Australian researchers have uncovered what might be the biggest impact asteroid impact zone in the world – at over 400 kilometers (250 miles)!

Image credit: A.Y. Glikson et al.

Naturally, the crater isn’t visible today, but geophysicists have found the impact’s scars deep below the surface. Lead researcher Dr Andrew Glikson from the ANU School of Archaeology and Anthropology explains:

“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,” said Dr Glikson.

The material from the two sites seems very similar, so this made geologists believe that they are actually part of the same huge asteroid, which probably broke in half upon entering the atmosphere. The drill actually recovered traces of rocks that had been turned to glass by the extreme temperature and pressure – a smoking gun for an asteroid hit.

The twin scars of the impact were discovered rather unexpectedly during drilling as part of geothermal research, in the Warburton Basin. The exact date of the impact remains unclear; the only solid information we have so far is that the surrounding rocks are between 300 and 450 million years old – but that’s quite a large uncertainty. Still, their findings seem to be consistent with previous geophysical studies.

“The pre-Upper Carboniferous ~ 450 × 300 km-large Warburton Basin, north-eastern South Australia, is marked by distinct eastern and western magnetic, gravity and low-velocity seismic tomography anomalies.”

Warburton East and West sub-basins, northeast South Australia; the Birdsville Track Ridge divides the Warburton East Basin from the Warburton West Basin. Image credit: A.Y. Glikson et al.

These impacts may have had a more significant impact on life on Earth than is currently assumed.

“Large impacts like these may have had a far more significant role in the Earth’s evolution than previously thought,” Dr Glikson said.

However, unlike the meteorite that wiped out the dinosaurs and many other species 66 million years ago (and whose crater was found only in the 1970s), there seems to be no major extinction connected to this event, and no other geological phenomenon associated with it (such as increased volcanic activity for example).

“When we know more about the age of the impact, then we will know whether it correlates with one of the large mass extinctions [at the end of specific eras]. At this stage we do not have all the answers, but there has been a lot of interest and people are certainly interested in any impact on the dinosaurs.”

Magnetic modelling of the area also revealed bulges hidden deep in the Earth, rich in iron and magnesium, corresponding to the composition of the Earth mantle. The impact zones seem to impact throughout the entire Earth’s crust, all the way down to the mantle.

“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,” Dr Glikson said.

Journal Reference: A.Y. Gliksona, A.J. Meixnere, B. Radke, I.T. Uysal, E. Saygin, J. Vickers, T.P. Mernagh. Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia. doi:10.1016/j.tecto.2014.12.010