How Would We Know If Intelligent Life Existed on Earth Before Humans?

By Charles Q. Choi

Reptilian menaces called Silurians evolved on Earth before humankind — at least in the “Doctor Who” rendition of the universe. But science fiction aside, how would we know if some advanced civilization existed on our home planet millions of years before brainy humans showed up?

This is a serious question, and serious scientists are speculating about what traces these potential predecessors might have left behind. And they’re calling this possibility the Silurian hypothesis.

When it comes to the hunt for advanced extraterrestrial civilizations that might exist across the cosmos, one must reckon with the knowledge that the universe is about 13.8 billion years old. In contrast, complex life has existed on Earth’s surface for only about 400 million years, and humans have only developed industrial civilizations in the last 300 years. This raises the possibility that industrial civilizations might have been around long before human ones ever existed — not just around other stars, but even on Earth itself.

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