The Shocking Origins of the Oldest Crystals on Earth

Ten years ago, a team of researchers in the US argued that the ancient zircon crystals probably formed when tectonic plates moving around on the Earth’s surface collided with each other in a similar fashion to the disruption taking place in the Andes Mountains today, where the ocean floor under the Pacific Ocean is plunging under South America.However, current evidence suggests that plate tectonics — as we know it today — was not occurring on the early Earth. So, the question remained: Where did the crystals come from?

 To test this idea, researchers from Trinity College Dublin decided to study a much younger impact crater to see if zircon crystals similar to the very old ones could possibly have formed in these violent settings.

In the summer of 2014, with the support of the Irish Reseach Council (IRC) and Science Foundation Ireland (SFI), the team collected thousands of zircons from the Sudbury impact crater, Ontario, Canada – the best preserved large impact crater on Earth and the planet’s second oldest confirmed crater at almost two billion years old.

Credit: Astronauts on Space Shuttle Challenger on flight 41-G

After analyzing these crystals at the Swedish Museum of Natural History in Stockholm, they discovered that the crystal compositions were indistinguishable from the ancient set.PhD Researcher in Trinity’s School of Natural Sciences, Gavin Kenny, is first author of the article which explains these findings, and which has just been published in leading international journal, Geology.He said: “What we found was quite surprising. 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.”

Gavin Kenny recently traveled to the annual Lunar and Planetary Science Conference (LPSC) in Houston, Texas, to present these findings to the space science community.

He added: “There was a lot of enthusiasm for our findings. Just two years ago a group had studied the likely timing of impacts on the early Earth and they suggested that these impacts might explain the ages of the ancient zircons. They were understandably very happy to see that the chemistry of the zircons from the Canadian impact crater matched the oldest crystals known to man.

Contacts and sources:
Thomas Deane

Citation: Kenny GG, Whitehouse MJ, Kamber BS. Differentiated impact melt sheets may be a potential source of Hadean detrital zircon. Geology. 2016; DOI: 10.1130/G37898.1 http://dx.doi.org/10.1130/G37898.1