Some time ago I read about 3 major precambrian impact events. This site lists major North American impact craters including the giant Sudbury, which was originally 250 K in diameter and occurred about 1.8 billion ya...Thanks g!
great link, thanks, went to the Main Menu and found this one on Mars:
http://www.thelivingmoon.com/43ancients/04images/Mars2/Open_Pit01_sm.png
Reminds me of the Silverpit Impact Crater in the North Sea, discovered in 2002 by oil geologists:
http://news.bbc.co.uk/media/images/38168000/jpg/_38168726_crater150.jpg
http://news.bbc.co.uk/2/hi/science/nature/2164058.stm
But back to the article...”Much of the basins are composed of sediments that cannot be dated using any method. But Meert said the sediment also contains zircon, which can be dated using laser mass spectrometry – ...”
Question: And dating the zircon proves what?
