The devastating event took place on our planet many millions of years ago, but researchers are only now beginning to discover what happened.
In a remote part of Central Australia, the two pieces of asteroid left what geophysicists say is the largest impact zone ever found on Earth, spreading over an area 400 kilometers (250 miles) wide.
"The two asteroids must each have been over 10 kilometers across -- it would have been curtains for many life species on the planet at the time," said lead researcher Andrew Glikson of the Australian National University
The team published its research in the journal Tectonophysics
The crater caused by the asteroids vanished long ago. But Glikson said the researchers stumbled across scars from the impacts during drilling for geothermal research.
Traces are buried more than 2 kilometers inside the Earth's crust, under an area near the borders of South Australia, Queensland and the Northern Territory.
"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.
Mystery over timing
The researchers are still trying to figure out just how long ago the shattering event happened.
The surrounding rocks are 300 million to 600 million years old, according to the team, but they haven't been able to find the sort of evidence left by other meteorite strikes.
A big meteorite strike that is believed to have led to the extinction of many dinosaur species 66 million years ago launched a plume of ash into the air that now shows up as a layer of sediment in rocks.
But the researchers say they haven't come across a similar layer in sediments from about 300 million years ago.
"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," Glikson said.
The discovery of the huge asteroid impacts could lead to new insights about the Earth's history.
"Large impacts like these may have had a far more significant role in the Earth's evolution than previously thought," Glikson said.