Curtis
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Another recent theory about snow ball earth maybe earth was covered by ice like Antarctica and it ground off much of the craters and mountains and volcano tops. from news page:[h=2]Serendipity in suspicious sediments[/h]The geochemical evidence is powerful, but chance discussions at a recent scientific conference made each future coauthor realize that there’s even more to the story.
For one thing, “around 600 to 700 million years ago, Earth loses its craters,” notes study coauthor Bill Bottke, a planetary scientist and asteroid expert at the Southwest Research Institute in Boulder, Colorado. Some ancient craters still exist on stable continental cores named cratons, but they are few and far between. (Recently, a city-size impact crater was found under the ice in Greenland.)
For one thing, “around 600 to 700 million years ago, Earth loses its craters,” notes study coauthor Bill Bottke, a planetary scientist and asteroid expert at the Southwest Research Institute in Boulder, Colorado. Some ancient craters still exist on stable continental cores named cratons, but they are few and far between. (Recently, a city-size impact crater was found under the ice in Greenland.)