Meteorites key to Earth's layer formation

New research proves crust formed 4.5 billion years ago

Dr Yuri Amelin explained how knowledge of the composition of the original material that formed Earth has enabled the team to determine how and when its layers formed.
Credit: Stuart Hay

Scientists have conducted a new analysis of meteorites to determine when Earth’s layers were formed.

The research, published in Proceedings of the National Academy of Sciences, has confirmed that Earth’s crust was formed some 4.5 billion years ago.

An international team of scientists measured the amount of the elements hafnium and lutetium in the mineral zircon, taken from a meteorite that originated early in the solar system.

"Meteorites that contain zircons are rare. We had been looking for an old meteorite with large zircons, about 50 microns long, that contained enough hafnium for precise analysis," says Dr Yuri Amelin from The Australian National University (ANU) Research School of Earth Sciences.

"By chance we found one for sale from a dealer. It was just what we wanted. We believe it originated from the asteroid Vesta, following a large impact that sent rock fragments on a course to Earth."

Enormous heat and pressure in Earth's interior mixes up the chemical composition of its layers over billions of years, meaning dense rocks sink and less dense minerals rise towards the surface. This process is known to as differentiation.

“Meteorites are remnants of the original pool of material that formed all the planets," Dr Amelin says. "But they have not had planetary-scale forces changing their composition throughout their five billion years orbiting the Sun."

The research team first measured the ratio of isotopes hafnium-176 and hafnium-177 in the meteorite in order to determine a starting point for the composition of Earth’s interior. Comparing this data with the oldest rocks on Earth indicated that its chemical composition had already been altered by that stage, proving a crust had formed on Earth’s surface as long as 4.5 billion years ago.


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