引用自：DOE/Lawrence Livermore National Laboratory. "A new view of the content of Earth's core." ScienceDaily. ScienceDaily, 22 September 2015.