The oldest known rock on Earth is found along the northeast coast of Hudson Bay, Canada. Click on image for full size (341 Kb) Courtesy of Jonathan O'Neil

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.

Text above is courtesy of the National Science Foundation

The oldest known rock on Earth is found along the northeast coast of Hudson Bay, Canada. Click on image for full size (341 Kb) Courtesy of Jonathan O'Neil

Earth is old, 4.6 billion years old to be exact. But there isn’t much hanging around the planet from those early days. That’s because our planet is a great recycler. Most of the rocks that were formed when Earth was young have been mashed, melted, or eroded into sand as plate tectonic forces move them around. So remnants of Earth’s early crust are extremely rare.

But recently, geologists found rocks from Canada that formed 4.28 billion years ago. That’s 250 million years older than any other known rocks. They used a new instrument called a thermal ionization mass spectrometer to learn about the rocks’ age and geochemistry. By measuring the small amounts of two rare earth elements in the rocks, the geologists could measure the age of the rocks. Some of the rock samples were as young as 3.8 billion years old. Others were as much as 4.28 billion years old. These oldest rocks may have formed from ancient volcanoes.

These rocks come from an area on the eastern shore of Hudson Bay in northern Quebec called the Nuvvuagittuq greenstone belt. Scientists have known for several years that the rocks in this area were very old. Now we know how old.

Individual mineral grains called zircons are still the oldest part of the Earth’s geosphere. Zircon grains, which come from Western Australia, are 4.36 billion years. Before this study, the oldest dated whole rocks were from Canada’s Northwest Territories, which are 4.03 billion years old.

The oldest known rock on Earth is found along the northeast coast of Hudson Bay, Canada. Click on image for full size (341 Kb) Courtesy of Jonathan O'Neil

Earth is more than four and a half billion years old. But there are very few things around from the Earth’s early days. That’s because our planet is a great recycler. Most of the rocks that were formed when Earth was young have been mashed, melted, or eroded into sand as plate tectonic forces move them around. So pieces of rock from the Earth’s early crust are not easy to find.

But recently, scientists found rocks from Canada that are 250 million years older than any other known rocks. The scientists studied the chemistry of the rocks to find out how old they are. Some of the rock samples were as young as 3.8 billion years old. Others were as much as 4.28 billion years old. These oldest rocks may have formed from ancient volcanoes.

These rocks come from an area on the eastern shore of Hudson Bay in northern Quebec called the Nuvvuagittuq greenstone belt. Scientists have known for several years that the rocks in this area were very old. Now we know how old!