NASA Scientists Find History of Asteroid Impacts in Earth Rocks

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Source: NASA RELEASE : 12-135 
Excerpt: … Research by NASA and international scientists concludes giant asteroids, similar or larger than the one believed to have killed the dinosaurs, hit Earth billions of years ago with more frequency than previously thought. To cause the dinosaur extinction, the killer asteroid that impacted Earth 65 million years ago would have been almost 6 miles (10 kilometers) in diameter. By studying ancient rocks in Australia and using computer models, researchers estimate that approximately 70 asteroids the same size or larger impacted Earth 1.8 to 3.8 billion years ago. During the same period, approximately four similarly-sized objects hit the moon….

 : http://www.nasa.gov/home/hqnews/2012/apr/HQ12-135_Asteroid_Imapcts_Earth_Rocks.html

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