Origin of Earth's oldest crystals revealed

​London: The very oldest pieces of rock on Earth -- zircon crystals -- are likely to have formed in the craters left by violent asteroid impacts that peppered our nascent planet rather than via plate tectonics as previously believed, researchers report.

The tiny crystals probably formed in huge impact craters not long after Earth formed, some four billion years ago.Rocks that formed over the course of Earth's history allow geologists to infer things such as when water first appeared on the planet, how our climate has varied, and even where life came from.

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. 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?

Recently, geologists suggested these grains may have formed in huge impact craters produced as chunks of rock from space, up to several km in diameter, slammed into a young Earth.

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.