Supplement to this post, The Oldest Rocks – The Pictures.
Classic rock, Record-setting 4-billion-year-old rocks uncovered in Northern Quebec
ANNE MCILROY
SCIENCE REPORTER, The Globe and Mail
September 26, 2008
The oldest rocks yet found in the world lie in a weathered stretch of bedrock in Northern Quebec, and the researchers who discovered them say they offer an unprecedented glimpse of what the young Earth was like.
The rocks are 4.28 billion years old and were found on the eastern shore of Hudson Bay during the past year. The Earth is 4.6 billion years old, so the rocks have been around since roughly 300 million years after the birth of the planet, said Jonathan O’Neil, a doctoral candidate at McGill University in Montreal and the lead author of a paper to be published in today’s edition of the journal Science.
Their chemical composition offers clues about the distant past and suggests that there was liquid water on the surface back then, and that temperatures and atmospheric pressure were similar to today.
“The Earth wasn’t a glacier and it wasn’t a steam ball,” said Richard Carlson, a geochemist at the Carnegie Institution in Washington and a member of a team that included Don Francis at McGill and Ross Stevenson at the University of Quebec in Montreal. The makeup of the rocks suggests that continents formed early, Dr. Carlson said. The ancient rocks resemble modern volcanic ones found in places where tectonic plates crash together, such as the Cascade mountain range that extends from southern British Columbia into the United States, or the Aleutian Islands in Alaska.
Previously, the oldest known rocks were from an outcrop known as Acasta Gneiss in the Northwest Territories, southeast of Great Bear Lake, which are four billion years old.
Tiny mineral grains within rocks in Western Australia have been dated at 4.36 billion years old. Each is about the size of a grain of sand.
“But what we have is the actual rock,” Mr. O’Neil said.
Water-soluble elements in the rocks are evidence that liquid water was present, Dr. Carlson says, and suggest that the Earth cooled from an extremely hot, molten state surprisingly quickly.
“It went from a totally molten state to something that isn’t dramatically different from today within 200 million years,” he said.
It is rare to find remnants of the early crust, he says, because most of it has been mashed and recycled into the Earth’s interior by plate tectonics.
A previous find in the same belt also added to what we know about early years on Earth. In 2001, geologists found a different type of rock in the same formation that was 3.8 billion years old.
Those rocks offered the first direct evidence that carbon dioxide – the culprit in modern, manmade global warming – might have stopped the young Earth from freezing over.
Astrophysicists believe the sun was 25 per cent fainter then, and many researchers had theorized that high concentrations of greenhouse gases helped the planet avoid global freezing. The 3.8-billion-year-old rocks contained compounds called iron carbonates, which could have been formed only if the atmosphere contained far more carbon dioxide that it does today.
Mr. O’Neil spent the last year looking at the relationships between the different types of rocks in the belt. He knew that some of the very old rocks were mixed in with much younger material.
He used a new technique for terrestrial rocks to determine that some bits of the belt were 4.28 billion years old.
Mr. O’Neil has fist-sized samples in his office. As word spreads that they are the oldest rocks in the world, he said, his colleagues have started coming by to touch them.
They are a remnant, he said, of a time when shallow seas may have lapped the shores of fledgling continents.
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Discovery of world’s oldest rocks challenged
11:28 26 September 2008
NewScientist.com news service
Catherine Brahic
A large band of ancient rocks in northern Quebec, known as the Nuvvuagittuq greenstone belt, has produced what may be the oldest rock on Earth – at 4.28 billion years old (Image: Science/AAAS)
Geologists in Canada may have discovered the oldest rocks on Earth. But a controversy over the techniques used to date the rocks is threatening to overshadow the discovery.
Finding the oldest rocks on Earth is important because they should help scientists solve one of geology’s great mysteries: how the surface of our planet was transformed from the ocean of magma that existed in the Hadean – the earliest era in Earth’s history – into the floating tectonic plates we have today.
For the last four years, Jonathan O’Neil of McGill University and colleagues have been studying a large band of ancient rocks in northern Quebec known as the Nuvvuagittuq greenstone belt. However, the team has used a controversial method for dating the rocks.
The dating method relies on the amount of the common isotope neodymium-142 in the rock. All rocks contain some neodymium-142, but rocks older than 4.2 billion years should contain more of it.
That’s because it is produced by the radioactive decay of samarium-146, which had largely disappeared 4.2 billion years ago. Any rocks that formed while samarium-146 was still around would today contain larger than usual quantities of neodymium-142.
“You can precisely measure the amount of neodymium-142 and calculate a precise age for the rock,” explains O’Neil. “In our case it gave us an age of 4.28 billion years.” That’s significantly older than any rock yet found on Earth.
Moon-forming blow
This could make the greenstone belt the oldest known rocks on Earth, just 300 million years younger than our solar system. It also dates them close to the time when a massive object the size of Mars dealt Earth a glancing blow 4.53 billion years ago, knocking off the debris which formed the Moon.
