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This sample of rock was taken from the Apex Chert, a rock formation in western Australia that is among the oldest and best-preserved rock deposits in the world, in 1982 and was soon found to contain evidence of early life on Earth. A study published by UCLA and UW-Madison scientists in 2017 used sophisticated chemical analysis to confirm the microscopic structures found in the rock are indeed biological, rendering them -- at 3.5 billion years -- the oldest fossils yet found. This is the rock after analysis in the WiscSIMS Laboratory. Credit: John Valley, UW-Madison

这个岩石样品是从1982年在澳大利亚西部的一个岩层Apex Chert取得的,这个岩层是世界上最古老,保存最完好的岩石矿床之一,很快就发现它含有地球早期生命的证据。加利福尼亚大学洛杉矶分校和威斯康星大学麦迪逊分校的科学家们在2017年发表的一项研究使用了先进的化学分析手段,以确认在岩石中发现的微观结构确实是生物学的,使得它们在35亿年前是最古老的化石。这是在WiscSIMS实验室分析后的岩石。

Researchers at UCLA and the University of Wisconsin-Madison have confirmed that microscopic fossils discovered in a nearly 3.5 billion-year-old piece of rock in Western Australia are the oldest fossils ever found and indeed the earliest direct evidence of life on Earth.

加州大学洛杉矶分校和威斯康辛大学麦迪逊分校的研究人员证实,在澳大利亚西部一块近35亿年历史的一块岩石中发现的化石,是迄今为止发现的最古老的化石,也是地球上最早的生命存在的证据。

The study, published today in the Proceedings of the National Academy of Sciences, was led by J. William Schopf, professor of paleobiology at UCLA, and John W. Valley, professor of geoscience at the University of Wisconsin-Madison. The research relied on new technology and scientific expertise developed by researchers in the UW-Madison WiscSIMS Laboratory.

这项研究发表在《美国国家科学院院刊》(Proceedings of The National Academy of Sciences)上。该研究由美国加州大学洛杉矶分校的古生物学教授j·威廉·施普夫(j . William Schopf)和威斯康辛大学麦迪逊分校(University of wisconsin - madison)的地球科学教授约翰·w·谷(John w . Valley)领导。这项研究依赖于uw - madison WiscSIMS实验室的研究人员开发的新技术和科学技术。

The study describes 11 microbial specimens from five separate taxa, linking their morphologies to chemical signatures that are characteristic of life. Some represent now-extinct bacteria and microbes from a domain of life called Archaea, while others are similar to microbial species still found today. The findings also suggest how each may have survived on an oxygen-free planet.

这项研究描述了来自五个不同分类单元的11个微生物样本,将它们的形态与生命特征的化学特征联系起来。一些代表了现在已经灭绝的细菌和微生物,这些细菌和微生物来自一种叫做古菌(Archaea)的生物领域,而另一些则类似于今天仍然存在的微生物。这些发现还表明,它们如何在无氧的星球上幸存下来。

The microfossils—so called because they are not evident to the naked eye—were first described in the journal Science in 1993 by Schopf and his team, which identified them based largely on the fossils' unique, cylindrical and filamentous shapes. Schopf, director of UCLA's Center for the Study of Evolution and the Origin of Life, published further supporting evidence of their biological identities in 2002.

所谓的微化石,因为它们不是肉眼可见的 - 在Schopf和他的团队1993年的“科学”(Science)杂志中首次描述,他们在很大程度上根据化石的独特,圆柱形和丝状形状来确定它们。加州大学洛杉矶分校进化与生命起源研究中心主任Schopf在2002年发表了进一步支持他们生物身份的证据。

He collected the rock in which the fossils were found in 1982 from the Apex chert deposit of Western Australia, one of the few places on the planet where geological evidence of early Earth has been preserved, largely because it has not been subjected to geological processes that would have altered it, like burial and extreme heating due to plate-tectonic activity.

他在1982年从西澳大利亚州埃佩克斯硅质岩矿藏中收集了发现化石的岩石,这是地球上为数不多的保存早期地质地质证据的地方之一,这在很大程度上是因为它没有受到地质作用会改变它,比如由于板块构造活动而造成的埋藏和极端加热。

But Schopf's earlier interpretations have been disputed. Critics argued they are just odd minerals that only look like biological specimens. However, Valley says, the new findings put these doubts to rest; the microfossils are indeed biological.

但是Schopf早先的解释有争议。批评者认为,他们只是奇怪的矿物,只是看起来像生物标本。然而,谷说,新的发现使这些疑虑得以停止。微化石确实是生物的。

"I think it's settled," he says.

