Nuvvuagittuq greenstone, Nuvvuagittuq greenstone Hudson bay

How Old Is the Hudson Bay Greenstone?

September 29, 2008 03:25 PM
by Sarah Amandolare
Rock found in Hudson Bay, Canada, could be the oldest ever discovered, and might provide insight into ancient life; but geologists debate the dating methods.

Dating the Oldest Rocks on Earth

A team of geologists has found what could be the oldest rock ever documented, a sample of Nuvvuagittuq greenstone that could be 4.28 billion years old, “250 million years older than any rocks known,” reports the BBC. The discovery occurred in Canada, on the shores of Hudson Bay, and could be “the earliest evidence of life on Earth.”

The sample of greenstone contains a unique chemical signature, “a banded iron formation—fine ribbon-like bands of alternating magnetite and quartz,” indicative of ancient deep seas, which could mean that Earth had an ocean 4.3 billion years ago.

According to team member Don Francis, “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.”

The finding is considered rare because most of Earth’s original surface “has been crushed and recycled through movement of giant tectonic plates,” according to The Daily Mail.

Furthermore, the discovery is significant because it offers researchers insight into “early separation of Earth’s mantle from the crust in the Hadean Era,” team member Jonathan O’Neil told Science Daily.

“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,” O’Neil said.

But the team’s method of dating the rock remains controversial. According to New Scientist, the technique is based on measuring the rock’s content of neodymium-142, a common isotope present in all rocks, but more prevalent in rocks older than 4.2 billion years old. There is some question, however, of whether the team actually measured “the age of the magma from which the rocks formed,” rather than the rock itself.
The team also measured the greenstone belt’s age using “a conventional method,” which suggested the rock is only 3.8 billion years old, leading some to dispute the true age. Simon Wilde from Australia’s Institute for Geoscience Research said, “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.”

Regardless, the finding is likely to lead to further study in the area. “Any shred of evidence is important in trying to reconstruct” the evolution of Earth, said Martin Whitehouse of the Swedish Museum of Natural History.

Background: Nuvvuagittuq greenstone and the Hadean Eon

Live Science explains that it is rare to find “remnants of crust from Earth’s infancy … because most of that material has been recycled into Earth’s interior” by plate tectonics. Therefore, when the Nuvvuagittuq greenstone belt in Hudson Bay was found by geologists in 2001, and was suspected to be “from one of the earliest periods of Earth’s history,” further studies were called for.

If it is determined that the greenstone belt’s age is indeed 4.28 billion years old, it could provide insight into the Hadean Era.

According to Live Science, the Hadean eon refers to “all Earth time prior to 3.8 billion years ago,” during which it was too hot and volcanic for living things to survive. But in 2005, new research suggested that the Hadean era might not have been as harsh and averse to life as was previously believed. 

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