The energy of the blow was such that the Earth’s upper layers melted into an ocean of magma. The next period for which we have evidence in the evolution of Earth is around 3.8 billion years ago, by which time most geologists agree plate tectonics were in place.
“What we really want to get to is what Earth looked like before 4 billion years ago,” says Martin Whitehouse of the Swedish Museum of Natural History, who was not involved in the study.
“We want to understand how the early Earth transitioned from a magma ocean through to the Earth at 3.8 billion years. Somewhere in those 700 million years something changed. Any shred of evidence is important in trying to reconstruct this evolution.”
Ancient magma?
“To study how early crust formed we need to have samples of these rocks,” says O’Neil. With rocks in hand, it becomes possible to analyse every aspect of them and retrace their history. O’Neil’s latest find could help with that process.
However, the neodymium-142 levels may not be an indicator of the rock’s age. O’Neil himself admits his team may instead be measuring the age of the magma from which the rocks formed. “All rocks have precursor, something that came before they formed,” says Whitehouse.
O’Neil’s team has also used a conventional method to date the rocks which suggests the greenstone belt is only 3.8 billion years old – about 200 million years younger than the current oldest rock – Acasta gneiss, which was discovered in Canada in 1999.
It is clear that O’Neil and his colleagues have discovered one of the oldest signals from the very early stages in our planet’s development. But how the signal should be interpreted “is going to be very controversial”, says Whitehouse.
“On the weight of evidence from other studies in the area, I would still consider that 3.8 billion years is more likely the actual age of the rocks,” says Simon Wilde of the Institute for Geoscience Research in Australia.
Journal reference: Science (DOI: 10.1126/science.1161925)
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Canada home to world’s oldest rocks, researchers say
Friday, September 26, 2008 | 10:49 AM ET
CBC News
The Nuvvuagittuq belt region along the coast of Hudson’s Bay in Northern Quebec is the home of ancient rocks that may be as old as 4.28 billion years, according to a team of Canadian and U.S. researchers. (Science/AAAS)
Canadian and U.S. researchers say they have found the oldest rocks in the world, along the Northern Quebec coast of Hudson’s Bay.
The rocks, found in an area known as the Nuvvuagittuq greenstone belt about 40 kilometres south of Inukjuak, are estimated to be 4.28 billion years old, according to a team of researchers from McGill University, Université du Québec à Montréal (UQAM) and the Carnegie Institution for Science in Washington, D.C.
That would put the creation of the rocks at roughly 300 million years after the planet was formed, making them the oldest preserved piece of the Earth’s early crust, researchers said Thursday.
Jonathan O’Neil, a Ph.D. candidate at McGill’s department of Earth and planetary sciences and the lead author of a study to be published in Friday’s issue of the journal Science, said the discovery would offer new insight into the early Earth.
“Our discovery not only opens the door to further unlock the secrets of the Earth’s beginnings,” said O’Neil in a statement. “Geologists now have a new playground to explore how and when life began, what the atmosphere may have looked like, and when the first continent formed.”
The rocks are known as “faux-amphibolites,” taking their name from their resemblance to another class of rocks mostly composed of silica minerals. Unlike regular amphibolites, which are dark green or pitch black in appearance, rocks in this other class are beige or sugar brown, O’Neil told CBC News.
The researchers used isotopic dating, analyzing the decay of the radioactive elements neodymium-142 and samarium-146 to determine the age of the rocks. The technique is unique because of the instability of samarium-146. Although the isotope of the element was believed to have formed in the early Earth, remnants of it are extremely rare in all but the oldest rocks because it decays so quickly. That the researchers were able to find the isotope at all told them the rock was at least four billion years old, said O’Neil.
Finding remnants of the early Earth is extremely rare, said O’Neil. The oldest previously known rocks were found in an outcrop called the Acasta Gneiss, which lies southeast of Great Bear Lake in the northwestern corner of the Canadian Shield in the Northwest Territories.
Richard Carlson, a researcher at the Carnegie Institution for Science, Don Francis, a McGill professor in the department of Earth and planetary sciences, and UQAM professor Ross Stevenson were the paper’s other authors.
O’Neil said the next step is to look at the chemical composition of more samples from the same region in Northern Quebec.
“These rocks can give us clues as to how the first continents formed, but they may also tell us about atmospheric conditions and possibly the origins of life,” he said.
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Team finds Earth’s ‘oldest rocks’ |
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Earth’s most ancient rocks, with an age of 4.28 billion years, have been found on the shore of Hudson Bay, Canada. Writing in Science journal, a team reports finding that a sample of Nuvvuagittuq greenstone is 250 million years older than any rocks known. It may even hold evidence of activity by ancient life forms. If so, it would be the earliest evidence of life on Earth – but co-author Don Francis cautioned that this had not been established. “The rocks contain a very special chemical signature – one that can only be found in rocks which are very, very old,” he said. The professor of geology, who is based at McGill University in Montreal, added: “Nobody has found that signal any place else on the Earth.” “Originally, we thought the rocks were maybe 3.8 billion years old.
