What if Humans Are NOT Earth's First Civilization? | Silurian Hypothesis

Thanks to Novium for supporting PBS. We are almost certainly the

first

technological

civilization

on Earth. But

what

if we are not? We are not. But how safe are we really? A favorite way to estimate the abundance of life in the universe is the famous Drake equation, which calculates that the number of intelligent extraterrestrial

civilization

s in our own galaxy that could overlap with us can be estimated by multiplying a chain of factors, basically summarized as the number of habitable planets multiplied by the probability of a planet forming life, then technological life, and then taking into account how long that civilization survives.

We now know that there are billions of habitable planets in our galaxy, but the other parameters remain extremely difficult to guess. And that is because we only have one example of the formation of life and civilization to develop. And we have no examples of technological species that have gone extinct, although we are on our way to getting at least one of them. If we detect just one more instance of life or technology, we can immediately improve our guess about the likelihood of a given planet reaching that stage of development. But do you know

what

would increase the probability even more?

If we saw it happen twice on the same planet. There is extremely vague evidence, not even evidence, perhaps just a "teaser", that life may have begun independently twice on Earth. There is a zircon crystal found in Western Australia that contains a small particle of carbon that appears to be filtered through a living metabolism. It has the characteristically higher proportion of carbon-12 versus carbon-13 that plants exhale. That speck of "biogenic" carbon was probably perfectly sealed in a zircon crystal probably about 4.1 billion years ago, dating back to before the Earth's crust was likely reliquefied by a massive asteroid bombardment that should have extinguished all life.

That's a long shot, but it's crazy given that the next oldest fossils (in Australia and also Greenland) date back to between 3.5 and 3.8 billion years ago, after the Earth solidified again after being hit. If so, then abiogenesis (life arising from non-life) would have to have occurred again. And that would mean that life actually begins very quickly if the right conditions are met. We would have to update our Drake equation estimate of the probability of life forming on a suitable planet. But this is all extremely speculative, and one of the reasons is that it's really difficult to verify the origin of life because these fossils are extremely rare.

Greenland and that part of Western Australia are the only fragments of land still left on the surface from that time. The rest of the entire crust has been subducted (returned to the Earth's mantle by tectonic activity) not once but many times. The crust is recycled approximately every half a billion years, meaning that much of the early fossil record has been removed, making it extraordinarily difficult to trace the early emergence of life. But if the geological record is so bad, then in 500 million years Earth's new inhabitants will have very little evidence that we ever existed. So could we even know that we are the

first

technological civilization on Earth?

And if we are not the first, that would also have huge implications for our Drake equation, forcing us to update both the probabilities of technological civilizations emerging from life and also our estimates of the life expectancy of those civilizations. I know this sounds like lizard-Illuminati nonsense, but one effort to properly address a proposal like this is a paper by NASA climatologist Gavin Schmidt and physicist and astronomer Adam Frank from a few years ago. They propose the Silurian

hypothesis

, which asks whether pre-human industrial civilizations could have existed. The name is a reference to old school Doctor Who.

I'll let you Google it to see what we're really looking for. Let me be very serious for a moment: I do not believe that such a civilization existed. Schmidt and Frank do not believe that such a civilization existed. The burden of proof for such a claim is enormous, and falls enormously on the plaintiff, and there is currently no real evidence. The real purpose of this video and the Silurian

hypothesis

is to formulate a very clear scientific question around a very speculative idea. So let's do just that. Broadly speaking, that question would be: Could a non-human industrial civilization have existed before us, even given our current lack of evidence for it?

And if so, how long would it have to have existed for it to be completely erased? And finally, what traces of it might still exist and what could we look for now? But first, to start thinking about the evidence that a past civilization may have left behind, let's think about what our civilization will be like in the distant future. Our species has existed for approximately 300 thousand years, but has only had a major impact during the last 10 thousand years of the Anthropocene era; by definition, it is called the era of our greatest impact. And that impact has accelerated enormously in the 300 years of the post-industrial revolution.

When you look at the world now, you might think that our buildings are the most telling signs of our presence once we are gone. But that won't be the case for long. The pyramids may have lasted for millennia, but they will not last for millions of years. All our great cities will erode to dust, be covered over or razed or end up in deserts, then ocean floors, then deep sedimentary layers, then mountains, then deserts again. Much of it will also be carried away by moving tectonic plates: subducted. It will become new rock in the mantle; its geological memory will be almost completely erased before it reappears, if it ever does.

