The Swift Erosion of Historical Evidence

In terms of space, we have a strong basis for asserting that no other industrial civilization exists within our solar system, at least as far out as Pluto. This conclusion is supported by the substantial data acquired from various space probes sent to explore our celestial neighborhood.

While we can speculate about civilizations beyond Pluto, our knowledge is limited. The discovery of thousands of exoplanets in the last two decades, facilitated by the Kepler space telescope and advanced technologies, suggests that the Milky Way alone may contain over 10 billion potentially habitable planets. Yet, these distant worlds remain out of our reach, and our current technological means allow us only to identify certain atmospheric elements on nearby exoplanets. Although next-generation telescopes like the JWST and ELT may detect signs of atmospheric biomarkers, identifying evidence of an industrial civilization on planets situated tens or even hundreds of light-years away is, for now, a matter of science fiction. The only hope of overcoming this vast ignorance would be through the detection of intelligent signals, a pursuit that the SETI project has been engaged in for decades, albeit without success thus far.

Exploring the cosmic void for another industrial civilization is a daunting task. The challenge of investigating the abyss of time is equally formidable, particularly without leaving Earth. Fossil records indicate that complex life forms have been evolving on our planet for over 500 million years. Evolution is not a straightforward process; it is marked by sudden bursts of life and mass extinctions. Moreover, numerous 'technical' adaptations, such as vision and flight, have been independently developed by various species throughout history, responding to similar evolutionary pressures.

This raises an intriguing question: could there have been other intelligent species that existed on Earth in the distant past and developed an industrial civilization akin to ours? If such civilizations did exist, what geological traces would we need to search for to confirm their presence?

The quest to answer this second question guided the research of climatologist Gavin A. Schmidt and astrophysicist Adam Frank. Their findings were published in April 2018 in the International Journal of Astrobiology, under the title “The Silurian Hypothesis,” a reference to a storyline in the 1970s science fiction series Doctor Who, featuring intelligent reptiles, the Silurians, awakened by human nuclear experiments.

It is important to note that their research yielded negative results; Schmidt and Frank did not find geological evidence that would substantiate the existence of a past industrial civilization, nor do they believe such a civilization ever existed. Nonetheless, their reasoning offers valuable insights, particularly regarding the vastness of geological time and how swiftly the traces of a civilization like ours could be erased by the ongoing processes reshaping continents and ocean floors.

To grasp what remnants an ancient industrial civilization might have left behind, one must first consider what traces ours would leave if humanity were to suddenly vanish.

Curiously, if a nuclear conflict or natural disaster were to abruptly end human existence, archaeologists from a distant future might uncover no artifacts or even fossilized remains of our species.

Today, the structures of our industrial civilization—highways, railways, bridges, skyscrapers, megacities, dams—are monumental. Human activities have significantly altered the Earth's surface, producing visible effects from space, such as illuminated urban areas at night and agricultural fields marked by geometric patterns. However, the geological lifespan of these constructions is minuscule in comparison.

The Negev desert in Israel, the oldest large land area currently known, dates back about 1.8 million years. However, complex life has inhabited Earth for over 280 times that duration, burying remnants of its existence at depths in sites that remain largely unexplored. Should humanity vanish tomorrow, erosion and sedimentation would erase all evidence of our cities and artifacts within a couple of million years.

Considering that urbanized regions occupy less than 1% of the Earth's total surface, the likelihood of recovering remnants of our civilization in the distant future is extremely low. Additionally, fossilization is a rare occurrence influenced by numerous factors, such as climate and the ratio of soft to hard tissues in deceased organisms. For instance, despite the billions of dinosaurs that roamed Earth for roughly 200 million years, we possess nearly complete fossils of only a few thousand. This translates to only a handful of dinosaur fossils for every 100,000 years across countless species that existed during that time.

Consequently, the prospect of discovering evidence of an industrial civilization that existed millions of years ago, albeit for just a few thousand years, is minimal. Does this mean it is impossible to find traces of ancient industrial civilizations? Should we accept that we will leave no mark of our own existence? Not entirely. While artifacts may deteriorate swiftly and fossils are scarce, the global impact of industrial civilization on Earth's climate and mineralogy endures.

