地函是層在地殼下方的岩石，也是地球的組成中佔比最大的部分。最近科學家首度從地函取回一段相當長的岩石紀錄。
海洋鑽探船「聯合果敢號」2023年春季進行了航次399「生命基石——亞特蘭提斯地塊」。期間船上的科學家取出了一段延續將近1268公尺長的地函岩石。(圖片來源：Thomas Ronge)
團隊表示這段岩石有助於闡明某些謎題，像是地函在生命起源過程中扮演的腳色、地函熔化產生火山活動的過程、它如何驅動重要的元素(像是碳與氫)在地球各處循環流動。
海洋鑽探船「聯合果敢號」2023年春季進行了航次399「生命基石——亞特蘭提斯地塊」。期間船上的科學家從位於大西洋中洋脊附近、露出下方地函岩石的海床——就像是一扇「窗口」的地質構造中取出了這段延續將近1268公尺長的地函岩石。
這項破紀錄的成就是由「國際海洋發現計畫」主持，其為二十幾個國家組成的聯合研究組織。他們從世界各處的海床取出岩芯(圓柱狀的沉積物與岩石樣品)來解讀地球的歷史。該計畫嘗試取出地函岩石的行動可以追溯自1960年代早期。
從那時起，這群科學考察團隊已經彙整了一系列從地函取回的岩石，並且探討其成分、構造以及形成背景。
他們發表在期刊《科學》的最新發現對於這些岩石的融化歷程，得到了比預期中更加全面的成果。
卡地夫大學地球與環境科學院的教授Johan
Lissenberg是研究主要作者，他說：「我們去年取得的這段地函岩芯本身已經是地球科學史上的一大成就，然而不僅如此，蘊藏在其中的事物可以告訴我們地球是由什麼組成，又經過什麼樣的演變，這才是它的貴重之處。」
「我們的研究首先把這些岩石的礦物學特性以及化學組成記錄下來，藉此分析地函的成分。」
「結果跟原先預期的不同。這些岩石的輝石礦物少了很多，而鎂的濃度則非常高——兩者皆是岩石熔融程度遠超出我們的預測才會有的結果。」
當地函從地球較深的地方往地表上升，過程中就會發生岩石熔融。
研究人員主張進一步地分析此作用，或許能讓我們對於岩漿的形成過程及岩漿造成的火山活動得到重要的觀點。
「我們也發現了熔融物質在地函內部運輸的通道，使得我們可以追蹤岩漿形成之後的經歷以及它往地球表面上升的過程。」
「這項發現的重要之處在於它告訴了我們地函產生熔融物質並供應給火山的過程，尤其是位在海床上的火山——地球大多數的火山活動都發生於此。成功取得這些地函岩石使我們未來可以把火山及岩漿的最初來源連結起來。」
研究的另外一項初步結果，是呈現了地函岩石中含量相當豐富的橄欖石礦物如何跟海水發生一連串的化學反應，產生氫氣與其他可以點燃生命之火的分子。
科學家相信這些化學反應可能是奠定地球生命起源的作用之一。
伍茲霍爾海洋研究所地質與地球物理部門的副研究員Susan
Q. Lang是該航次的共同主持人，她所參與的團隊也正在持續對岩石和液體樣品進行分析。「相較於形成現今陸地而較為常見的岩石，出現在早期地球的岩石組成更類似於我們在這班航次中取得的岩石，」她說。
「相較於形成現今陸地而較為常見的岩石，出現在早期地球的岩石組成更類似於我們在這班航次中取得的岩石，」研究人員表示。(圖片來源：Johan Lissenberg)
「分析它們可以讓我們對地球歷史早期的物理化學環境得出重要的見解，以及哪些環境可以在長久的地質時間當中持續提供生命誕生的有利條件，因而成為最早的生命形式存活的地方。」
登上這班「聯合果敢號」航次的國際團隊成員包含了30幾位科學家，他們將持續研究這根岩芯以解開許多不同方面的難題。
里茲大學地球與環境學院的副教授Andrew
McCaig博士是航次399的主要提案人，也是該航次的共同主持人。「我們在2018年首度提出航次399的計畫，希望寫在這篇論文的成果可以讓至今所有參與在內的同仁引以為榮，」他說。
「對於探討地函熔融過程、岩石與海洋的化學物質交換、有機地球化學、微生物學……等各方面的研究領域來說，我們這根深度極深的新岩芯在未來數十年都會被當作標準剖面來用。」
「任何人都可以取用這班航次得到的所有資料，這也是一個跨國科學研究應該如何進行的典範。」
他們發表在《科學》的論文題目為「A
long section of serpentinized depleted mantle peridotite」(一根蛇紋岩化的虧損地函橄欖岩的長段剖面)。
Record-breaking recovery of rocks that
originated in Earth’s mantle could reveal secrets of planet’s history
Scientists have recovered the first long
section of rocks that originated in the Earth’s mantle, the layer below the
crust and the planet’s largest component.
