Determining the existence of a civilization on Earth that predated humans is a perplexing question that captures the interest of many scientists and archaeologists.
The Silurian Hypothesis: Looking for Industrial Footprints
Adam Frank, an astrophysicist, often ponders this question: After mastering interstellar travel, humans will undoubtedly seek out other civilizations in the universe. But the universe is so old that by the time humans find a suitable planet for survival, any civilization that once appeared there might have long vanished. In this scenario, how can we determine if an advanced civilization ever existed on that planet?
Frank approached his friend Schmidt, a scientist working at NASA, with this question. Schmidt found the question intriguing but
difficult to answer because other planets are very far away, and we don’t know their physical environments. Ultimately, Schmidt simplified the problem, turning it into the question: If an industrial civilization once existed on Earth, could we infer their existence?
This question might seem trivial, as surely, if another industrial civilization had existed on Earth, we would excavate their creations. Don’t archaeologists routinely find tools made by humans from thousands of years ago? We learn about the existence of these ancient civilizations from such tools.
However, let’s not forget that Earth is 4.6 billion years old, and the history of human civilization is less than 10,000 years. Therefore, it’s entirely possible that a civilization preceding us lived 10 million, 100 million, or even 1 billion years ago.
Thousands of years is a relatively ancient timeframe for humans, but in reality, it’s just a fleeting moment for Earth. On a scale of 100 million years, mountains, rivers, and even the positions of continental plates on Earth undergo dramatic, Earth-shattering changes. Any creations made by humans long ago would undoubtedly turn to dust after enduring 100 million years of intense geological change.
What about fossils? Don’t we know about the existence of dinosaurs through fossils? Many fossils dating back millions of years are still discoverable, so surely fossils left by intelligent beings from a previous civilization would also be found?
What many people don’t know is that not every organism gets the chance to leave behind a fossil after death. Only a very small percentage of organisms can become fossils under specific conditions. Dinosaurs dominated Earth for 150 million years. During this period, countless dinosaur species roamed the Earth. However, only a few thousand complete dinosaur fossils have been discovered worldwide.
In other words, on average, only one dinosaur carcass turns into a fossil and is eventually discovered by humans every tens of thousands of years. The history of human written civilization is only a few thousand years, and the history of industrial civilization is just over two hundred years. If a civilization disappeared after a thousand years of industrialization, it’s very likely they would leave no fossil evidence.
Furthermore, even if we found fossils of intelligent beings from a previous civilization, how could we determine they were intelligent if we only had fossils and no artificial tools?
The Clues Beyond Direct Remains
According to the two scientists’ arguments, we cannot learn about a civilization that existed on Earth millions of years before humans through direct evidence like artifacts and artificial fossils. To answer this question, we must change our thinking. What we need to look for are traces of a civilization that could still be detected after tens or hundreds of millions of years.
In the two hundred years following the Industrial Revolution, humans have burned a vast amount of fossil fuels, leading to two consequences. First, a large amount of carbon dioxide produced by burning fossil fuels entered the atmosphere, causing the Earth’s average temperature to rise. Second, the C13 isotope contained in fossil fuels is lower than the isotope in the atmosphere, so the widespread use of fossil energy would reduce the proportion of C13 in the atmosphere.
Modern scientists have developed methods to measure Earth’s temperature changes over the past few billion years. If an industrial civilization previously used fossil energy extensively, theoretically, we could infer their existence by observing temperature changes in Earth’s history.
For example, 56 million years ago, Earth experienced a sharp temperature increase known as the “Paleocene-Eocene Thermal Maximum.” Over about 100,000 years, Earth’s average temperature increased by 5 to 8 degrees, while a large amount of carbon dioxide was released into the atmosphere, causing a decrease in C13 content. This is very similar to the impact our human industrial civilization has had on Earth.
Our Legacy and the Moon
So, if millions of years after human civilization perishes, a new civilization forms on Earth, could they discover us?
For civilizations on Earth, the best place to find evidence of a previous civilization’s existence is not Earth itself, but the Moon. Because the Moon lacks violent geological movements and weathering caused by an atmosphere, human-made lunar landers could remain intact there for at least a few million years.
If, one day, human civilization unfortunately perishes, and tens of millions of years later, a new civilization emerges on Earth, after landing on the Moon, they might find a lunar rover left behind by humans. At that point, they would know that we were here before them.
