WA zircon sheds light on baby Earth
For its first few hundred million years, the Earth was barren, flat and almost entirely under water, Australian scientists say.
Australian National University (ANU) experts have analysed tiny zircon mineral grains up to 4.4 billion years old, preserved in sandstone rocks in the Jack Hills of Western Australia, some of the oldest fragments of the Earth ever found.
“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,” said Dr Burnham from the ANU Research School of Earth Sciences.
“Our research indicates there were no mountains and continental collisions during Earth's first 700 million years or more of existence - it was a much more quiet and dull place.
“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.
“We used the granites of southeast Australia to decipher the link between zircon composition and magma type, and built a picture of what those missing rocks were,” he said.
Life emerged later, around 3.8 billion years ago.
The zircon formed by melting older igneous rocks rather than sediments.
“Sediment melting is characteristic of major continental collisions, such as the Himalayas, so it appears that such events did not occur during these early stages of Earth's history,” Dr Burnham said.
“The samples of zircon from Jack Hills have been collected over the course of several decades by many people, while chemical analyses carried out by an ANU research group 20 years ago have proved invaluable.”
The study is accessible here.