The Global Impact of Industrial Civilization in Anthropocene Sediments

Oceanic sediment cores dating back millions of years can be found across the globe. Typically, a few centimeters of sediment accumulate every thousand years. Within these layers, paleontologists of the future could uncover remnants of the Anthropocene, a geological epoch defined by the extensive influence of human activities over recent centuries. These activities can be tentatively reconstructed through the chemical compounds present in these sediments.

Future paleontologists examining the sediment from the Anthropocene would first notice a significant alteration in the ratio of carbon isotopes ¹³C and ¹²C. Since the late 18th century, humans have released over 500 billion tons of fossil carbon, previously trapped in coal, oil, and natural gas, into the atmosphere. Furthermore, industrial activities have led to extensive deforestation, releasing substantial amounts of carbon dioxide from biomass combustion.

All carbon from fossil fuels and deforestation originates biologically, resulting in a lower ¹³C content compared to the larger mass of inorganic carbon in nature. Thus, one consequence of industrial activity is the declining ratio of the ¹³C isotope compared to the ¹²C in the atmosphere, oceans, and soils, a phenomenon known as the Suess effect, which currently reflects a change of about 1‰ lower than in pre-industrial times.

The release of vast amounts of fossil carbon and greenhouse gases like methane and nitrous oxide has caused average global temperatures to rise by approximately 1 °C since the mid-19th century. Future paleontologists could detect these changes by analyzing the concentration of calcium carbonate in the foraminifera found in Anthropocene marine sediment layers. Increased calcium carbonate levels may indicate higher amounts of CO? dissolved in oceans, leading to surface water acidification.

Another significant change resulting from industrial civilization is the excessive nitrogen introduced into river systems from agricultural fertilizers. This influx of nitrogen promotes microbial growth in coastal ocean waters, depleting dissolved oxygen levels. This process gives rise to anoxic regions in oceans, resulting in the expansion of dead zones. These zones would be identifiable in Anthropocene sediments by their higher organic content and reduced bioturbation, or the alteration of deposits by living organisms.

Mining activities necessary to sustain industrial civilization have also resulted in increased concentrations of lead, chromium, antimony, rhenium, platinum, gold, and rare-earth elements in river waters, surpassing natural background levels. These elements will alter coastal sediment composition, revealing a distinct peak in concentration corresponding to the Anthropocene layer.

The distribution of fossils discovered by future paleontologists will also reflect the global impact of industrial civilization and human activities. The demographic success of our species over recent centuries has coincided with the proliferation of invasive small mammal species such as mice, rats, and cats, which have contributed to the decline of many native species. The extinction of megafauna in America and Australia at the end of the last ice age is another immediate geological consequence of human population growth. Thus, the extinction of various animal species alongside the dominance of a few others will characterize the fossil record of the Anthropocene, should it be studied by paleontologists from a potential future civilization.

Moreover, industrial chemical products that are resistant to degradation are now globally dispersed. Compounds like polychlorinated biphenyls (PCBs), chlorofluorocarbons (CFCs), and synthetic steroids, if found in contemporary sediments, could serve as definitive proof of an industrial civilization that synthesized them. However, the longevity of these compounds against degradation through chemical, photochemical, and biological processes remains uncertain. Plastics, on the other hand, have the potential to endure for extensive periods, particularly when embedded in highly resistant waste aggregates subjected to high temperatures, known as plastiglomerates.

Finally, the presence of transuranic radioactive elements cannot be overlooked. Should humanity face extinction via nuclear catastrophe, certain isotopes utilized in atomic weapon production have half-lives long enough to remain detectable after millions of years. Notably, plutonium-244 and curium-247 exhibit half-lives of 80.8 and 15 million years, respectively.

In conclusion, if our current industrial civilization were to vanish within a few centuries, the remnants of its activities and existence would likely be limited to the traces of planetary pollution found in the sediments of the Anthropocene. These markers would be characterized by:

• The release of vast quantities of biologically-derived carbon into the environment for energy production.
• The global increase in temperatures resulting from the greenhouse effect.
• Alterations to the nitrogen cycle.
• Ocean acidification and the emergence of dead zones due to oxygen depletion.
• The extinction of numerous animal species alongside the uncontrolled proliferation of a few.
• Peaks in the distribution of rare metals for industrial use and possibly isotopes of radioactive elements associated with atomic weaponry.
• Synthetic pollutants such as PCBs, CFCs, and plastics.

