Determining the existence of a civilization on Earth that predates humanity is a perplexing question that has captivated the attention of many scientists and archaeologists.
An astrophysicist named Adam Frank often contemplates this question: After mastering interstellar travel technology, humanity will undoubtedly seek out other civilizations in the universe. However, the age of the universe is so vast that once humans discover a suitable planet for survival, any civilization that may have existed there could have long since vanished. In such cases, is there any way to determine whether an advanced civilization existed on this planet?
Frank approached his friend Schmidt, a scientist working at NASA, to pose this question. Schmidt found the question intriguing yet simultaneously difficult to answer because other planets are extremely distant, and we do not know what their physical environments are like. Ultimately, Schmidt simplified the issue and reframed it as: If an industrial civilization once existed on Earth, could we infer their existence?
Adam Frank is an American physicist, astronomer, and writer. His scientific research focuses on computational astrophysics, emphasizing star formation and the late stages of stellar evolution. Currently, his work includes studies on exoplanet atmospheres and astrobiology.
This question may seem nonsensical because if there were another industrial civilization that once existed on Earth, we would surely have unearthed what they created. Don’t archaeologists often discover tools made by humans from thousands of years ago? We can learn about the existence of these ancient civilizations through those tools.
However, do not forget that Earth is 4.6 billion years old, while the history of human civilization spans just under 10,000 years. Therefore, it is entirely possible that a civilization before us existed 10 million, 100 million, or even 1 billion years ago.
A span of thousands of years is relatively ancient for humans, but in reality, it is just a moment in Earth’s timeline. Over the course of 100 million years, mountains, rivers, and even the positions of continental plates on Earth undergo dramatic changes. Any creations by humans from long ago would certainly turn to dust after enduring 100 million years of significant geological change.
What about fossils? Aren’t we aware of the existence of dinosaurs through fossils? Many fossils dating back millions of years can still be found, so fossils left by organisms from previous civilizations should certainly be discovered?
It is entirely possible that a civilization before us existed 10 million, 100 million years ago… (Illustrative image).
What many people do not realize is that not all organisms have the opportunity to leave fossils after they die. Only a very small percentage of organisms can become fossils under specific conditions. Dinosaurs dominated Earth for 150 million years. During this time, countless dinosaur species roamed the planet. However, only a few thousand complete dinosaur fossils have been discovered worldwide.
In other words, on average, only one dinosaur fossil becomes a fossil and is eventually discovered by humans after tens of thousands of years. The written history of civilization spans only a few thousand years, and the history of industrial civilization is just over two hundred years. If a civilization vanished after thousands of years of industrialization, they likely left no fossil evidence behind.
Moreover, even if we find fossils of intelligent beings from a previous civilization, how can we evaluate them as intelligent beings when we only have fossils and no artificial tools?
According to the arguments made by the two scientists, we cannot know whether a civilization existed on Earth millions of years before humanity through direct evidence such as artifacts and artificial fossils. To answer this question, we must change our way of thinking. What we need to search for are traces of civilization that may still be detectable after tens of millions or hundreds of millions of years.
In the over two hundred years since the Industrial Revolution, humanity has burned a vast amount of fossil energy, leading to two consequences. First, a large amount of carbon dioxide produced from burning fossil fuels has entered the atmosphere, causing the average temperature of Earth 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 will reduce the C13 ratio in the atmosphere.
Any creations by humans from long ago would certainly turn to dust after enduring 100 million years of significant geological change. (Illustrative image).
Modern scientists have developed methods to measure Earth’s temperature changes over the past few billion years. If there was once an industrial civilization that widely used fossil energy, theoretically, we could infer their existence by observing temperature changes in Earth’s history.
For example, 56 million years ago, Earth experienced a dramatic temperature increase known as the Paleocene-Eocene Thermal Maximum. Over approximately 100,000 years, Earth’s average temperature rose by 5 to 8 degrees, while a large amount of carbon dioxide was released into the atmosphere, causing C13 levels to drop. This is very similar to the impact that our industrial civilization has had on Earth.
So, if millions of years after humanity’s civilization has perished, a new civilization arises on Earth, could they discover us?
For civilizations on Earth, the best place to find evidence of the existence of previous civilizations is not on Earth but on the Moon. This is because the Moon does not experience intense geological movements and is not subject to weathering caused by the atmosphere. The lunar landing craft created by humans could remain intact here for at least several million years.
If one day humanity unfortunately faces extinction, then tens of millions of years later, a new civilization will arise on Earth. After landing on the Moon, they might find a lunar rover left behind by humans. At that point, they will know we were here before them.
