April 10, 2014
Stanford Researchers Model Massive Asteroid Impact
Brett Smith for redOrbit.com - Your Universe Online
Earth was irrevocably changed when the dinosaurs were wiped out about 65 million years ago by a massive asteroid, but a much bigger asteroid that struck the Earth nearly 3.3 billion years ago is thought to have shaped parts of Africa.
Now, a new study published in the journal Geochemistry, Geophysics, Geosystems has outlined the details surrounding that massive impact, such as the creation of a crater about 300 miles across and earthquakes that shook the planet for around 90 minutes.
Based on extensive modeling, the study said the massive asteroid was between 23 and 36 miles wide and it impacted the Earth at a speed of about 12 miles per second. The strike, equivalent to a 10.8 magnitude earthquake, propelled seismic waves hundreds of miles through the planet – splitting stones and releasing large earthquakes. Massive tsunamis swept across the enormous ocean that covered Earth at the time.
The study was based on Lowe’s discovery of telltale stone formations in the Barberton greenstone of South Africa a decade ago. He said he thought their unique composition pointed to an asteroid impact. The new study replicates just how big the asteroid was and the effect it had on the planet, including the probable initiation of the plate tectonic system seen in the region today, according to Lowe.
The study team said the sky would have become super-heated, the atmosphere would have loaded up with dirt and the ocean surface would have boiled as a result of the impact. The collision sent vaporized stone into the atmosphere, which surrounded the globe and condensed into liquid droplets before solidifying and dropping to the surface, the study team explained.
As unique as this asteroid impact sounds, the study team also said that it was probably just one of many such events that occurred around 3 billion to 4 billion years ago, a time known as the Late Heavy Bombardment period. Many of the impact craters generated during this period have subsequently been eliminated by millennia of erosion, movement of Earth’s crust and other factors. However, geologists have discovered a couple of areas in South Africa and Western Australia that still possess evidence of these strikes that happened between 3.2 billion and 3.5 billion years ago.
“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.
The study authors said the asteroid strike was probably thousands of miles away from the Barberton Greenstone Belt, although they can’t target the precise locale. They added that studies like these use geological evidence to determine what happened to the Earth during this time.
Frank Kyte, a geologist at UCLA who was not involved in the study, said the modeling used by the researchers does provide evidence for the creation of the formations in the Barberton greenstone belt.
“This is providing significant support for the idea that the impact may have been responsible for this major shift in tectonics,” he said.
“We are trying to understand the forces that shaped our planet early in its evolution and the environments in which life evolved,” Lowe added.
Image 2 (below): A graphical representation of the size of the asteroid thought to have killed the dinosaurs, and the crater it created, compared to an asteroid thought to have hit the Earth 3.26 billion years ago and the size of the crater it may have generated. A new study reveals the power and scale of the event some 3.26 billion years ago which scientists think created geological features found in a South African region known as the Barberton greenstone belt. Credit: American Geophysical Union