Oldest rocks ever discovered on Earth (4.28 Ga).

Published 2008-09-26 by Chris

A recent Science Paper (as reported by Nature and Science Centric) has dated rock samples from the Nuvvuagittuq greenstone belt, on the eastern edge of Hudson Bay in Quebec, Canada, at a staggering 4.28 billion years old. The research team used the (somewhat unconventional for terrestrial dating) ¹⁴⁶Sm→¹⁴²Nd isotopic system, due to the lack of zircon being found within the rock. This means the date will have to be confirmed, preferably with zircons, for many to lend weight to the claims, but all the same, this is an amazing discovery.

It’s pretty staggering how old these rocks are. So let’s put it into perspective:

These rocks were formed 270 millions years after the Earth (4.55 Ga), which means they’ve remained reasonably unchanged for almost the entire history of the planet. They’ve survived 4.28 billions years of: plate tectonics including subduction and obduction, glacial erosion, meteorological erosion, chemical erosion, chemical alteration (maybe), or any other method of rock recycling. It also means we have pushed back the earliest date for continental material existing on Earth by 250 million years (the previous record was 4.03 Ga for the Acasta Gneiss, also from Canada).

These aren’t the oldest terrestrial material ever discovered, however. That title still belongs to zircons from the Jack Hills in Western Australia, that have been dated at a positively geriatric 4.4 GYr. But as a sample of rock, this is pretty exciting so far as early Earth chronology goes.

Geological timescale thanks to Chris Rowan at Highly Allochthonous.
Splash image to the left lifted from Nature, and courtesy of AAAS/Science.

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