微生物誕生所需的條件在35億年前就已經存在於我們的星球。一組國際團隊從澳洲馬布爾巴的德雷瑟礦坑取出硫酸鋇(重晶石)，研究裡面的微小液包體後得出了這項結論。在他們發表於期刊《自然通訊》(Nature Communications)的文章「35億年前的液包體保存了微生物形成的原料」當中，研究人員提出可以作為微生物養分的有機碳化合物在當時就已經存在。論文第一作者為德國哥廷根大學的Helge Mißbach，而德國地球科學研究中心(GFZ)的Volker Lüders也參與其中，他於有機地球化學部門分析了液包體中氣體的碳同位素。
這些富含氣體的液包體中帶有二氧化碳和甲烷，它們是在宿主礦物(此處為石英)的晶體成長過程當中被包進來的。圖片來源：Volker Lüders
液包體顯示了史前生命的可能跡象
Lüders雖然預計結果會讓人感到驚訝，但也慎重表示不要有所曲解。「不能把這份研究看作是早期生命的直接證據，」這位GFZ的研究人員表示。更準確地來說，從這些35億年前的液體中得到的發現，顯示的只是這類史前生命存在的可能性，但無法確定當時是否真的有生命從中誕生。根據這項結果，「我們現在知道的是，有個時間點可以讓我們說這在當時可能發生了這件事，」Lüders解釋。
保存在地質中的文獻：澳洲的重晶石
研究團隊分析了澳洲重晶石裡的液包體，藉此得知它們形成時的環境條件(壓力、溫度、溶液成分)、生物訊號與碳同位素。礦物中的液包體就像一種微型的地質文獻，保存了從地殼裡遷移進來的高溫液體和氣體。原生液包體是在礦物生長的過程當中直接被包進來，因此可以提供礦物形成環境的重要資訊。除了液體之外，包裹體裡面可能也會有氣體，其化學性質可以保存數十億年之久。這篇研究中檢視的液包體是在宿主礦物的結晶過程中包進來的，隨著分析進行，也逐漸得出它們含有原始的代謝反應，因此具有生命的能量來源。Lüders的碳同位素分析結果也證實了碳來自於不同的地方。雖然灰色重晶石裡面富含氣體的包裹體，含有來自岩漿的碳留下的痕跡，但在黑色重晶石裡面的液包體，卻有清楚的證據顯示碳也來自有機物。
未來也許會有研究跟進
「這項研究可能會激起很大的波瀾，」Lüders表示。在此之前，這種類型的有機分子還沒在太古宙礦物裡的液包體找到過，但同時他也認為這項研究只是個開始。Lüders說：「隨著測量儀器的靈敏度不斷提升，科學家未來勢必能擁有新的工具來研究礦物中微小的液體與氣體包裹體。在不久的將來，生物訊號與同位素比例的測量結果有可能會變得越來越精準。」
Preconditions for life already 3.5
billion years ago
Microbial life already had the necessary
conditions to exist on our planet 3.5 billion years ago. This was the conclusion
reached by a research team after studying microscopic fluid inclusions in
barium sulfate (barite) from the Dresser Mine in Marble Bar, Australia. In
their publication "Ingredients for microbial life preserved in
3.5-billion-year-old fluid inclusions," the researchers suggest that
organic carbon compounds that could serve as nutrients for microbial life
already existed at this time. Volker Lüders from the GFZ German Research Center
for Geosciences was also involved in the study by first author Helge Mißbach
(University of Göttingen, Germany), which was published in the journal Nature Communications. Lüders carried
out carbon isotope analyses on gases in fluid inclusions in the Organic
Geochemistry Section.
Fluid inclusions
show potential for prehistoric life
Lüders assesses the results as surprising, although
he cautions against misinterpreting them. "One should not take the study
results as direct evidence for early life," says the GFZ researcher.
Rather, the findings on the 3.5-billion-year-old fluids showed the existence of
the potential for just such prehistoric life. Whether life actually arose from
it at that time cannot be determined. Based on the results, “we now know a
point in time from which we can say it would have been possible," explains
Lüders.
Australian
barites as geo-archives
The research team has analyzed fluid inclusions in
Australian barites for formation conditions (pressure, temperature and solution
composition), bio signatures, and carbon isotopes. Fluid inclusions in minerals
are microscopic geo-archives for the migration of hot solutions and gases in
the Earth’s crust. Primary fluid inclusions were formed directly during mineral
growth and provide important information about the conditions under which they
were formed. In addition to an aqueous phase, fluid inclusions can also contain
gases whose chemistry can persist for billions of years. The fluid inclusions
examined in this study were trapped during crystallization of the host
minerals. In the course of the analyses, it turned out that they contained
primordial metabolism - and thus energy sources for life. The results of
Lüders' carbon isotope analysis provided additional evidence for different
carbon sources. While the gas-rich inclusions of gray barites contained traces
of magmatic carbon, clear evidence of an organic origin of the carbon could be
found in the fluid inclusions of black barites.
Follow-up
research is possible
"The study may create a big stir," Lüders
says. Organic molecules of this type have not yet been found so far in fluid
inclusions in Archean minerals. At the same time, however, he says the study is
just a first step. Lüders says, "The ever-increasing sensitivity of
measuring instruments will provide new tools for the study of solid and fluid
micro inclusions in minerals. Measurements of bio signatures and isotope ratios
are likely to become increasingly accurate in the near future."
原始論文：Helge Mißbach,
Jan-Peter Duda, Alfons M. van den Kerkhof, Volker Lüders, Andreas Pack, Joachim
Reitner, Volker Thiel. Ingredients for microbial life preserved in 3.5
billion-year-old fluid inclusions. Nature Communications, 2021;
12 (1) DOI: 10.1038/s41467-021-21323-z
引用自：GFZ GeoForschungsZentrum Potsdam, Helmholtz
Centre. "Preconditions for life present 3.5 billion years ago."
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