在幼年地球上繁榮發展的生命：科學家發現年代為37億年的化石

原始網址：www.sciencedaily.com/releases/2016/08/160831172441.htm

在幼年地球上繁榮發展的生命：科學家發現年代為37億年的化石

在這項驚人的發現當中，來自澳洲的研究團隊在格陵蘭的偏遠地區發現了地球最古老的化石。這讓我們得知地球最久遠之前的歷史片段，顯示地球尚處年幼時生命便已經迅速出現在這顆星球上。

由澳洲臥龍崗大學的教授 Allen Nutman主持的研究團隊，在全世界最古老的沉積岩中發現了年代為37億年的疊層石(stromatolite)化石。此沉積岩分佈於格陵蘭冰蓋邊緣的Isua綠岩帶中。

刊登於期刊《自然》(Nature)上的論文中大略描述了這項發現，共同作者包括了澳洲國立大學的副教授Vickie Bennett、新南威爾斯大學的教授 Martin Van Kranendonk以及臥龍崗大學的教授 Allan Chivas。

Isua疊層石化石的發現讓我們對地球早期生命的多樣化程度有更長足的了解，研究人員說這也有助於我們認識火星生命的樣貌。臥龍崗大學地球與環境科學院的教授 Nutman說， 相較於之前發現於澳洲西部的最古老疊層石化石，Isua疊層石化石的年代還要早了2.2億年。

這項發現把化石紀錄出現的時間點回推至地球地質紀錄的原點附近，表示在地球歷史相當初期時就已經有生命跡象出現在地球上。 Isua疊層石位於長期積雪區近期因融化而露出的地帶。由於它們原先是在淺海地帶堆積而成，這成為了早期生命於何種環境繁榮生長的初步證據。

在地球歷史上很長一段時間，生命只不過是些單細胞生物。疊層石便是由這些微生物群落建構而成的碳酸鹽土丘。

「疊層石的重要之處不只是呈現出一種用肉眼就能見到的遠古生命證據，它還是一種複雜的生態系統。」Nutman教授說。

「這表示遠在37億年前微生物就已經發展出相當的多樣性了。發展出如此的生命多樣性顯示生命在地球誕生後的數億年內便已經出現了，這跟生物學家計算生物的基因編碼具有相當古老歷史的結果一致。」

共同研究人員，國立澳洲大學的副教授Vickie Bennett說這項研究給予了有關地球歷史的新觀點。

「這項發現徹底改變了對行星適居性的研究。」副教授Bennett 說。

「這是我們首度擁有維持早期生命的環境條件為何的岩石紀錄，而不僅只是臆測遠古環境的可能樣貌。我們的研究將會為幼年行星的化學循環和岩石-水-微生物之間的關係帶出最新觀點。」

新南威爾斯大學澳洲天體生物學中心(Nutman教授為準會員)的主任，Martin Van Kranendonk教授說這項突破性的發現指出37億年前火星的環境仍然濕潤時，其上也可能會有類似的生命結構。

「格陵蘭最新出露的露頭中含有的構造及地球化學性質特徵，在較年輕的岩石中皆可以用來指示其是否為生物來源。」 Van Kranendonk教授說。

「這項發現為地球生物留存下來的最古老證據設立了新的基準。它指出生命在地球上其實出現地相當迅速，也支持在火星上同樣古老的岩石中尋找生命是可行的。」

這項研究由澳洲科學團隊與英國研究人員合作來進行，並由澳洲國科會提供資金。

Life thrived on young Earth: scientists discover 3.7-billion-year-old fossils

In an extraordinary find, a team of Australian researchers have uncovered the world's oldest fossils in a remote area of Greenland, capturing the earliest history of the planet and demonstrating that life on Earth emerged rapidly in the planet's early years.

Led by the University of Wollongong's (UOW) Professor Allen Nutman, the team discovered 3.7-billion-year-old stromatolite fossils in the world's oldest sedimentary rocks, in the Isua Greenstone Belt along the edge of Greenland's icecap.

The findings are outlined in a study published in Nature, with co-authors Associate Professor Vickie Bennett from The Australian National University (ANU), the University of New South Wales' (UNSW) Professor Martin Van Kranendonk, and Professor Allan Chivas, from UOW.

The discovery of the Isua stromatolite fossils provides a greater understanding of early diversity of life on Earth and researchers said could have implications for our understanding of life on Mars. Professor Nutman, from UOW's School of Earth and Environmental Sciences, said the Isua stromatolite fossils predated the world's previous oldest stromatolite fossils -- which were found in Western Australia -- by 220 million years.

The discovery pushes back the fossil record to near the start of Earth's geological record and points to evidence of life on Earth very early in its history. The Isua stromatolites, which were exposed by the recent melting of a perennial snow patch, were laid down in shallow sea, providing the first evidence of an environment in which early life thrived.

For much of Earth's history, life was just single cells, and stromatolite fossils are mounds of carbonate constructed by these communities of microbes.

"The significance of stromatolites is that not only do they provide obvious evidence of ancient life that is visible with the naked eye, but that they are complex ecosystems," Professor Nutman said.

"This indicates that as long as 3.7 billion years ago microbial life was already diverse. This diversity shows that life emerged within the first few hundred millions years of Earth's existence, which is in keeping with biologists' calculations showing the great antiquity of life's genetic code."

Co-lead investigator Associate Professor Vickie Bennett, from ANU, said this study provided a new perspective into the history of Earth.

"This discovery turns the study of planetary habitability on its head," Associate Professor Bennett said.

"Rather than speculating about potential early environments, for the first time we have rocks that we know record the conditions and environments that sustained early life. Our research will provide new insights into chemical cycles and rock-water-microbe interactions on a young planet."

Professor Martin Van Kranendonk, Director of the Australian Centre for Astrobiology at UNSW, of which Professor Nutman is also an Associate Member, said it was a groundbreaking find that could point to similar life structures on Mars, which 3.7 billion years ago was a damp environment.

"The structures and geochemistry from newly exposed outcrops in Greenland display all of the features used in younger rocks to argue for a biological origin," Professor Van Kranendonk said.

"This discovery represents a new benchmark for the oldest preserved evidence of life on Earth. It points to a rapid emergence of life on Earth and supports the search for life in similarly ancient rocks on Mars."

The investigation, conducted by the Australian science team in collaboration with a UK partner, was funded by a grant from the Australian Research Council.

引用自：University of Wollongong. "Life thrived on young Earth: scientists discover 3.7-billion-year-old fossils: Remarkable find by team of Australian researchers points to earliest existence of diverse life on Earth." ScienceDaily. ScienceDaily, 31 August 2016. 

原始論文：Allen P. Nutman, Vickie C. Bennett, Clark R. L. Friend, Martin J. Van Kranendonk, Allan R. Chivas. Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature, 2016; DOI:10.1038/nature19355