fabian s. klinkeWhat if Humans Are NOT Earth’s First Civilization? | Silurian Hypothesis
Source: What if Humans Are NOT Earth’s First Civilization? | Silurian Hypothesis, PBS Space Time, 20:13, uploaded 2023-12-07, category Education.
PBS Space Time begins with a confidence that quickly turns into a question. Humanity is almost certainly the first technological civilisation on Earth. The geological record seems to support that view, although the record itself survives only in fragments. A civilisation can disappear long before the planet stops carrying its effects.
The Drake equation and one example too few
The Drake equation estimates the number of intelligent civilisations in the Milky Way by multiplying factors such as the number of habitable planets, the chance that life forms, the chance that life becomes technological, and the length of time a technological civilisation survives. Astronomers now know that the galaxy contains billions of habitable planets. The other terms remain hard to estimate because Earth supplies our only example of life, civilisation, and technological extinction.
One additional example of life or technology would improve those estimates. A second beginning of life on the same planet would tell us more. The video treats a 4.1-billion-year-old zircon from Western Australia as a possible hint. A tiny carbon inclusion inside the crystal has a higher proportion of carbon-12 than carbon-13, a pattern associated with biological metabolism. If the inclusion really records life, it predates the asteroid bombardment that probably melted and sterilised Earth’s crust. The earliest accepted fossils in Australia and Greenland date from roughly 3.5 to 3.8 billion years ago, after the crust had solidified again. Abiogenesis, life arising from non-living matter, would then have happened twice.
The evidence remains extremely weak. The early fossil record survives in only small areas of Greenland and Western Australia because tectonic activity has pulled most of the ancient crust into the mantle. Earth recycles much of its crust over roughly half a billion years. That process removes evidence of early life and creates the first route into the Silurian hypothesis: if the geological record can erase the beginning of life, it might also erase a technological civilisation.
The question behind the Silurian hypothesis
Gavin Schmidt, a NASA climatologist, and Adam Frank, a physicist and astronomer, give this speculation a formal name in their paper, “The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?”. The name refers to an old Doctor Who story. The paper does not claim that an earlier civilisation existed, and the video makes the same distinction. Such a claim carries a heavy burden of proof, while current evidence supplies none.
The useful question has a narrower form. Could a non-human industrial civilisation have existed before us and left a record that geological processes have almost erased? How long ago would it need to have lived for its cities, artefacts, and bodies to vanish? Which traces would remain detectable now?
The video approaches those questions through our own future. Human beings have existed for roughly 300,000 years, while the Anthropocene marks the much shorter period in which human activity has become a major geological force. Industrialisation has accelerated that effect over about three centuries. Our buildings look like obvious evidence of civilisation because they dominate the present. They will not dominate the deep future.
The pyramids may last for thousands of years, although cities will erode, burn, sink, or become buried. Sediment can carry their remains from land to ocean floor, then into deeper rock. Tectonic plates can pull that rock into the mantle, where geological processes rework it and erase much of its history. Material older than half a billion years has little chance of returning in a recognisable form.
A civilisation occupies very little of the record
Dinosaur bones seem to challenge this account. Some dinosaurs lived hundreds of millions of years ago, and their fossils remain visible. The comparison breaks down when the scale and distribution of the evidence are examined. Scientists have sampled only a tiny fraction of the Earth’s surface from before the Quaternary period, which began 2.6 million years ago. Modern urban land covers less than one per cent of the planet. A civilisation that occupied a similar area a few million years ago could leave its physical remains outside every place we have examined.
Fossils also offer a poor census of past life. Dinosaurs lived from roughly 240 to 65 million years ago, yet only a small number of specimens represent those 175 million years. Human civilisation has occupied about 10,000 years, and the industrial era forms a thin interval within that span. Finding a dinosaur tells us that dinosaurs lived. It does not give us a record of every century in which a particular species existed. The trace of a short-lived civilisation could disappear even when the species that built it leaves other fossils.
Sedimentary rock gives a future geologist a better chance. Dead organisms and material from the oceans settle into layers that preserve changes in chemistry, temperature, and biological content. The entire Anthropocene may form a layer only several centimetres thick within kilometres of sediment. The industrial era could occupy a few millimetres. A future civilisation might miss our buildings and still recognise that thin layer as an abrupt change in the planet’s history.
The Anthropocene as a geological signature
Human industry has already placed several unusual signals into new sediment. Heavy metals and industrial chemicals can accumulate alongside rare earth elements, plastics, and nitrogen from large-scale agriculture. Long-lived radioactive isotopes from nuclear weapons testing will remain for tens of millions of years. Habitat destruction and extinctions will appear as a sudden fall in the markers of biodiversity.