他说:“我认为这已经解决了。

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An example of one of the microfossils discovered in a sample of rock recovered from the Apex Chert, a rock formation in western Australia that is among the oldest and best-preserved rock deposits in the world. The fossils were first described in 1993 but a 2017 study published by UCLA and UW-Madison scientists used sophisticated chemical analysis to confirm the microscopic structures found in the rock are indeed biological, rendering them -- at 3.5 billion years -- the oldest fossils yet found. Credit: J. William Schopf, UCLA

这是一个在岩石样本中发现的一个微化石的例子,它是在澳大利亚西部的一个岩层中发现的,它是世界上最古老、保存最完好的岩石之一。这些化石最初是在1993年探索的,但是由加利福尼亚大学洛杉矶分校和威斯康星大学麦迪逊分校出版的2017年的一项研究使用了复杂的化学分析,以确认在岩石中发现的微观结构确实是生物学的,使它们在35亿年前是最古老的化石找到。

Using a secondary ion mass spectrometer (SIMS) at UW-Madison called IMS 1280—one of just a handful of such instruments in the world—Valley and his team, including department geoscientists Kouki Kitajima and Michael Spicuzza, were able to separate the carbon composing each fossil into its constituent isotopes and measure their ratios.

在威斯康星大学麦迪逊分校使用二次离子质谱仪(SIMS),名为IMS1280-世界上只有少数这种仪器之一的Valley和他的团队,包括地球科学家Kouki Kitajima和Michael Spicuzza,能够分离碳排放每个化石都归入其组成同位素,并衡量其比例。

Isotopes are different versions of the same chemical element that vary in their masses. Different organic substances—whether in rock, microbe or animal—contain characteristic ratios of their stable carbon isotopes.

同位素是相同化学元素的不同版本,其质量各不相同。不同的有机物质,无论是岩石,微生物还是动物,都含有稳定碳同位素的特征比例。

Using SIMS, Valley's team was able to tease apart the carbon-12 from the carbon-13 within each fossil and measure the ratio of the two compared to a known carbon isotope standard and a fossil-less section of the rock in which they were found.

使用SIMS,Valley的研究小组能够从每个化石中的碳-13中分离出碳-12,并测量两者的比例,与已知的碳同位素标准和发现它们的岩石的无化石部分。

"The differences in carbon isotope ratios correlate with their shapes," Valley says. "If they're not biological there is no reason for such a correlation. Their C-13-to-C-12 ratios are characteristic of biology and metabolic function."

“碳同位素比率的差异与其形状有关,”Valley说。“如果它们不是生物的话,就没有理由有这样的相关性,它们的C-13-C-12比例是生物学和代谢功能的特征。

Based on this information, the researchers were also able to assign identities and likely physiological behaviors to the fossils locked inside the rock, Valley says. The results show that "these are a primitive, but diverse group of organisms," says Schopf.

根据这些信息,研究人员还能够将身份和可能的生理行为分配到岩石内部的化石中,Valley说。结果表明,“这些是一个原始的,但不同的生物群体,”Schopf说。

The team identified a complex group of microbes: phototrophic bacteria that would have relied on the sun to produce energy, Archaea that produced methane, and gammaproteobacteria that consumed methane, a gas believed to be an important constituent of Earth's early atmosphere before oxygen was present.

该小组确定了一组复杂的微生物:依赖太阳产生能量的光养细菌,产生甲烷的古细菌,以及消耗甲烷的γ-蛋白质细菌,这种气体被认为是氧气存在之前地球早期大气层的重要组成部分。

It took Valley's team nearly 10 years to develop the processes to accurately analyze the microfossils—fossils this old and rare have never been subjected to SIMS analysis before. The study builds on earlier achievements at WiscSIMS to modify the SIMS instrument, to develop protocols for sample preparation and analysis, and to calibrate necessary standards to match as closely as possible the hydrocarbon content to the samples of interest.