So will any signs of these works be evident in the distant future? Mantle recycling means that anything older than 500 million years has virtually disappeared. But we do find many fossilized dinosaur bones that are hundreds of millions of years old. Surely we would find remains of a civilization that is only millions of years old. But that is not necessarily the case, due to the potentially limited extent of civilization, both spatially and temporally. Of course, we have obtained samples of the Earth's surface from many millions of years ago. Some of those areas are still exposed, but most are reached by excavating or drilling.

But here's the thing: we've accessed only a tiny fraction of a percent of Earth's original surface before the Quaternary period, 2.6 million years ago. And modern urban land cover today is less than 1% of the Earth's surface. So if a civilization like ours existed a few million years ago, it is extremely unlikely that we would have come across its physical remains today. That includes cities and artifacts, but also fossils. The rate of fossilization is so low that we have only discovered a small fraction of the species that once existed. Remember that dinosaurs roamed the Earth approximately 240 to 65 million years ago.

They have been absent a third of the time they were present. And over those 180 million years we have only a handful of specimens. By comparison, our 10,000 years of civilization are barely a blip in the fossil record, and our industrial age not even a blip in the fossil record. We can find T-rex, but we can't find T-rex from a few centuries in particular. I will explain in more detail the magnitude of Anthropocene climate change: Our best way to track geological time is in sedimentary rocks. This is a rock that was originally formed from the precipitation of dead ocean things on the ocean floor, accumulating over millions of years.

From sedimentary rocks that have since been exposed, or from deep cores drilled into the oceans, we can analyze these layers to track changes in the ocean chemistry, temperature, and biological content of these layers, which in turn reflect those same properties on a global scale. . The entire Anthropocene will be represented by a layer only a few centimeters thick in kilometers of sedimentary layers, of which the industrial era will be a proportionally small fraction (perhaps millimeters at best). Although a civilization in the distant future would probably not find our bones or artifacts, it could find and recognize this thin layer in the geological record.

As our structures and cities grew, so did our broader footprint. “Anthropocene” is the word for the geological era dominated by human activity. It's not a textbook yet, but it probably will be soon. Geological eras are periods of time reflected by distinct changes in the geological record. The Anthropocene certainly qualifies. In fact, the geologic marker that is currently being deposited in new sedimentary layers due to our activities bears an uncanny resemblance to some of the transitions in the geologic record from millions of years ago. So, to evaluate whether any of those previous events could be related to industrial activity, let's take a look at the details of how we are going to confuse future geologists and paleontologists with the garbage we are spreading on the Earth's surface and that are It has already been seen in newly deposited sedimentary layers.

First, there are the more direct chemical and isotopic imbalances that result from us making a lot of weird stuff. Industrial pollutants such as heavy metals and chemicals such as CFCs and their long-lived byproducts. Consumer waste such as rare

earth

s and plastics. Nitrogen fertilizers and even steroids from large-scale agriculture. Radioactive isotopes deposited globally from nuclear weapons tests lasting tens of millions of years. Then there is the effect of habitat destruction and species extinction, which will not be so much a distinct layer in the geological record as a sudden drop in biodiversity markers. But our main geological impact is, of course, climate change.

Remember that speck of biogenic carbon in the Australian glass? This is more than a specification. During the industrial revolution, about half a billion tons of carbon rich in the C-12 isotope have been pumped into the air. This is increasing the ratio of C-12 to C-13 in the atmosphere, which is then reflected in the soil and oceans and ultimately in the sedimentary layers that are currently forming. The temperature increase associated with this new atmospheric carbon will influence the geological record in several ways. Increased rainfall and rising sea levels further increase erosion. Warmer oceans release more dissolved CO2, which increases their acidity;

This and the change in temperature itself alter the fauna that can live in it and, ultimately, settle at the bottom of the ocean. There are many other known and unknown effects beyond these. So from all this it seems that it will be easy for a future civilization to see where we scribble “we were here” in the geological record. And if so, we should be able to find an earlier one. Except many of these signals can be duplicated by natural phenomena. We'll return to those natural explanations, but first let's see if there are any interesting past geologic markers that look anything like the one we're currently forging.

Let's go look for pre-human technological civilizations. Our geological record contains several candidates for “strange layers” that also represent massive environmental changes. Some we understand well, like the Cretaceous-Paleogene boundary, which is connected to a dinosaur-hating asteroid hitting Earth. But some still don't have widely accepted explanations. And here we come to the Silurian hypothesis, which asks whether any of these still-unexplained abrupt changes in the geological record could have been due to an industrial civilization. Schmidt and Frank focus on two broad types, which overlap a lot. We have hyperthermals, largely in the Eocene, 56 to 34 million years ago. These are characterized by rapid increases in global temperatures and are often accompanied by significant changes in carbon isotope ratios.

