An Ancient Impact That Dwarfs The Dinosaur-Killing Blast


Comparing Impactor SIzes


The collision punches a crater into the planet's crust that's nearly 500 kilometers (about 300 miles) across: greater than the distance from Washington, D.C., to New York City, and up to two and a half times larger in diameter than the hole formed by the dinosaur-killing asteroid. Seismic waves bigger than any recorded earthquakes shake the planet for about half an hour at any one location -- about six times longer than the huge earthquake that struck Japan three years ago. The impact also sets off tsunamis many times deeper than the one that followed the Japanese quake.


The huge impactor -- between 37 and 58 kilometers (23 to 36 miles) wide -- collided with the planet at 20 kilometers per second (12 miles per second). The jolt, bigger than a 10.8 magnitude earthquake, propelled seismic waves hundreds of kilometers through the Earth, breaking rocks and setting off other large earthquakes. Tsunamis thousands of meters deep -- far bigger than recent tsunamis generated by earthquakes -- swept across the oceans that covered most of the Earth at that time.

"We knew it was big, but we didn't know how big," Donald Lowe, a geologist at Stanford University and a co-author of the study, said of the asteroid.





The impact may have been one of dozens of huge asteroids that scientists think hit the Earth during the tail end of the Late Heavy Bombardment period, a major period of impacts that occurred early in the Earth's history -- around 3 billion to 4 billion years ago.

Many of the sites where these asteroids landed were destroyed by erosion, movement of the Earth's crust and other forces as the Earth evolved, but geologists have found a handful of areas in South Africa, and Western Australia that still harbor evidence of these impacts that occurred between 3.23 billion and 3.47 billion years ago. The study's co-authors think the asteroid hit the Earth thousands of kilometers away from the Barberton Greenstone Belt, although they can't pinpoint the exact location.

"We can't go to the impact sites. In order to better understand how big it was and its effect we need studies like this," said Lowe. Scientists must use the geological evidence of these impacts to piece together what happened to the Earth during this time, Lowe said.

The study's findings have important implications for understanding the early Earth and how the planet formed. The impact may have disrupted the Earth's crust and the tectonic regime that characterized the early planet, leading to the start of a more modern plate tectonic system, according to the paper's co-authors.


The geological evidence found in the Barberton that the paper investigates indicates that the asteroid was "far larger than anything in the last billion years," said Jay Melosh, a professor at Purdue University in West Lafayette, Indiana, who was not involved in the research.



"This is providing significant support for the idea that the impact may have been responsible for this major shift in tectonics," he said.

Reconstructing the asteroid's impact could also help scientists better understand the conditions under which early life on the planet evolved, the paper's authors said. Along with altering the Earth itself, the environmental changes triggered by the impact may have wiped out many microscopic organisms living on the developing planet, allowing other organisms to evolve, they said.

"We are trying to understand the forces that shaped our planet early in its evolution and the environments in which life evolved," Lowe said.

PIO Contact:
Nanci Bompey
+1 (202) 777-7524

Science Contact:
Norman Sleep
+1 (650) 723-0882


"Physics of crustal fracturing and chert dike formation triggered by asteroid impact, ~3.26 Ga, Barberton greenstone belt, South Africa," Norman H. Sleep (Department of Geophysics, Stanford University, Stanford, CA, USA) and Donald R. Lowe (Department of Geological and Environmental Sciences, Stanford University, Stanford, CA, USA). Journalists and public information officers (PIOs) of educational and scientific institutions who have registered with AGU can download a PDF copy of the research paper at http://onlinelibrary.wiley.com/doi/10.1002/2014GC005229/abstract or may order a copy of the paper by emailing your request to Nanci Bompey at nbompey@agu.org. Please provide your name, the name of your publication, and your phone number.

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