他们花了将近10年的时间来开发这个过程,以准确地分析这些古老而稀有的化石以前从未受过SIMS分析的微化石。该研究建立在WiscSIMS的早期成果之上,用于修改SIMS仪器,制定样品制备和分析方案,并校准必要的标准,以尽可能地使碳氢化合物含量与感兴趣的样品相匹配。

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The Apex Chert, a rock formation in western Australia that is among the oldest and best-preserved rock deposits in the world. In 1982, at the site pictured here, a team of geologists sampled rock that was ultimately found to contain microfossils of the oldest life yet described on Earth. Pictured are UW-Madison geoscience researchers on a field trip to the site in 2010. Credit: John Valley, UW-Madison

Apex Chert是澳大利亚西部的一个岩层,是世界上历史最悠久,保存最完好的岩石之一。1982年,在图片所在的地方,一组地质学家对岩石进行了采样,最终发现岩石含有地球上描述的最古老生物的微化石。图为美国威斯康星大学地球科学研究人员在2010年的实地考察。

In preparation for SIMS analysis, the team needed to painstakingly grind the original sample down as slowly as possible to expose the delicate fossils themselves—all suspended at different levels within the rock and encased in a hard layer of quartz—without actually destroying them. Spicuzza describes making countless trips up and down the stairs in the department as geoscience technician Brian Hess ground and polished each microfossil in the sample, one micrometer at a time.

在准备进行SIMS分析时,团队需要尽可能慢地磨碎原始样本,以便将自身的微妙化石暴露在岩石的不同层面,并将其封装在石英的坚硬层中,而不会实际破坏它们。Spicuzza描述了在地球科学技术人员Brian Hess研磨并在样品中磨光每一个微化石,每次一微米的时候,在这个部门的楼梯上下无数的行程。

Each microfossil is about 10 micrometers wide; eight of them could fit along the width of a human hair.

每个微化石约10微米宽; 其中8个可以与人类头发的宽度相匹配。

Valley and Schopf are part of the Wisconsin Astrobiology Research Consortium, funded by the NASA Astrobiology Institute, which exists to study and understand the origins, the future and the nature of life on Earth and throughout the universe.

Valley和Schopf是由美国宇航局天体生物学研究所资助的威斯康星天体生物学研究联盟的一部分,该研究所旨在研究和理解地球上和整个宇宙的起源,未来和生命的本质。

Studies such as this one, Schopf says, indicate life could be common throughout the universe. But importantly, here on Earth, because several different types of microbes were shown to be already present by 3.5 billion years ago, it tells us that "life had to have begun substantially earlier—nobody knows how much earlier—and confirms it is not difficult for primitive life to form and to evolve into more advanced microorganisms," says Schopf.

Schopf说,像这样的研究表明,宇宙中的生命可能是共同的。但重要的是,在地球上,由于几十五亿年前已经有几种不同类型的微生物出现,它告诉我们“生命早就开始了 - 人们早就知道了多少 - 并证实这并不困难为原始生命形成并演变成更先进的微生物,“Schopf说。

Earlier studies by Valley and his team, dating to 2001, have shown that liquid water oceans existed on Earth as early as 4.3 billion years ago, more than 800 million years before the fossils of the present study would have been alive, and just 250 million years after the Earth formed.

Valley和他的研究小组早期的研究表明,早在43亿年前,地球上就有液态水存在,距离本研究的化石还有8亿年以上的历史,还有2.5亿年几年后,地球形成。

"We have no direct evidence that life existed 4.3 billion years ago but there is no reason why it couldn't have," says Valley. "This is something we all would like to find out."

Valley说:“我们没有直接的证据证明生命存在了43亿年前,但没有理由不存在。“这是我们都希望找到的东西。”

UW-Madison has a legacy of pushing back the accepted dates of early life on Earth. In 1953, the late Stanley Tyler, a geologist at the university who passed away in 1963 at the age of 57, was the first person to discover microfossils in Precambrian rocks. This pushed the origins of life back more than a billion years, from 540 million to 1.8 billion years ago.

威斯康星州麦迪逊有一个遗产,推迟了地球上早期生活的接受日期。1953年,已故大学的地质学家斯坦利·泰勒(Stanley Tyler)于1963年去世,享年57岁,是第一个在前寒武纪岩石中发现微化石的人。这将生命起源从五亿四千万年推到十八亿年前。

"People are really interested in when life on Earth first emerged," Valley says. "This study was 10 times more time-consuming and more difficult than I first imagined, but it came to fruition because of many dedicated people who have been excited about this since day one ... I think a lot more microfossil analyses will be made on samples of Earth and possibly from other planetary bodies."

Valley说:“人们真正对地球上的生命何时出现感兴趣。“这项研究耗时10倍,比我想象的要困难得多,但是由于许多敬业的人从第一天开始就对此感到兴奋,所以这项研究取得了成果......我认为还将进行更多的微化石分析对地球的样本和可能来自其他行星体的样本“。

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