The Silurian Hypothesis - Ancient Civilization on Earth

If intelligent life existed elsewhere in the universe, how would we know? This was the question which astrophysicist Adam Frank had made a career trying to answer. In early 2017, Frank came up with a groundbreaking idea. Was it possible, he wondered, that any advanced industrial civilization which arose on any planet would trigger a planetary climate shift, much as humans have done on Earth? If so, Frank realized, finding evidence of quick temperature rises on other planets might be the first step in finding evidence of intelligent life. Seeking to explore the possibility further, Frank took his idea to NASA and its prestigious Goddard Institute for Space Studies, where, in short order, he found himself in the office of the Institute's director, Gavin Schmidt. He began to present his idea, but just as he was building momentum, Schmidt suddenly interrupted. Wait a second, Schmidt said. How do you know we're the only time there's been a civilization on our own planet? The question stopped Frank in his tracks. I felt a kind of temporal vertigo, he recalled, as the implication of the question dawned on him. Modern human beings have been around for about 300,000 years, with an advanced industrial civilization arising in only the past 300 years. Yet, complex life has existed on Earth for 400 million years. In other words, there has certainly been more than enough time for the rise and fall of one or more advanced civilizations in the Earth's history before humanity. What Schmidt was saying was that, if Frank was proposing a way to look for ancient evidence of intelligent life on distant planets, why not apply this idea to our own planet? This sent Frank's mind racing. Here was the director of a prestigious NASA institute, suggesting that an advanced industrial civilization, intelligent life, so to speak, could have existed on Earth many millions of years before human beings ever showed up. Was this possible? 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I have it on all my devices, and the best part is, I can use it on up to 5 devices simultaneously. Protect yourself and your family by visiting expressvpn.com forward slash universe inside you and arm yourself with an extra 3 months of ExpressVPN for free. It might seem like it would be easy to tell if an advanced civilization had existed on Earth in the past. Presumably, all we would have to do is look for the same type of physical evidence which has been discovered from more recent ancient civilizations. Evidence of buildings and roads, fragments of art, or written works. That is to say, we would uncover evidence of an advanced civilization millions of years in the past, much the same way as we did for, say, the ancient Egyptians or Aztecs. But in fact, it's not that simple. The problem is that the Earth's geological record does not go back past what is called the Quaternary Period some 2.6 million years ago. Go back further than that and everything has been turned over and crushed to dust. If an advanced civilization did exist millions of years in the past, we would not find evidence of their cities and roads and culture which have long since been returned to the Earth. But what about fossils? It might seem that surely an advanced ancient civilization would leave evidence of their existence in the fossil record. In reality, this is not necessarily true. Just think about dinosaurs who existed on Earth for 165 million years. To this day, only a few thousand full dinosaur specimens have been found, as in, less than 20 for every million years the dinosaurs existed. Consider humanity's current industrial civilization, which has arisen in only the last 300 years. Even if this industrial civilization lasts for another million years, it would still only be a fraction of the length of time dinosaurs existed. In other words, it is unlikely that in the long run, our own advanced industrial civilization is going to show up in the fossil record at all. The same would likely be true for an advanced industrial civilization which existed millions of years in the past. Frank and Schmidt knew that evidence of an advanced civilization on Earth millions of years in the past would not come through this type of direct evidence. They would not be hunting for ancient ruins or fossils. So what type of evidence, they asked, would exist? As Frank later described, the two men realized that the best way to answer this question is to figure out what evidence we'd leave behind if human civilization collapsed at its current stage of development. Simply, once a civilization reaches truly planetary scales, there has to be some feedback on the coupled planetary systems that gave it life, indelible footprints left on the planet's ecosystems, its air, water, rock, its climate. It was these footprints which Frank and Schmidt believed would be the key to finding an advanced ancient civilization. In 2018, the two men published a paper in the International Journal of Astrobiology which laid out in detail the various geological footprints they believed could serve as evidence of an advanced industrial civilization in the Earth's past. The paper caused an uproar in the scientific world, raising not only the mind-blowing possibility of an advanced civilization in Earth's past, but asking difficult questions about the impacts of our own advanced civilization on the planet. They called their theory the Silurian Hypothesis. To start, Frank and Schmidt thought about the type