“Now we have pushed the Earth’s crust back by hundreds of millions of years. That’s why everyone is so excited.” Ancient rocks act as a time capsule – offering chemical clues to help geologists solve longstanding riddles of how the Earth formed and how life arose on it. But the majority of our planet’s early crust has already been mashed and recycled into Earth’s interior several times over by plate tectonics. Before this study, the oldest whole rocks were from a 4.03 billion-year-old body known as the Acasta Gneiss, in Canada’s Northwest Territories. The only things known to be older are mineral grains called zircons from Western Australia, which date back 4.36 billion years. Date range Professor Francis was looking for clues to the nature of the Earth’s mantle 3.8 billion years ago. He and colleague Jonathan O’Neil, from McGill University, travelled to remote tundra on the eastern shore of Hudson Bay, in northern Quebec, to examine an outcrop of the Nuvvuagittuq greenstone belt. They sent samples for chemical analysis to scientists at the Carnegie Institution of Washington, who dated the rocks by measuring isotopes of the rare earth elements neodymium and samarium, which decay over time at a known rate. The oldest rocks, termed “faux amphibolite”, were dated within the range from 3.8 to 4.28 billion years old. “4.28 billion is the figure I favour,” says Francis. “It could be that the rock was formed 4.3 billion years ago, but then it was re-worked into another rock form 3.8bn years ago. That’s a hard distinction to draw.” The same unit of rock contains geological structures which might only have been formed if early life forms were present on the planet, Professor Francis suggested. Early habitat? The material displays a banded iron formation – fine ribbon-like bands of alternating magnetite and quartz. This feature is typical of rock precipitated in deep sea hydrothermal vents – which have been touted as potential habitats for early life on Earth. “These ribbons could imply that 4.3 billion years ago, Earth had an ocean, with hydrothermal circulation,” said Francis. “Now, some people believe that to make precipitation work, you also need bacteria. “If that were true, then this would be the oldest evidence of life. “But if I were to say that, people would yell and scream and say that there is no hard evidence.” Fortunately, geologists have already begun looking for such evidence, in similar rocks found in Greenland, dated 3.8 billion years. “The great thing about our find, is it will bring in people here to Lake Hudson to carry out specialised studies and see whether there was life here or not,” says Francis. “Regardless of that, or the exact date of the rocks, the exciting thing is that we’ve seen a chemical signature that’s never been seen before. That alone makes this an exciting discovery.” http://news.bbc.co.uk/2/hi/science/nature/7639024.stm ————————-
The rocks contain structures which might indicate life was present
 The rocks turned out to be far older than first thought
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Oldest Known Rock on Earth Discovered
Canadian bedrock more than 4 billion years old may be the oldest known section of the Earth’s early crust.
Scientists at the Carnegie Institution of Washington and McGill University in Montreal used geochemical methods to obtain an age of 4.28 billion years for samples of the rock, making it 250 million years more ancient than any previously discovered rocks.
The findings, which offer scientists clues to earliest stages of our planet’s evolution, are published in this week’s issue of the journal Science.
“This research highlights the ways in which new instrumentation [a thermal ionization mass spectrometer, or TIMS] enables the collection of new data–data which lead to major scientific discoveries,” says David Lambert, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research.
The Nuvvuagittuq greenstone belt is an expanse of bedrock exposed on the eastern shore of Hudson Bay in northern Quebec and was first recognized in 2001 as a potential site of very old rocks.
Samples of the Nuvvuagittuq rocks were analyzed by geologists Jonathan O’Neil of McGill University and Richard Carlson of the Carnegie Institution of Washington.
By measuring minute variations in the isotopic composition of the rare earth elements neodymium and samarium in the rocks, O’Neil and Carlson determined that the rock samples range from 3.8 to 4.28 billion years old.
The oldest dates came from rocks termed “faux amphibolite,” which the researchers interpret to be ancient volcanic deposits.
“There have been older dates from Western Australia for isolated resistant mineral grains called zircons,” says Carlson, “but these are the oldest whole rock dates yet.”
The oldest zircon dates are 4.36 billion years.
Before this study, the oldest dated rocks were from a body of rock known as the Acasta Gneiss in the Northwest Territories, which are 4.03 billion years old.
Earth is 4.6 billion years old, and remnants of its early crust are extremely rare–most of it has been mashed and recycled into Earth’s interior several times over by plate tectonics since the planet formed.
The rocks are significant not only for their great age but also for their chemical composition, which resembles that of volcanic rocks in geologic settings where tectonic plates are crashing together. “This gives us an unprecedented glimpse of the processes that formed the early crust,” says Carlson.
The research was also supported by the National Science and Engineering Research Council of Canada, and the Carnegie Institution of Washington.
-NSF-
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