Climate change supplies the largest signal. Industrial activity has released around half a trillion tonnes of carbon rich in carbon-12. That change in the ratio of carbon-12 to carbon-13 now appears in the atmosphere, soil, oceans, and sedimentary layers. Warmer oceans alter dissolved carbon dioxide, acidity, and the organisms that can live there. Rising seas and heavier rainfall increase erosion. The geological record will carry several effects from the same disturbance, although the video also points out that many of those effects have natural counterparts.
The search therefore turns to older abrupt changes. The Cretaceous–Paleogene boundary has a widely accepted explanation in an asteroid impact. Other transitions remain harder to explain. Schmidt and Frank focus on hyperthermals, rapid temperature increases found largely in the Eocene between 56 and 34 million years ago, and ocean anoxic events, in which oxygen levels fall across large parts of the ocean and marine life dies. Both types of event can include changes in carbon isotope ratios that resemble the effects of burning organic fuel. Earlier geological transitions, especially those more than 500 million years old, leave still more room for uncertainty because their causes are harder to identify.
Natural events can imitate industry
A geological marker becomes useful only when its full context separates artificial activity from natural change. Milankovitch cycles, which describe long-term changes in Earth’s orbit, correlate with past climate shifts. Volcanic eruptions can deposit heavy metals and rare earth elements without any technology. A nearby supernova can produce radioactive isotopes. Wildfires and asteroid impacts can leave soot and particles in sediments, while also changing climate through the release of carbon dioxide.
The Paleocene–Eocene Thermal Maximum, the first and largest Eocene hyperthermal, gives the video a strong natural counterexample. Evidence points towards a giant magma zone intruding into a fossil-fuel deposit as the source of the climate shift. The event can produce a combination of carbon, temperature, and extinction signals that resembles a technological catastrophe.
Some traces would be harder to explain through nature. Certain long-lived industrial fluorides have no known natural source. Industrial chemistry also produces a distinctive distribution of molecular chirality, the left- or right-handed form of a molecule, because manufacturing processes can favour patterns that natural chemistry does not. The speed of a change would help as well. Past climate shifts usually unfold over tens of thousands of years or longer, while industrial change has taken centuries. Geological dating rarely gives enough resolution to separate those timescales with confidence.
The paradox of visibility
The hypothesis contains a problem that runs in both directions. A civilisation that causes its own collapse through climate change could leave a short, narrow signal that disappears into the record. A long-lived civilisation that learns to limit its ecological effects could leave almost nothing distinctive after millions of years. Survival makes a civilisation less visible, while collapse can make its evidence too brief to find.
Distinguishing the two cases would require careful work on the distribution, composition, and timing of the markers, together with their relation to one another. The video reports that researchers have found no sign of an ancient industrial civilisation. The search has been limited, though, which is why the absence of a detection does not close the question.
The search method and the historical claim
The Silurian hypothesis works as a test of our search methods. Unexplained climate events serve as test cases. The hypothesis asks which chemical, isotopic, biological, and temporal combinations an industrial civilisation would leave behind, then asks whether those combinations can be separated from natural events.
Finding such a civilisation would change the Drake equation in both directions. It would show that technological intelligence can arise more than once on one planet, which would affect estimates of technological emergence. Its disappearance would also provide one example of a technological civilisation’s lifespan. The same search could guide the study of ancient life on Mars, where geological evidence has also been lost or altered over time.
The video closes with the scale of the possible discovery. An extinct civilisation that reached our level of technology, or went beyond it, would change how we understand Earth’s history and the chances of civilisation elsewhere. That implication remains hypothetical. The evidence supports a research question about the traces of industry. The existence of a prior civilisation remains unsupported.
Limits
This note reconstructs PBS Space Time’s argument from the complete English original caption track, the video metadata, and the description. The metadata supplies no chapters. The description links sponsor offers, PBS support, Patreon, merchandise, the mailing list, the Space Time search site, and end-credit music. It contains no link to the Silurian Hypothesis paper, so that reference is included because the video names it and the primary paper is available separately.
The zircon, fossil, crust-recycling, Anthropocene, hyperthermal, ocean-anoxic-event, isotope, and geological-timescale claims remain attached to the video’s presentation here. The video uses the zircon carbon inclusion as a possible clue and labels the evidence highly speculative. It also reports that no ancient industrial signature has been found. Those statements do not establish the underlying geological claims independently, and the absence of a search result cannot show that a prior civilisation never existed.