The latter suggests that the temperature change is due to a rapid injection of CO2 from the burning of some organic fuel. We're causing a hyperthermia now, but could some of the past hyperthermias also have been caused by something like us? It's not impossible, but prepare for debunking. Then we have the anoxic events in the oceans, some of which are found in the earlier Cretaceous and Jurassic periods. These are characterized by a rapid drop in ocean oxygenation, accompanied by a major extinction of marine life.We are seeing the beginning of a potential “OAE” right now. As in our case, ancient OAEs are usually accompanied by changes in CO2 isotopic ratios, so they could also have been caused by climate change.

If we go back further, there have been several abrupt changes since about 500 million years ago that involve combinations of the signals I have already described. And the further back we go, the harder it is to pinpoint the definitive cause, so there is more and more room for our fantasies about dinosaur empires. The biggest challenge in evaluating the Silurian hypothesis is that natural climate changes can duplicate many of today's anthropogenic signals, from changes in temperature and carbon status to different types of minerals being deposited on the ocean floor due to to changes in ocean life. . And there are many potential natural causes for climate change; for example, the periodic changes in the Earth's orbit characterized by Milankovic cycles, which we once covered and which are correlated with past climate changes.

And if a signal is not caused by climate change itself, then it could share a cause with that climate change. Spikes in heavy metals or rare

earth

elements can come from manufacturing technology or be produced by volcanic eruptions that spew large amounts of minerals and metals into the atmosphere and oceans. The radioactive isotopes could be due to a nuclear program or a nearby supernova explosion. Layers of soot and particles in the sediments could indicate combustion processes from an ancient industry, or come from widespread forest fires or an asteroid impact. These can send soot and dust into the upper atmosphere and eventually settle around the world.

And, more importantly, it can cause a change in climate if enough CO2 is released. There is good evidence that the Paleocene-Eocene Thermal Maximum, the first and largest hyperthermal maximum of the Eocene, was caused by a zone of giant magma that invaded a giant bed of fossil fuels. And these kinds of catastrophes and associated climate change can also trigger the kind of mass extinction that we hope will accompany our own geological end. That said, there are some things we are doing to our own geological layer that would be difficult to explain naturally. Some of the long-lasting synthetic chemicals actually have no known natural source, like some of these industrial fluorides.

There are things like the chirality of molecules – the left- or right-handedness of their symmetry – which is strongly unidirectional in nature, but random in our industrial production. I should also note that the sudden climate changes of the past appear to have been significantly less sudden than ours. So if we find a change that occurred on a time scale of centuries rather than tens of thousands of years, that could be an indication. But it's extremely difficult to get that kind of temporal resolution in the geologic record. Overall, this points to a kind of paradox: a civilization that perished due to climate change would leave a record so narrow that it could be invisible.

On the other hand, an advanced civilization that lives much longer, and is therefore presumably environmentally sustainable, could produce minimal ecological alteration for millennia and would therefore be almost invisible. In any case, distinguishing between these artificial and natural settings requires extremely careful analysis of the context, distribution and composition of these markers and their association with each other, while gathering clues that could span geological epochs. So have we detected signs of industry in ancient geological transitions? No. But our search has also been limited. And this is the true value of the Silurian hypothesis, as Schmidt and Frank themselves emphasize.

This is not about proposing prehuman industrial civilizations as a likely explanation for past geological events, but rather about refining our understanding of what to look for if we wanted to find evidence of it. And although it seems extraordinarily unlikely, it would be impossible to overstate the implications of discovering such a prehuman civilization. Both for our sense of our own place on this planet and for our understanding of the likely abundance of civilization in the universe. It can even guide us in the search for past life, even past civilizations on other worlds, starting with Mars. But most importantly, discovering an extinct people that reached the same or greater level of advancement as us would give us a new and impressive perspective on our own future and a profound reminder of our fragility.

Perhaps it is enough of a reminder to allow us to avoid the fate of that hypothetical predecessor and avoid becoming another local geological problem that had once dreamed of exploring all of space-time. Thanks to Novium for supporting PBS. Inspired by space, Novium Hoverpen 2.0: Interstellar Edition is a high-end pen designed to defy gravity at an angle of 23.5 degrees to be a subtle reminder of the axial tilt of our home planet. Whether writing physics formulas or taking notes on your favorite show, the Hoverpen is available in Starlight Silver, Mars Magma, and Neptune Blue. But if you choose Space Black, you can also have a hoverpen containing a piece of the Muonionalusta meteorite, which landed in northern Scandinavia over a million years ago.

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