Perhaps at least 100 million years ago, another technological civilization evolved on earth and found 1 decent deposit of pure element 115 very early in their history. (hivelink)
Then perhaps this civilization learned to use element 115 for antigravity travel and even interstellar travel. It then expanded out without leaving much trace or evidence.
(hivelink)- Perhaps this non human civilization has been on earth for over 100million years but was forced to live underground when 65 million years ago a large explosion caused the earth temperatures to drop many degrees below their preferred. tid:3431 (1) (hivelink)
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