of agriculture necessary to feed the planet's nearly 8 billion people. To produce food on this scale, our industrial civilization has discovered ways to artificially fix nitrogen, breaking down the chemical bonds which hold nitrogen atoms together in the atmosphere to create biologically useful molecules which are used as fertilizers. Our large scale fertilizer use in agriculture is already changing the planet's nitrogen flows in a way that is detectable in the Earth's sediments. Similar evidence of changes in the Earth's nitrogen flows in the past, Frank and Schmidt proposed, could be one piece of evidence indicating the existence of an advanced industrial civilization. Next, they considered plastics, which over the past 75 years humans have been dumping into the ocean in enormous quantities. Over time, this plastic is ground down and eroded by the wind, sun, and waves, creating microscopic plastic particles which eventually sink to the ocean floor. Already, after less than a century, studies show this plastic marine litter forming a layer on the seafloor in coastal areas, deep basins, and even the Arctic. A similar layer now buried beneath the ocean floor might indicate an advanced civilization in the past. Going further, Frank and Schmidt realized that plastics are not the only human-made elements we're leaving behind. There are the rare earth elements used in modern electronics which have been extracted from hidden pockets within the Earth and spread all over the globe. There are non-naturally occurring chemicals that we manufacture industrially, which are already appearing in the Earth's sediments. There are even the radioactive isotopes related to nuclear activity. Plutonium-244, for example, has a half-life of 80.8 million years, meaning if an advanced ancient civilization conducted nuclear activity on a wide scale, it may show up in the record today. It was not just what we are leaving behind, which Frank and Schmidt considered, but how we are physically changing the Earth. Large-scale agriculture and mass deforestation have led to increased soil erosion all over the world, while rising sea levels cause further erosion in coastal areas, and rising temperatures in the polar regions increase erosion by melting ice and thawing permafrost. These human-made changes in the Earth's sedimentological records may show up deep in the future, or from deep in the past. Yet, for Frank and Schmidt, all of these factors together paled in significance to another factor, the one which had started them on the road to their Silurian hypothesis in the first place. Simply, if you're going to have an advanced industrial civilization, you've got to power it. Since the mid-18th century, humans have powered their civilization by burning fossil fuels, and the impacts this has had on the planet are significant. When fossil fuels get burned, the ratio of carbon-12 to carbon-13 usually found in the Earth's atmosphere, oceans, and soils is altered. Already, humanity's use of fossil fuels has changed this ratio significantly, in a way which will show up in the Earth's geological record. According to Frank and Schmidt, a similarly dramatic change in the Earth's carbon ratio deep in the past might suggest that somebody else was burning fossil fuels. There is also the issue of temperature. Humanity's industrialization has been accompanied by a warming of about 1.8 degrees Fahrenheit since the 18th century, with more substantial rises projected in the future. In the long term, a global temperature spike will be detectable in geological records contained within oceans, rock, plants, and ice. Adam Frank had started with the idea that evidence of a climate shift on a distant planet might be evidence of intelligent life sometime deep in the past. In bringing this idea to Gavin Schmidt, the two men had come up with something even more incredible, that perhaps similar evidence might exist on our own planet. Looking at the potential evidence they had compiled, Frank asked, if these are the traces our civilization is bound to leave for the future, might the same signals exist right now in rocks just waiting to tell us of civilizations long gone? It is important to mention that both Frank and Schmidt outwardly believed the answer to this question was no. Within their Silurian hypothesis, they explicitly stated, we strongly doubt that any previous industrial civilization existed before our own. And when the paper was published, Frank bluntly told the Washington Post, I don't believe an industrial civilization existed on Earth before our own. I don't think there was a dinosaur civilization or a giant tree sloth civilization. In fact, Frank and Schmidt devoted much of the space within the paper to poking holes in their own theory. They admitted that much of the potential evidence they were talking about may not be unique to human activity, even if it was discovered. Dramatic spikes and changes in the Earth's geological record can result from things like meteor strikes and volcanic eruptions or any number of other factors. Moreover, they recognized that the specific markers they were talking about as potential evidence, things like fertilizers, plastics, chemicals, and fossil fuels, represented a very specific path to advancement taken by human beings. If another advanced civilization had arisen in the past, there would be no guarantee it would have developed in the same way. Additionally, if there was an advanced industrial civilization in the past, it might be expected that