Geologists Have Discovered the Likely Origins of Earth’s Oldest Crystals

Let’s just say it is not from the gentlest of processes.

Earth has been around the block a few times — more than 4.5 billion times in fact. In its travels, the planet has been bombarded by asteroids and comets, extremely heated and cooled, and experienced numerous mass extinctions. But despite this maturity, Earth has a fairly young looking surface — and it has nothing to do with anti-aging creams.

Thanks to plate tectonics, most of Earth’s surface is a lot younger than its age. And this makes studying Earth’s early history — including when water first appeared on the planet or how the climate has varied — a little tricky because we can only go back in time so far. In fact, the only material we have from very early Earth comes in the form of tiny, naturally occurring zircon crystals, which are estimated to be more than four billion years old.

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Current evidence has suggested that plate tectonics — as we know it today — was not occurring on early Earth and that it did not begin until roughly three billion years ago. So where did the crystals come from?

Enter the impact crater hypothesis.

New research suggests that these zircon crystals, which are approximately the width of a human hair, likely formed in craters left by asteroid impacts, rather than via plate tectonics.

To test this idea, researchers from Trinity College Dublin traveled to Sudbury, Ontario, Canada, to study a much younger impact crater to see if they could uncover similar zircon crystals. And in the summer of 2014, the team collected thousands of zircons from the Sudbury impact crater — the best preserved and second oldest confirmed impact crater on Earth at almost two billion years old.

After analyzing the crystals at the Swedish Museum of Natural History in Stockholm, the researchers discovered that the crystal compositions were indistinguishable from the 4-billion-year-old ones.

"What we found was quite surprising," said Gavin Kenny, first author of the article and doctoral candidate at Trinity’s School of Natural Sciences, in a press release. "Many people thought the very ancient zircon crystals couldn't have formed in impact craters, but we now know they could have."

"There's a lot we still don't fully understand about these little guys but it looks like we may now be able to form a more coherent story of Earth's early years -- one which fits with the idea that our planet suffered far more frequent bombardment from asteroids early on than it has in relatively recent times," he continued.

The paper has been published in the international journal, Geology.

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