Andrew Glikson examines a rock with fragments of glass made by the high heat and pressure of a meteorite impact. Photo by D. Seymou/ANU
ACTON, Australia, March 23 (UPI) -- There's no hole or depression to speak of. The newly discovered meteorite crater has been filled in -- and much of the evidence weathered away -- over the last 300 million-plus years, but a couple of massive scars remain.
Researchers only recently identified the scars in the Australian outback as the product of an ancient meteorite -- a meteor that split in two just before impact, creating the largest known meteorite crater.
Initially, scientists located only a single scar. That was five years ago. The first scar, alone, constituted the third largest meteorite impact site on Earth.
But now, researchers from the Australian National University have identified a second scar, which scientists say was likely made by the same massive chunk of space rock as the first. Each impact site measures 120 miles in diameter. Together, the two sites makeup the largest meteorite crater in the history of Earth.
"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," lead researcher Andrew Glikson, a professor at the ANU School of Archaeology and Anthropology, said in a press release.
The researchers legitimized the scars' origin story with followup research, drilling deep into the crust below and using electromagnetic imaging to model the rock composition below the surface. The drill core revealed fragments of rocks that had turned to glass -- the kind of transformation only made possible by the high pressure and extreme heat of massive impacts.
Magnetic image modeling helped scientists locate two massive bulges of rock rich in iron and magnesium buried deep below the surface.
"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," Glikson said.
While the tentative date for the impact has been placed at 300 million years ago, researchers haven't been able to match it up with an extinction event in the geologic record. Nearby rock dates as far back as 600 million years, leading researchers to suggest there's a chance the massive impact is older than currently estimated.
"The consequences are that it could have caused a large mass extinction event at the time, but we still don't know the age of this asteroid impact and we are still working on it," Glikson told the Australian Broadcasting Corporation.
The research was published this week in the journal Tectonophysics.