What if We Aren’t the First Advanced Civilization on Earth?

Earth scientists at the turn of the century, Gavin Schmidt among them, were enthralled by a 56-million-year-old segment of geologic history known as the Paleocene-Eocene Thermal Maximum (PETM). What most intrigued them was its resemblance to our own time: Carbon levels spiked, temperatures soared, ecosystems toppled. At professional workshops, experts tried to guess what natural processes could have triggered such severe global warming. At the dinner parties that followed, they indulged in less conventional speculation.

During one such affair, Schmidt, now the director of NASA’s Goddard Institute for Space Studies, couldn’t resist the comparison.

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