Nuvvuagittuq Greenstone Belt May Hold 4.16-Billion-Year-Old Minerals

A band of swirling, striped rock in Canada’s far north-east appears to hold some of the oldest minerals ever identified at Earth’s surface.

A fresh mineral-dating study of the Nuvvuagittuq Greenstone Belt indicates that sections of the formation may be 4.16 billion years old - almost as old as Earth itself, which is 4.54 billion years old. These findings make the belt one of the most valuable locations for investigating our planet’s earliest history.

"For over 15 years, the scientific community has debated the age of volcanic rocks from northern Quebec," says geoscientist Jonathan O'Neil of the University of Ottawa in Canada.

"This confirmation positions the Nuvvuagittuq Belt as the only place on Earth where we find rocks formed during the Hadean eon."

Why ancient minerals are so valuable

Earth’s crust and surface are perpetually changing. Tectonic activity beneath the ground, together with weathering at the surface, keeps the planet in a constant state of transformation. It is therefore rare for surface features to endure for billions of years.

Locations where very old minerals have somehow escaped time’s destructive effects are exceptionally important to science. They can reveal what Earth was like while it was taking shape, before life emerged from primordial chemistry.

The significance extends well beyond our small blue planet. Earth is the only world known with certainty to support life, so learning how it formed, developed and changed may help scientists identify comparable planets elsewhere in the galaxy.

Dating the Nuvvuagittuq Greenstone Belt

Scientists have long regarded the Nuvvuagittuq Greenstone Belt as a possible repository of Hadean minerals. The Hadean was the first of Earth’s four geological eons, lasting from the planet’s formation until a little more than 4 billion years ago. Earlier attempts to date minerals believed to be ancient, however, produced unclear and contradictory ages ranging from roughly 4.3 billion to 2.7 billion years.

A research group led by University of Ottawa geoscientist Christian Sole therefore chose another method. Previous analyses had assessed ratios between radioactive atoms and isotopes produced through their decay in basaltic rock.

The most dependable isotope-dating technique uses zircon crystals. As zircon forms, it incorporates tiny quantities of uranium while strongly excluding lead. Uranium subsequently decays into lead within the crystal, meaning any lead in zircon must originate from uranium’s radioactive decay. Since uranium’s decay rate is precisely known, these ratios can be used to date zircon accurately.

Basaltic rock such as that in the Nuvvuagittuq Greenstone Belt does not readily form zircon, which is why many earlier studies instead examined radioactive samarium and the neodymium isotopes produced by its decay. That approach is less reliable than uranium-lead dating.

Sole and his team adopted a different strategy, examining large metagabbro inclusions. Metagabbro is a rock that began as the igneous rock gabbro before being transformed by heat and pressure within Earth’s crust. Because these metagabbros intruded into older basalts, they establish a minimum age for the surrounding basalt matrix.

The researchers analysed their specimens using both lead-uranium and samarium-neodymium dating. Each method delivered the same outcome, including for rocks with differing mineral compositions collected from separate sites: the Nuvvuagittuq Greenstone Belt has a minimum age of 4.16 billion years.

What the 4.16-billion-year age could reveal

The finding creates promising opportunities to explore Earth’s earliest era in greater detail.

"Understanding these rocks is going back to the very origins of our planet," O'Neil says. "This allows us to better understand how the first continents were formed and to reconstruct the environment from which life could have emerged."

The research has been published in Science.