Earth's oldest rocks date back 4.16 billion years
While rocks are not exactly living things, they are not immune to Earth's fury. Ever-shifting tectonic plates constantly devour and pulverize them, or some rocks get turned into diamonds from the immense pressure underneath our feet. While life on Earth has almost been wiped out at least five times, some rocks pre-date life on Earth and have stood the ultimate test of time.
Gray rocks uncovered in northern Nunavik, Quebec, Canada may be the ultimate primordial find. The stones date back 4.16 billion years to the Hadean era and are the oldest known rocks on the planet. They are described in a study published June 26 in the journal Science.
Earth was a ball of molten lava when it first formed about 4.5 billion years ago. Scientists originally believed that Earth's first eon–the Hadean–ended when the first rocks formed. A golden spike–a geological marker indicates a boundary between time periods–that ended the Hadean eon is about 4.03 billion years old and located in Canada's Northwest Territories.
The Nuvvuagittuq Greenstone Belt, located over 1,000 miles southeast of the Hadean's golden spike, has long been known for its ancient rocks. However, researchers have disagreed about the true age of these plains of gray stone that line the eastern shore of Hudson Bay in Quebec. In 2008, researchers proposed that these rocks dated back 4.3 billion years. Other scientists using a different dating method contested, saying that contaminants from ages ago were altering the rocks' age and they were only 3.8 billion years old.
'For over 15 years, the scientific community has debated the age of volcanic rocks from northern Quebec,' study co-author and University of Ottawa geologist Jonathan O'Neill said in a statement. 'Our previous research suggested that they could date back 4.3 billion years, but this wasn't the consensus.'
[ Related: How old is Earth? It's a surprisingly tough question to answer. ]
This new study used rock samples from a different part of the Nuvvuagittuq Greenstone Belt. The samples were collected in 2017 near the municipality of Inukjuak, Nunavik, by study co-author Christian Sole, while was completing his Master's degree.
To determine the age of these rocks, the team combined geochemistry with petrology–a branch in geology that focuses on the composition, texture, and structure of rocks and the conditions under which they form. They also applied two radiometric dating methods to see how radioactive isotopes of the elements samarium and neodymium change over time.
[ Related: Ancient rocks tie Roman Empire's collapse to a mini ice age. ]
They found that both chronometers indicated that the rocks are 4.16 billion years old. Since the planet Earth formed roughly 4.5 billion years ago, this puts the rocks within a few hundred million years of our planet's earliest day–somewhat close in geological time. Typically, primordial rocks like these are melted and used over and over again by Earth's moving tectonic plates. While scientists uncovered some 4 billion-year-old rocks in Canada's Acasta Gneiss Complex, finding them at the surface is not common.
According to the team, this discovery opens a unique window on the early Earth, potentially offering up clues to its existence.
'Understanding these rocks is going back to the very origins of our planet,' O'Neill said. 'This allows us to better understand how the first continents were formed and to reconstruct the environment from which life could have emerged.'
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