Earth's oldest rocks came from asteroids, study reports

A new study suggests that the oldest rocks on Earth came from ancient meteorite impacts.
By Joseph Scalise | Jan 03, 2019
A group of researchers from the Curtin University have found evidence that Earth's oldest rocks once came from meteors traveling through space, according to a new study published inthe journal Nature Geoscience.

The theory -- which argues that a meteorite bombardment created the ancient stones -- states such an event is the only way to explain the temperature and pressure conditions that formed the oldest rocks on our world.

"We believe that these rocks may be the only surviving remnants of a barrage of extraterrestrial impacts which characterized the first 600 million years of Earth's history," said lead study author Tim Johnson, a geologist at Curtin University, according toSpace.com.

To make the findings, scientists analyzed a 4-billion-year-old rock type -- known as Idiwhaa gneiss -- in northwest Canada. They looked at the chemical composition of the rocks and then modeled how they first formed. That revealed they came about through low pressures and temperatures that reached 1,650 degrees Fahrenheit.

Those conditions almost never happen under normal circumstances. When temperatures hit those levels, pressures need to be much higher. To explain that, the team turned to meteorites.

They found that in the early days of Earth impacts from space rocks would have been able to raise temperatures enough to melt rocks at the top of the crust without increasing pressure. Though most of the rocks created during that time fell back into Earth's interior, the Idiwhaa rocks are still around to give insight into that ancient time.

"The idea of making felsic melts by large or giant impacts seems plausible considering the high-energy nature of these events and the pockmarked ancient surfaces of other inner Solar System planets and moons," said Balz Kamber, a researcher from Trinity College Dublin who was not involved in the research, according to Phys.org.

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