How do we tell the difference between geologic ages? - Livescience.com

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How do we tell the difference between geologic ages?  Livescience.com
https://news.google.com/__i/rss/rd/articles/CBMiOmh0dHBzOi8vd3d3LmxpdmVzY2llbmNlLmNvbS93aHktZ2VvbG90aWMtdGltZS1wZXJpb2RzLmh0bWzSAT5odHRwczovL3d3dy5saXZlc2NpZW5jZS5jb20vYW1wL3doeS1nZW9sb3RpYy10aW1lLXBlcmlvZHMuaHRtbA?oc=5

2020-03-08 11:00:00Z
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