A just published article states that the Earth had 70 asteroid impact hits on the level o,f or even larger than, the dinosaur killing impact event 65 million years ago. This is a significant increase in the number of "mega-hits" the Earth was thought to have endured 1.8 to 3.8 billion years ago. The Moon is thought to have been hit 4 times with the same size impactors.
The research was based on findings in Australian rock samples and computer studies. As stated by NASA:
"Evidence for these impacts on Earth comes from thin rock layers that contain debris of nearly spherical, sand-sized droplets called spherules. These millimeter-scale clues were formerly molten droplets ejected into space within the huge plumes created by mega-impacts on Earth. The hardened droplets then fell back to Earth, creating thin but widespread sedimentary layers known as spherule beds.
The new findings are published today in the journal Nature."
“The beds speak to an intense period of bombardment of Earth,” said William Bottke principal investigator of the impact study team at the Southwest Research Institute (SwRI) in Boulder, Colo. “Their source long has been a mystery.”
Read More About It: http://lunarscience.nasa.gov/articles/nlsi-scientists-find-history-of-asteroid-impacts-in-earth-rocks/
Sky Guy in VA