A study of ancient rocks in Australia – combined with computer modeling of the early solar system – has led researchers to estimate that approximately 70 killer asteroids of the same size that caused the extinction of the dinosaurs or larger struck Earth 1.8 to 3.8 billion years ago. During the same period, approximately four similarly-sized objects hit the moon. Scientists with NASA’s Lunar Science Institute and international scientists published these results yesterday (April 25, 2012) in the journal Nature.
Part of the evidence for these early impacts on Earth by killer asteroids comes from thin rock layers in Australia. The rocks contain debris of nearly spherical, sand-sized droplets called spherules. The scientists say these rocks consist of formerly molten droplets ejected into space within the huge plumes created by mega-impacts on Earth.
The demise of the dinosaurs occurred more recently than the asteroids suggested by this study, only about 65 million years ago in contrast to 1.8 to 3.8 billion years ago. Scientists believe that the killer asteroid that impacted Earth 65 million years ago would have been almost 6 miles (10 kilometers) in diameter.
This science team used computer modeling to depict a time in the early solar system, billions of years ago. They call on the giant planets Jupiter, Saturn, Uranus and Neptune to help send killer asteroids hurtling to Earth. They say their study supports the idea that the giant planets formed in different orbits from where we see them today nearly 4.5 billion years ago. The theory is that the giant worlds migrated to their current orbits about 4 billion years ago from the interplay of gravitational forces in the young solar system. According to the theory, this event triggered a solar system-wide bombardment of comets and asteroids called the Late Heavy Bombardment by scientists. In yesterday’s Nature paper, the team describe a model they created with computers, showing what the asteroid belt might have looked like at that early time. They then tracked what would have happened when the orbits of the giant planets changed.
They discovered the innermost portion of the asteroid belt became destabilized and could have delivered numerous big impacts to Earth and the moon over long time periods.
Further evidence for these early impacts on Earth by killer asteroids comes from thin rock layers in Australia. The rocks contain debris of nearly spherical, sand-sized droplets called spherules. These circles and particles are formerly molten droplets ejected into space when an asteroid hit the Earth 2.63 billion years ago, according to this study.
Bottom line: Scientists studying ancient rocks in Australia and using a computer model to depict the early solar system now say that approximately 70 killer asteroids 6 miles (10 kilometers) – or larger – impacted Earth 1.8 to 3.8 billion years ago, and approximately four similarly-sized objects hit the moon around that time. Scientists with NASA’s Lunar Science Institute and international scientists published these results April 25, 2012 in the journal Nature..
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.