The rocks will help unravel the mantle’s role in the
origins of life on Earth, the volcanic activity generated when it melts, and
how it drives the global cycles of important elements such as carbon and
hydrogen, according to the team.
The nearly continuous 1,268 metres of mantle rock was
recovered from a “tectonic window,” a section of the seabed where rocks from
the mantle were exposed along the Mid-Atlantic Ridge, during Expedition 399
“Building Blocks of Life, Atlantis Massif” of the ocean drilling vessel JOIDES
Resolution in Spring 2023.
With attempts dating back to the early 1960s, the
recovery was a record-breaking achievement led by the International Ocean
Discovery Program, an international marine research consortium of more than 20
countries that retrieves cores—cylindrical samples of sediment and rock—from
the ocean floor to study Earth’s history.
Since then, the expedition team has been compiling an
inventory of the recovered mantle rocks to understand their composition,
structure and context.
Their findings, presented in the journal Science, reveal a more extensive history
of melting in the recovered rocks than expected.
Lead author Professor Johan Lissenberg from Cardiff
University’s School of Earth and Environmental Sciences, said: “When we
recovered the rocks last year, it was a major achievement in the history of the
Earth sciences, but, more than that, its value is in what the cores of mantle
rocks could tell us about the makeup and evolution of our planet.
“Our study begins to look at the composition of the
mantle by documenting the mineralogy of the recovered rocks, as well as their
chemical makeup.
“Our results differ from what we expected. There is a
lot less of the mineral pyroxene in the rocks, and the rocks have got very high
concentrations of magnesium, both of which results from much higher amounts of
melting than what we would have predicted.”
This melting occurred as the mantle rose from the
deeper parts of the Earth towards the surface.
Results from further analysis of this process could
have major implications for the understanding of how magma is formed and leads
to volcanism, the researchers claim.
“We also found channels through which melt was
transported through the mantle, and so we are able to track the fate of magma
after it is formed and travels upwards to the Earth’s surface.
“This is important because it tells us how the mantle
melts and feeds volcanoes, particularly those on the ocean floor that account
for the majority of volcanism on Earth. Having access to these mantle rocks
will allow us to make the connection between the volcanoes and the ultimate
source of their magmas.”
The study also provides initial results on how
olivine, an abundant mineral in mantle rocks, reacts with seawater, leading to
a series of chemical reactions that produce hydrogen and other molecules that
can fuel life.
Scientists believe this might have been one of the
underpinning processes in the origin of life on Earth.
Dr Susan Q Lang, an associate scientist in Geology
and Geophysics at the Woods Hole Oceanographic Institution, who was a co-chief
scientist on the expedition and part of a team continuing to analyse rock and
fluid samples, said: “The rocks that were present on early Earth bear a closer
resemblance to those we retrieved during this expedition than the more common
rocks that make up our continents today.
“Analysing them gives us a critical view into the
chemical and physical environments that would have been present early in
Earth’s history, and that could have provided a consistent source of fuel and
favorable conditions over geologically long timeframes to have hosted the earliest
forms of life.”
The international team of more than 30 scientists
from the JOIDES Resolution expedition will continue their research on the
recovered drill cores to address a wide range of problems.
Dr Andrew McCaig, an Associate Professor in the
School of Earth and Environment at the University of Leeds, who was the lead
proponent of Expedition 399 and a co-chief scientist on the Expedition added:
“Everyone involved in Expedition 399, starting with the first proposal in 2018,
can be proud of the achievements documented in this paper.
“Our new deep hole will be a type section for decades
to come in disciplines as diverse as melting processes in the mantle, chemical
exchange between rocks and the ocean, organic geochemistry and microbiology.
“All data from the expedition will be fully
available, an exemplar of how international science should be conducted.”
Their paper, ‘A long section of serpentinized
depleted mantle peridotite,’ is published in Science.
原始論文：C. Johan
Lissenberg, Andrew M. McCaig, Susan Q. Lang, Peter Blum, Natsue Abe, William J.
Brazelton, Rémi Coltat, Jeremy R. Deans, Kristin L. Dickerson, Marguerite
Godard, Barbara E. John, Frieder Klein, Rebecca Kuehn, Kuan-Yu Lin, Haiyang
Liu, Ethan L. Lopes, Toshio Nozaka, Andrew J. Parsons, Vamdev Pathak, Mark K.
Reagan, Jordyn A. Robare, Ivan P. Savov, Esther M. Schwarzenbach, Olivier J.
Sissmann, Gordon Southam, Fengping Wang, C. Geoffrey Wheat, Lesley Anderson,
Sarah Treadwell. A long section of serpentinized depleted mantle
peridotite. Science, 2024; 385 (6709): 623 DOI: 10.1126/science.adp1058
引用至：Woods
Hole Oceanographic Institution. "Record-breaking recovery of rocks that
originated in Earth's mantle could reveal secrets of planet's history."
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