Do Geological Traces of Past Industrial Civilizations Exist?

If this inventory represents the entirety of what an industrial civilization like ours would leave behind in Quaternary Era sediments, then we can regard these traces as geological markers. Their presence raises the question of whether they indicate the passage of other industrial civilizations on Earth, created by non-human species that have since disappeared.

The Silurian hypothesis, central to Schmidt and Frank’s investigation, seeks geological evidence of events that transpired millions of years ago. Such occurrences bear characteristics similar to those that our industrial civilization could potentially imprint in Anthropocene sediments, yet cannot be directly linked to natural disasters like asteroid impacts or mega-volcanic eruptions.

The first event noted by Schmidt and Frank is the Paleocene-Eocene Thermal Maximum (PETM), which occurred approximately 56 million years ago. This event lasted between 100,000 and 200,000 years and was marked by an average temperature increase of 5 to 7 °C. In less than 5,000 years, a significant volume of carbon of unknown origin was released into the environment, producing a pronounced negative peak in the carbon isotope ratio similar to that observed today due to human industrial activities.

Following this, several other hyperthermic events occurred over the next six million years, collectively known as ELMO (Eocene Layers of Mysterious Origin). These events were characterized by global temperature increases, declines in carbon isotope ratios, and oceanic anoxia.

The Middle Eocene Climatic Optimum (MECO), marked by sudden temperature increases and shifts in carbon isotope ratios, dates back around 40 million years.

Additionally, numerous oceanic anoxia events (OAE) have been identified in geological sediments, occurring between the Jurassic and Cretaceous periods, roughly 183 to 93 million years ago.

Significant mass extinction events associated with global climate change have also been documented, characterized by rising temperatures, deforestation, wildfires, and oceanic anoxia. The three most notable events include the Late Devonian extinction (380 to 360 million years ago), the Late Carboniferous extinction (around 305 million years ago), and the most severe event of all, the end-Permian mass extinction (approximately 252 million years ago).

In summary, the study of sedimentary layers reveals numerous instances in Earth's geological history where conditions akin to those resulting from human industrial civilization occurred. These include global temperature increases, shifts in carbon isotope ratios, alterations to the nitrogen cycle, oceanic anoxia events, deforestation, mass extinctions, and spikes in metal abundances.

However, none of these geological markers can be definitively linked to an ancient and vanished industrial civilization. It remains impossible to establish through sediment analysis that past climatic changes occurred as rapidly and abruptly as those instigated by human industrial activities. In contrast, events like PETM and ELMO appear to have unfolded over millennia, suggesting that they were driven by natural processes rather than the productive activities of an intelligent species.

Among the potential geological markers of industrial activity, perhaps the most significant arises from carbon utilization for energy. Since the Carboniferous period, roughly 350 to 300 million years ago, sufficient fossil carbon reserves have existed to fuel industrial activities like ours. However, the events that led to the release of large quantities of fossil carbon altering the ¹³C and ¹²C isotope ratios could have entirely natural origins, including volcanic and tectonic activity. Proving the artificial nature of such events is not feasible.

Moreover, it is essential to consider that a truly advanced industrial civilization must minimize its environmental impact to sustain long-term survival. This leads to the paradoxical conclusion that the more evolved an industrial civilization becomes, the fewer geological traces it leaves in sedimentary layers. For instance, if an industrial civilization had existed in the distant past, relying on ecologically sustainable energy sources like geothermal, solar, and wind, it would have produced a far less significant geological impact regarding carbon isotope ratios than our current civilization, which heavily relies on fossil fuels.

In conclusion, both space and time present profound mysteries. It is entirely plausible that multiple industrial civilizations, created by species we may never know, existed during various geological eras. Ultimately, all that remains of such events after millions of years may be a few rare fossils and thin sediment layers composed of minerals whose relative abundances offer only vague and ambiguous insights into the epochs that produced them.