Tiny zircon crystals have allowed scientists at Australian National University (ANU) to paint a portrait of what Earth looked like over four billion years ago. Their scrutiny of the mineral grains – the oldest fragments of the planet we’ve ever uncovered – led them to think our world was a much different place back then. They say the planet, which was barren, had no mountains, and probably only a few islands poked up above the water blanketing the rest of the planet.
Zircon crystals preserved inside sandstone rocks in the Jack Hills of Western Australia provided clues to our planet’s history – billions of years before humans ever showed up. Lead researcher Antony Burnham said the zircon samples were collected over multiple decades, and his team also drew on chemical analyses from an ANU research group two decades ago. He likened zircon grains to skin cells at a crime scene.
“The history of the Earth is like a book with its first chapter ripped out with no surviving rocks from the very early period, but we’ve used these trace elements of zircon to build a profile of the world at that time,” he said in a statement. “Our research indicates there were no mountains and continental collisions during the Earth’s first 700 million years or more of existence – it was a much more quiet and dull place.”
The zircon formed from melting older igneous rocks, instead of sediment melting, which is typical in continental collisions. And it appears it took a long time for the planet to change from the flat landscape into the Earth we inhabit now.
“Our findings also showed that there are strong similarities with zircon from the types of rocks that predominated for the following 1.5 billion years, suggesting that it took the Earth a long time to evolve into the planet that we know today,” Burnham said.