If another advanced civilization lived on Earth before us, would we know? - CNN

What the report says

CNN reports on the “Silurian hypothesis,” a 2018 thought experiment by University of Rochester astrobiologist Adam Frank and NASA scientist Gavin Schmidt that asks whether Earth’s geological record would reveal an advanced civilization that existed millions of years before humans. The idea emerged from a 2017 conversation in which Frank was considering whether alien civilizations might trigger climate change, and Schmidt challenged the assumption that Earth had never hosted an earlier technological society.

The scientists did not argue that such a civilization existed. Instead, CNN says their paper examined what kinds of evidence might survive if a society had used large amounts of energy, altered the climate and then disappeared. They considered how quickly cities and surface structures can vanish through erosion, tectonics and volcanism, and why fossils would be an incomplete guide. They also looked at chemical fingerprints in ancient sediments, including carbon shifts, persistent pollutants, plastics, artificial agricultural compounds and heavy metals that future geologists might associate with today’s human activity.

CNN places the discussion alongside known ancient climate disruptions, especially the Paleocene-Eocene Thermal Maximum about 55 million years ago, when temperatures rose sharply and ecosystems were stressed after a major carbon release. The article notes that scientists generally view such events as natural, though some causes remain debated.

The hypothesis remains speculative and contested. Geologist and paleontologist Jan Zalasiewicz told CNN the idea is thought-provoking but said a civilization resembling modern humanity would likely leave a strong technological and waste signature. Frank framed the value of the exercise as less about proving a lost civilization and more about asking whether energy-intensive societies can avoid destabilizing their own planetary systems.