An asteroid that broke in two moments before crashing into Earth created a 400 kilometre (248 mile) wide impact zone in Central Australia, researchers from the Australian National University’s School of Archaeology and Anthropology reported.
The resulting crater, which was formed millions of years ago, has long gone. However, a team of geophysicists say they have discovered the twin scars of the impacts – the largest asteroid impact zone so far found on Earth – hidden deep below the surface.
The findings have been published in the academic journal Tectonophysics.
Dr Andrew Glikson examining a sample of suevite – a rock with partially melted material formed during an impact. (Image: D. Seymour)
Study leader, Dr. Andrew Glikson, said the impact zone, located in an area near the borders of the Northern Territory, Queensland and South Australia, was discovered during drilling in a geothermal research project.
Two asteroids 10 km wide
Dr. Glikson said:
“The two asteroids must each have been over 10 kilometres across – it would have been curtains for many life species on the planet at the time.”
The scientists say the discovery of such ancient violent impacts could lead to new theories regarding the Earth’s History.
Dr. Glikson said:
“Large impacts like these may have had a far more significant role in the Earth’s evolution than previously thought.”
The geophysicists say they are not sure when exactly the impacts took place. The rocks in the area are 300 to 600 million years old, but there is no evidence of the type left by other meteorite strikes.
When the asteroid entered the Earth’s atmosphere it split into two giant meteors.
For example, a large impact that occurred 66 million years ago sent up a huge plume of ash which can be found as a layer of sediment in rocks across our planet. The plume is believed to have led to the extinction of a significant proportion of life on Earth, including several species of dinosaurs.
No evidence of an ash plume
However, no similar layer has been found in sediments dating back 300 million years, the scientists explained.
Dr. Glikson said:
“It’s a mystery – we can’t find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years.”
A geothermal research project came across evidence of the impacts while drilling over two kilometres into the Earth’s crust.
They found traces of rocks on the drill core that had been turned to glass by the extremely high temperature and pressure caused by a massive impact.
Magnetic modelling of the deep crust in the area revealed bulges deep within the Earth, rich in magnesium and iron, corresponding to the composition of the Earth mantle.
Dr. Glikson said:
“There are two huge deep domes in the crust, formed by the Earth’s crust rebounding after the huge impacts, and bringing up rock from the mantle below.”
The two impacts, in the Warburton Basin in Central Australia, are over 400 km across. They extend through the Earth’s crust, which is approximately 30 km thick in this area.
Citation: “Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia,”
A.Y. Glikson, .J. Meixner, B. Radke, I.T. Uysal, E. Saygin, J. Vickers and T.P. Mernagh. Tectonophysics, Volume 643, Published March 7, 2015.