Can technologically advanced civilizations develop underwater?

Thought Experiment: Were There Civilizations Before Humanity?

Two-legged dinosaurs that built a global technical civilization, ruled the planet for a geological blink of an eye, and then vanished again - would we know about them? And how can we find them? That is surprisingly difficult to answer, write Gavin A. Schmidt, Director of the Goddard Institute for Space Studies at NASA, and Adam Frank from the University of Rochester. In their new publication, which has now been accepted for publication by the International Journal of Astrobiology, they conclude that the history of the earth itself can hide a civilization like humanity. The two scientists concluded that if you didn't look for it, you might overlook the evidence to support it.

"This is a fascinating and important article," says paleobiologist Jan Zalasiewicz from the University of Leicester, who is also involved in the working group on the definition of the Anthropocene. "I hope that he will initiate further work on such questions." The background to the speculation about the forerunners of mankind is a topic that could hardly be more topical. Whether it concerns the protection of ecosystems, models of the future world climate or the search for civilizations in the distant universe - all these topics can be traced back to the question asked by Schmidt and Frank: How does a global technical civilization change the planet?

This article is featured in Spectrum Compact, Alien Life - Are We Alone in Space?

For the sake of the argument

Frank emphasizes in an article for "The Atlantic" that the authors do not believe that such a civilization really existed. The thought experiment is an "astrobiological perspective" on humanity and its traces in the rocks. In the long term, they are probably very tender. This would include, for example, significantly more sediment deposits due to erosion on land as well as accumulations of rare technical metals and radioactive elements in the deposits; but above all the changes in the carbon, nitrogen and energy cycles, which can leave clear signals in the form of drastic changes in the climate and ocean.

Schmidt and Frank list a number of rapid and catastrophic geological events, the effects of which in ancient rocks may have similarities with those of humanity. Among them is an abrupt heat wave 55 million years ago, which was triggered by enormous amounts of carbon dioxide and which experts are discussing as a possible model for man-made climate change. The authors argue that it is extremely difficult to separate the effects of a global civilization from the natural causes of such events.

They consider it extremely unlikely that they will actually find artifacts or even fossil remains of a civilization that is millions of years old - they refer to the Antikythera mechanism. This artifact is the only one of its kind left, although it is only a few thousand years old. How are such constructions supposed to survive the tens of millions of years that separate us from hypothetical non-human civilizations?

How to succumb to oblivion

Zalasiewicz again contradicts this assessment. “The paper describes chemical signals well, but it neglects the possibility that there could be very widespread technofossils in terrestrial and coastal layers.” So one can expect that, for example, mineral building materials such as brick, concrete or glass will change over millions of years, but would still clearly stand out as artificial. "A geologist of any species would very quickly recognize them as something extraordinary." A global civilization would also produce enormous amounts of such materials, he points out.