地球在41億年前就已經有生命出現，較科學家之前認為的還要早了許多

原文網址：www.sciencedaily.com/releases/2015/10/151019154153.htm

Life on Earth likely started 4.1 billion years ago, much earlier than scientists thought

地球在41億年前就已經有生命出現，較科學家之前認為的還要早了許多

Evidence that early Earth was not dry and desolate

證據顯示早期地球並非乾燥的不毛之地

UCLA geochemists have found evidence that life likely existed on Earth at least 4.1 billion years ago -- 300 million years earlier than previous research suggested. The discovery indicates that life may have begun shortly after the planet formed 4.54 billion years ago.

加州大學洛杉磯分校的地球化學家發現的證據，顯示生命很可能早在41億年前便已經存在於地球，比前人研究認為的還要早了3億年。此發現象徵著45.4億年前，地球形成不久後生命就誕生了。

The research is published today in the online early edition of the journal Proceedings of the National Academy of Sciences.

這篇研究今日(2015.10.19)發表在線上的《美國國家科學院學報》早版(early edition of Proceedings of the National Academy of Sciences)。

"Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking," said Mark Harrison, co-author of the research and a professor of geochemistry at UCLA.

「如果是在20年前，這番言論也許會被斥為一派胡言。發現38億年前已有生命存活的證據確實相當令人震驚。」此研究的共同作者，加州大學洛杉磯分校的地球化學教授Mark Harrison說。

"Life on Earth may have started almost instantaneously," added Harrison, a member of the National Academy of Sciences. "With the right ingredients, life seems to form very quickly."

「生命可能與地球幾乎同時形成。」Harrison補充說，他也是一名美國國家科學院院士。「有了適當的原料，生命似乎很快便能從中誕生。」

The new research suggests that life existed prior to the massive bombardment of the inner solar system that formed the moon's large craters 3.9 billion years ago.

這項新研究認為生命在39億年前，形成月球眾多巨型隕石坑的內太陽系大轟炸事件之前就已存在。

"If all life on Earth died during this bombardment, which some scientists have argued, then life must have restarted quickly," said Patrick Boehnke, a co-author of the research and a graduate student in Harrison's laboratory.

「正如一些科學家提出的說法，若地球上所有生命都在大轟炸事件中死亡，那麼生命必然很快又東山再起。」共同作者，Harrison研究室的研究生Patrick Boehnke說。

Scientists had long believed the Earth was dry and desolate during that time period. Harrison's research -- including a 2008 study in Nature he co-authored with Craig Manning, a professor of geology and geochemistry at UCLA, and former UCLA graduate student Michelle Hopkins -- is proving otherwise.

科學家長久以來認為在那段時期，地球是一片乾旱的荒蕪之地。Harrison的研究，包括他在2008年與Craig Manning和Michelle Hopkins刊登於《自然》的共同著作，卻證明事實並非如此。Craig Manning 為加州大學洛杉磯分校的地質和地球化學教授；Michelle Hopkins則是之前就讀於同所大學的研究生。

"The early Earth certainly wasn't a hellish, dry, boiling planet; we see absolutely no evidence for that," Harrison said. "The planet was probably much more like it is today than previously thought."

「地球早年絕非是一座乾燥且熾熱的煉獄，我們並未看到任何證據可以支持此說法。」Harrison說。「也許在當時，這顆星球比我們先前認為的還要與目前更加相似。」

The researchers, led by Elizabeth Bell -- a postdoctoral scholar in Harrison's laboratory -- studied more than 10,000 zircons originally formed from molten rocks, or magmas, from Western Australia. Zircons are heavy, durable minerals related to the synthetic cubic zirconium used for imitation diamonds. They capture and preserve their immediate environment, meaning they can serve as time capsules.

