Scientists Say Canadian Bacteria Fossils Are Earth’s Oldest
They are microscopic artwork: tiny tubes and long filaments, strange squiggles etched into some of the most ancient rocks known.
On Wednesday, researchers reported that these may be the oldest fossils ever discovered, the remains of bacteria thriving on Earth not long, geologically speaking, after the very birth of the planet. If so, they offer evidence that life here got off to a very early start.
But many experts in the field were skeptical of the new study — or downright unconvinced.
Martin J. Van Kranendonk, a geologist at the University of New South Wales, called the patterns in the rocks “dubiofossils” — fossil-like structures, perhaps, but without clear proof that they started out as something alive.
新南威尔士大学(University of New South Wales)的地质学专家马丁·J·范克拉嫩东克(Martin J. Van Kranendonk)称，那些岩石中的图案为“可疑化石”，即或许是类似化石的结构，但没有确凿的证据证明它们起初是有生命的东西。
Heated disputes are nothing new in the search for the earliest life on Earth.
In 1993 J. William Schopf, a paleontologist at the University of California, Los Angeles, and his colleagues found what that they, too, argued were the world’s oldest fossils: chainlike blobs in 3.46 billion-year-old rocks made, they said, by bacteria. Other researchers later argued that the structures were just oddly shaped minerals.
1993年，加州大学洛杉矶分校(University of California-Los Angeles)的古生物学家J·威廉·舍普夫(J. William Schopf)和同事在有34.6亿年历史的岩石中发现了链状斑纹。他们也宣称那是世界上最古老的化石，还说是细菌留下的。后来，其他一些研究人员认为，那些结构不过是形状奇怪的矿物质而已。
But additional specimens from other sites came to light over the past two decades, and many of them have withstood scrutiny. There is now solid evidence of life dating back about 3.5 billion years.
Earth was a billion years old by then, and scientists have long wondered if even older fossils might be found.
In August, Dr. Van Kranendonk and his colleagues reported discovering fossils in Greenland dating back 3.7 billion years. The scientists argued that the organisms were once mats of bacteria that grew in shallow coastal waters.
In the new study, published in the journal Nature, Mattew S.Dodd, Dominic Papineau and their colleagues at University College London studied rocks that were either slightly older or much older than those containing the Greenland fossils.
在成果已被《自然》(Nature)期刊发表的新研究中，马修·S·多德(Mattew S.Dodd)、多米尼克·帕皮诺(Dominic Papineau)及其伦敦大学学院(University College London)的同事对一些岩石做了研究，比起蕴含格陵兰化石的那些岩石，它们的年代或是稍稍久远一点，或是久远得多。
They came from a remote geological formation in Canada called Nuvvuagittuq, which stretches across four square miles on the coast of Hudson Bay. Geologists surveyed the formation for the first time in the 1990s.
Researchers have variously estimated its age at 3.77 billion years or 4.22 billion years — just 340 million years after the formation of the planet.
In 2008, Dr. Papineau collected rocks from the formation and found a number of clues indicating that they had formed around hydrothermal vents on the ancient sea floor that spewed iron and other minerals.
He also found hints that there might have been life there — tiny blobs of rock, for instance, that contained a compound called apatite, which can form from phosphorus released by dying organisms.
The tubes and other structures in the rock that Mr. Dodd found are also reminiscent of bacteria that live today around hydrothermal vents. They grow as filaments, feeding on iron compounds and creating tube-shaped cavities in the sediment.
Similar filaments contain iron compounds in the Nuvvuagittuq rocks, Mr. Dodd and his colleagues found, and they are attached to round clumps that resemble the tiny anchors bacteria use to hold onto rock surfaces. The rocks also contain forms of organic carbon that could have been created by bacteria.
The researchers argue that it would be unlikely for all of these features to have formed in the absence of life. “Then you’re left with one scenario — a biological origin,” Mr. Dodd said.
Such a discovery could have big implications for the understanding of life’s early evolution.
If these really are fossils 3.77 billion years old, then they show that life was already diversifying by that time, thriving in both the shallow ocean in what is now Greenland and the deep ocean in today’s Canada.
And if these are fossils 4.2 billion years old, then scientists will have evidence that life began quickly on Earth, not long after the oceans formed.
Yet Frances Westall, the director of research at the CNRS-Centre de Biophysique Moléculaire in Orléans, France, isn’t convinced these are fossils at all.
不过，法国奥尔良分子生物物理研究中心(CNRS-Centre de Biophysique Moléculaire)的研究主管弗朗西丝·韦斯托尔(Frances Westall)不太相信它们是化石。
“I am frankly dubious,” she said.
For one thing, she has argued, the filaments in the Nuvvuagittuq rocks are too big. She and her colleagues have found filaments formed by bacteria in rock dating back 3.3 billion years, and these are far smaller.
On the early Earth, bacteria were forced to stay small, Dr. Westall said, because the atmosphere did not yet have enough oxygen to fuel their growth.
Long after the Nuvvuagittuq rocks formed on the sea floor, they were heated to tremendous temperatures. Some experts doubted that microscopic fossils could have survived such a baking.
“These authors built their research on pushing speculative ideas and appear totally unaware of the considerable evidence against their interpretation,” said Wouter Bleeker, of the Geological Survey of Canada.
“这些论文作者把他们的研究建立在推测性理念之上，似乎完全没注意到与其解释相悖的大量证据，”加拿大地质调查局(Geological Survey of Canada)的沃特·布勒克尔(Wouter Bleeker)说。
In response, Dr. Papineau observed that the type of rock studied, known as chert, is very hard and might have protected fossils from high temperatures.
“I think the authors have done a good job,” said David Wacey, who researches the origins and evolution of life at the University of Western Australia. With the new evidence, he said, “One comes up with a pretty convincing biological scenario” for the origins of the mysterious rock features.
“我认为论文作者们做得不错，”在西澳大学(University of Western Australia)研究生命起源和进化问题的大卫·韦西(David Wacey)说。他说，有了这些新证据，就可以针对这些不可思议的岩石特征的起源“给出相当令人信服的生物学情境”。
Dr. Wacey was not surprised that the new work had drawn criticism.
“It may be many years before a consensus is reached,” he said. “But this is how science progresses.”