Could an advanced civilization have existed on Earth before us?

A new scientific paper explores the provocative question of whether an advanced industrial civilization could have existed on Earth millions of years before humans and left traces that we might still detect today. The study, led by Gavin Schmidt of NASA's Goddard Institute for Space Studies and Adam Frank of the University of Rochester, examines what geological and chemical signatures such a civilization would produce and whether those signals could survive deep time.

The researchers focus on the Anthropocene, the current geological epoch defined by human impact, as a model. They consider markers like synthetic pollutants, plastics, and altered carbon and oxygen isotope ratios. However, they note that the geological record is incomplete: only a small fraction of Earth's surface is preserved in rocks older than a few million years, and plate tectonics continuously recycles the crust. For a civilization lasting only a few hundred thousand years—a blink in geological terms—the chances of leaving detectable evidence are slim.

Why this matters is that it challenges assumptions about the uniqueness of human civilization and the search for extraterrestrial intelligence. If we could miss an entire industrial era on our own planet, the search for technosignatures on other worlds may be far more difficult than previously thought. The paper, published in the International Journal of Astrobiology, does not claim such a civilization existed; rather, it asks what evidence we should look for.

Specific numbers and dates are not provided in the source, but the researchers point to the Anthropocene as a reference for human impact. They also note that the oldest known rocks are about 4 billion years old, but the continuous rock record only goes back about 600 million years. Background includes the fact that previous studies have considered dinosaur civilizations, but this paper is the first to seriously examine the detectability of an industrial civilization in deep time.

Next steps, according to the source, include further modeling of long-term signal preservation and collaboration with paleontologists and geologists to refine the search criteria. The authors emphasize that the exercise is valuable for refining methods to detect extraterrestrial civilizations, even if no such Earthly predecessor ever existed.