此篇研究由Harrison實驗室的特約博士後研究員Elizabeth Bell領導。他們研究了產自澳洲西部，形成於熔化岩石，即岩漿中的一萬多顆鋯石(zircon)碎屑。鋯石是一種高密度且相當堅硬的礦物，與用來製作人造鑽石的人造立方氧化鋯相當類似。它們可以捕捉並且保存形成當時的環境資訊，意味著它們就像時光膠囊一般。

The scientists identified 656 zircons containing dark specks that could be revealing and closely analyzed 79 of them with Raman spectroscopy, a technique that shows the molecular and chemical structure of ancient microorganisms in three dimensions.

科學家發現其中的656顆鋯石碎屑含有暗色微粒，在這之中有79顆鋯石的微粒可以用拉曼光譜(Raman spectroscopy)來檢視並詳細分析。拉曼光譜是一種可以檢視古代微生物的分子和化學三維構造的技術。

Bell and Boehnke, who have pioneered chemical and mineralogical tests to determine the condition of ancient zircons, were searching for carbon, the key component for life.

Bell和Boehnke率先使用化學和礦物試驗來確認這些遠古鋯石形成時的環境，它們的目標是尋找形成生物的關鍵成分--碳。

One of the 79 zircons contained graphite -- pure carbon -- in two locations.

在79顆鋯石中，有一顆鋯石內的兩處有石墨分佈，這是一種純碳。

"The first time that the graphite ever got exposed in the last 4.1 billion years is when Beth Ann and Patrick made the measurements this year," Harrison said.

「今年Beth Ann與Patrick進行測量時，首度發現在41億年前石墨就已經出現了。」Harrison說。

How confident are they that their zircon represents 4.1 billion-year-old graphite?

他們對他們的鋯石真的含有形成於41億年前的石墨有多少信心？

"Very confident," Harrison said. "There is no better case of a primary inclusion in a mineral ever documented, and nobody has offered a plausible alternative explanation for graphite of non-biological origin into a zircon."

「我們相當有信心。」Harrison說。「有關礦物原始包裹體(primary inclusion)的文獻中沒有比這更佳的案例，而且也沒有人提出其他可信說法能解釋鋯石裡的石墨其實是非生物來源。」

The graphite is older than the zircon containing it, the researchers said. They know the zircon is 4.1 billion years old, based on its ratio of uranium to lead; they don't know how much older the graphite is.

研究人員說石墨比包覆它的鋯石還要古老。藉由測量鋯石中鈾跟鉛的比例，他們得知鋯石的年代為41億年，但他們並無法確知石墨究竟有多老。

The research suggests life in the universe could be abundant, Harrison said. On Earth, simple life appears to have formed quickly, but it likely took many millions of years for very simple life to evolve the ability to photosynthesize.

Harrison說此研究顯示了生命可能存活在宇宙各處。地球上簡單生命可能出現得相當迅速，然而，生命要從十分簡當演化成能夠行使光合作用，可能得耗費數百萬年的時間。

The carbon contained in the zircon has a characteristic signature -- a specific ratio of carbon-12 to carbon-13 -- that indicates the presence of photosynthetic life.

鋯石裡的碳其碳-12與碳-13之間具有獨特比例，而這種特殊訊號指示出能進行光合作用的生命已然出現。

"We need to think differently about the early Earth," Bell said.

「我們需要以不同的眼光看待早期地球。」Bell說。

Wendy Mao, an associate professor of geological sciences and photon science at Stanford University, is the other co-author of the research.

此研究的另一位共同作者Wendy Mao是史丹佛大學地質科學與光子科學系的副教授。

The research was funded by the National Science Foundation and a Simons Collaboration on the Origin of Life Postdoctoral Fellowship granted to Bell.

Bell的這項博士後研究由西蒙斯基金會的生命起源合作計畫授予，並由國家科學基金會資助。

引用自：University of California - Los Angeles. "Life on Earth likely started 4.1 billion years ago, much earlier than scientists thought: Evidence that early Earth was not dry and desolate." ScienceDaily. ScienceDaily, 19 October 2015.