In a recent work, Gavin Schmidt of NASA's Goddard Institute for Space Studies and Adam Frank of the University of Rochester ask a provocative question: Could there have been an industrial civilization on Earth millions of years ago? And if so, what evidence could we find today?
The authors first considered what signs of industrial civilization might be expected in the geological record. In our time, plastics, synthetic pollutants, elevated metal concentrations, and the detection of large-scale energy consumption, such as carbon-based fossil fuels. Collectively, they mark what some scientists call the Anthropocene era, where humans have a significant and measurable impact on our planet. However, the authors conclude that after ten million years it would be very difficult to distinguish these industrial by-products from the natural background. Even plastic, which used to be considered rather resistant, can be broken down relatively quickly by enzymes. Only radiation from nuclear power plants ̵
This thought experiment is not outlandish. In our book The Cosmic Zoo: Complex Life on Many Worlds William Bains and I devoted a whole section of the question to the question. Think about it: Intelligent dinosaurs like the Troodons existed in the Cretaceous, more than 65 million years ago. If it is confirmed that they have brains of the bird type – where the neurons are much more compact than in our brains – they would be pretty intelligent, much smarter than we thought. Maybe some of them build cities or fly around the world or pump oil. Maybe even a heroic dinosaur has landed on the moon. Okay, that seems unlikely, because we've already seen the artifacts. But even if we exclude space travel, how advanced could such a civilization have become?
Of course this raises a deeper question. There should have been enough time for dinosaurs to get smart enough to launch spaceships. Why do not you have them? Why have not octopuses, dolphins and some birds developed intelligence long ago? Kangaroos, for example, are tall, social, have manipulative hands, and are reasonably intelligent. Why did not they get any further? What is special about us humans?
Speculation about past civilizations is not only important to Earth, but also to other planets and moons. Eventually we can find the remnants of a civilization that no longer exists on an exoplanet, if we can recognize the signs. It is expected that the early TESS mission will discover thousands of new exoplanets, many of which are near Earth and relatively close to us (within about 50 light years). Some of those we might even visit and explore in the not-too-distant future.
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