地球內核形成於10至15億年前

原文網址：www.sciencedaily.com/releases/2015/10/151007135656.htm

Earth's inner core was formed 1-1.5 billion years ago

地球內核形成於10至15億年前

There have been many estimates for when the earth's inner core was formed, but scientists from the University of Liverpool have used new data which indicates that the Earth's inner core was formed 1 -- 1.5 billion years ago as it "froze" from the surrounding molten iron outer core.

過往對於地球內核何時形成有許多的猜測。近日，利物浦大學的科學家利用新證據推測地球的內核約在10至15億年前，從周遭的鐵質液態外核中「冷卻」而生。

The inner core is Earth's deepest layer. It is a ball of solid iron just larger than Pluto which is surrounded by a liquid outer core. The inner core is a relatively recent addition to our planet and establishing when it was formed is a topic of vigorous scientific debate with estimates ranging from 0.5 billion to 2 billion years ago.

內核在地球的分層構造中是最深的一層，為一顆比冥王星略大的固體鐵球，被液態的外核環繞。相較其它構造，內核加入地球是起較近代的事件，而確認它的形成時間也是一件討論十分熱烈的科學議題。過往科學家對此時間的預估從5億至20億年前不等。

In a new study published in Nature, researchers from the University's School of Environmental Sciences analysed magnetic records from ancient igneous rocks and found that there was a sharp increase in the strength of the Earth's magnetic field between 1 and 1.5 billion years ago.

在發表於《自然》的新研究中，利物浦大學環境科學院的研究人員分析了古代火成岩中的地磁記錄，並發現在10到15億年前地球磁場強度有突然上升的現象。

This increased magnetic field is a likely indication of the first occurrence of solid iron at Earth's centre and the point in Earth's history at which the solid inner core first started to "freeze" out from the cooling molten outer core.

劇烈上升的磁場強度可能代表在地球中心有第一塊固體鐵產生，而象徵著在地球歷史上，逐漸冷卻的外核開始「冷卻」出固態內核的時刻。

Liverpool palaeomagnetism expert and the study's lead author, Dr Andy Biggin, said: "This finding could change our understanding of the Earth's interior and its history."

利物浦大學的古地磁專家，也是本研究的第一作者Andy Biggin博士說：「這項發現有可能會改變我們對地球內部與其歷史的認知。」

"The timing of the first appearance of solid iron or "nucleation" of the inner core is highly controversial but is crucial for determining the properties and history of the Earth's interior and has strong implications for how the Earth's magnetic field -- which acts as a shield against harmful radiation from the sun, as well as a useful navigational aid -- is generated.

「內核的固態鐵首次出現，或「成核」(nucleation)的時間是件備受爭議的議題，它對瞭解地球內部的性質和歷史來說相當重要。而地磁作為可以抵擋來自太陽的有害輻射的屏障，同時也是指引航道的利器，在探討地磁是如何產生的這一方面，它也具有相當重大的意義。」

"The results suggest that the Earth's core is cooling down less quickly than previously thought which has implications for the whole of Earth Sciences. It also suggests an average growth rate of the solid inner core of approximately 1mm per year which affects our understanding of the Earth's magnetic field."

「結果顯示地核的冷卻速率較之前認為的還要慢，這對整個地球科學界有相當重要的啟發。另外結果也指出固態內核成長的平均速率約為每年1mm，而影響我們對地磁的理解。」

The Earth's magnetic field is generated by the motion of the liquid iron alloy in the outer core, approximately 3,000 km beneath the Earth's crust. These motions occur because the core is losing heat to the overlying solid mantle that extends up to the crust on which we live producing the phenomenon of convection.

地磁是由於在地殼下約3000公里處，外核中的液態鐵合金運動而產生。會產生這種運動則是由於地核會向覆蓋於上方的地函散熱，而導致對流現象。地函的延伸範圍為地核至我們所居住的地殼之下。

Once the inner core started to freeze, this convection received a strong boost in power because light, non-metallic elements remained molten in the outer core and were buoyant relative to the overlying liquid. The process continues today and is thought to be the main source of "fuel" for generating the Earth's magnetic field.

一旦內核開始凝結而成，便會產生更強的能量推動這種對流效應，因為較輕盈的非鐵質元素會殘留在融化的外核中，相較於周遭的液體會往上浮動。這種過程在今日仍持續著，並被視為地球磁場的主要「燃料」來源。

Dr Biggin added: "The theoretical model which best fits our data indicates that the core is losing heat more slowly than at any point in the last 4.5 billion years and that this flow of energy should keep the Earth's magnetic field going for another billion years or more.

Biggin博士附加說明：「最符合我們數據的理論模型指出在45億年來的任何時刻，地核流失熱量的速度都比過往認為的還要慢，而此能量流動應該還能繼續支持地球磁場至下一個10億年或是更久。」

"This contrasts sharply with Mars which had a strong magnetic field early in its history which then appears to have died after half a billion years."

「這跟火星是強烈的對比。火星在它的行星歷史早期擁有強烈的磁場，但似乎僅維持了五億年就嘎然而止。」

The study, published in the journal Nature, is a collaboration between scientists at the Universities of Liverpool, Helsinki, Michigan Tech, UC San Diego, and the Chinese Academy of Sciences.

此篇發表於期刊《自然》的研究為利物浦大學、赫爾辛基大學、密西根理工大學、加州大學聖地牙哥分校和中國科學院的科學家之間的合作成果。

引用自：University of Liverpool. "Earth's inner core was formed 1-1.5 billion years ago." ScienceDaily. ScienceDaily, 7 October 2015.