Kurzgesagt – In a Nutshell
Sources – Earth Aliens
We would like to thank the following experts for their support:
Prof. Jason Wright
Department of Astronomy & Astrophysics, The Pennsylvania State University
Dr. Manvir Singh
Postdoctoral Research Fellow, Institute of Advanced Study in Toulouse
Prof. Detlef Gronenborn
Römisch-Germanisches Zentralmuseum, Leibniz-Forschungsinstitut für Archäologie
Sources – Were there other intelligent civilizations in the past?
– When we think about alien civilizations we tend to look into the vastness of space, to far away planets. But there is another incredibly vast dimension that we might be giving too little thought to: time.
We covered the probability of existence of extraterrestrial intelligence in our videos on Fermi Paradox. In case you want to ponder more on the spatial dimension of the vastness, here are the links:
Fermi Paradox I
https://www.youtube.com/watch?v=sNhhvQGsMEc&t=24s
Fermi Paradox II
https://www.youtube.com/watch?v=1fQkVqno-uI&t=30s
– Could it be that over the last hundreds of millions of years, other civilizations existed on earth? Indigenous technological species that rose and died out? And that they or their artifacts are buried beneath our feet? What does science have to say about this and what are the implications for us?
Talking about prior terrestrial industrial civilizations on a scientific foundation can get tricky and fall quickly through the edge of science into the abyss of speculation. Here, we capitalize on the rationale that the lack of evidence would not necessarily rule out the possibility of the existence of those types of civilizations. Therefore, we based our research mainly on the papers evaluating the markers in the geological record that might look like traces of a technological and industrialized civilization – obviously based on our current understanding of industrial requirements (such as heavy usage of energy) – and humans’ current potential to interpret any of those markers as artificial inputs versus natural events. Following two papers, to which we will refer back to multiple times in this source-sheet, explain the reasoning and detail the evidence extensively.
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
– Life on earth has existed for 4 billion years, mostly as single celled organisms until some 540 million years ago the Cambrian explosion heralded the age of animals.
#S. A. Benner, When did Life Likely Emerge on Earth in an RNA-First Process?, 2020
https://arxiv.org/abs/1908.11327
Quote: “We review models for Earth's impact history that invoke a single ~10^23 kg impactor (Moneta) to account for measured amounts of platinum, gold, and other siderophilic ("iron-loving") elements on the Earth and Moon. If it were the last sterilizing impactor, Moneta would have reduced the atmosphere but not its mantle, opening a "window of opportunity" for RNA synthesis, a period when RNA precursors rained from the atmosphere to land holding oxidized minerals that stabilize advanced RNA precursors and RNA. Surprisingly, this combination of physics, geology, and chemistry suggests a time when RNA formation was most probable, ~120 +/- 100 million years after Moneta's impact, or ~4.36 +/- 0.1 billion years ago. Uncertainties in this time are driven by uncertainties in rates of productive atmosphere loss and amounts of sub-aerial land.”
#Britannica, Cambrian Explosion, 2019
https://www.britannica.com/science/Cambrian-explosion
Quote: “Cambrian explosion, the unparalleled emergence of organisms between 541 million and approximately 530 million years ago at the beginning of the Cambrian Period. The event was characterized by the appearance of many of the major phyla (between 20 and 35) that make up modern animal life.”
– A huge time window for our indigenous aliens. Where would we look for them and what could we hope to find? Sadly we have only one civilization to look at: Ourselves.
Here we are working with the assumption that intelligent life would follow from complex life, in other words life which operates on a similar nervous system. Therefore, we exclude scenarios such as great colonies of single celled organisms organizing complex networks and managing a somewhat similar effect to ours. To keep the video in this time frame, we therefore also exclude the probability of a prior explosion of life beyond the reach of the reliable fossil evidence. So if there had been a time before the Cambrian beyond what we could know with the fossil record, with hundreds of thousands of species and they all got destroyed by some apocalyptic event leaving no trace behind at all and life re-started from their cellular remains, no, that is not what we are going to talk about in this one. We adopt this timeframe based on the work:
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
Quote: “The next question is then how long ago could such a species could have existed. Complex life has been common on Earth since the Cambrian ‘explosion’ around 540 Myr ago; before this the fossil record contains only much simpler organisms, such as single-celled species and their colonies. We would then expect that any prior intelligent species to be no older than this event.”
– Anatomically modern humans emerged around 300,000 years ago and probably lived in small groups of hunter gatherers, slowly spreading around the world. Progress was slow and our lifestyle did not change much, although there may have been local bursts of complexity.
Remains of the oldest anatomically modern human so far was found in North Africa a few years ago:
#Hublin et al., New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens, 2017.
https://www.nature.com/articles/nature22336?sf86030179=1
Quote: “Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315 ± 34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent.”
Although the current fossil evidence is rather sporadic and there are many things still awaiting to be dug up, current view indicates that they lived in small groups. Though recent studies suggest that more complex types of living have emerged earlier than thought so far and that period was not that dull after all.There might have been small villages already and various hierarchical organizations. Below are several lines of evidence that are used in support of this argument.
As early as 130,000 years ago, humans were exploiting rich and reliable environmental resources along the coastlines that gave rise to these complex societies:
#Marean C. W. The transition to foraging for dense and predictable resources and its impact on the evolution of modern humans, 2016.
https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.2015.0239
Quote: “The foraging shift to dense and predictable resources is another key milestone that had consequential impacts on the later part of human evolution. The theory of economic defendability predicts that this shift had an important consequence—elevated levels of intergroup territoriality and conflict. In this paper, this theory is integrated with a well-established general theory of hunter –gatherer adaptations and is used to make predictions for the sequence of appearance of several evolved traits of modern humans. The distribution of dense and predictable resources in Africa is reviewed and found to occur only in aquatic contexts (coasts, rivers and lakes). The palaeoanthropological empirical record contains recurrent evidence for a shift to the exploitation of dense and predictable resources by 110 000 years ago, and the first known occurrence is in a marine coastal context in South Africa. Some theory predicts that this elevated conflict would have provided the conditions for selection for the hyperprosocial behaviours unique to modern humans.”
For the interested, the following book provides a more detailed review of the evidence that humans might have not spent most of their evolutionary time as simple tribes of hunter-gatherers and the history of humans could have been fundamentally different than the one told so far.
#David Graeber and David Wengrow, The Dawn of Everything: A New History of Humanity, 2021.
https://us.macmillan.com/books/9780374157357
– Until about 10,000 years ago, when the agricultural revolution changed our lifestyle forever, enabling massive population growth and technological progress.
Here, 10,000 years ago refers to the Neolithic revolution when humans transitioned to a more sedentary lifestyle involving agricultural activities. Having more reliable sources of food through domestication of plants could support a larger population, therefore a rapid increase in birth rates has been detected over a period of several hundred years, though the exact time window varied in different parts of the world. Alongside farming technologies, advancements of making stone tools, clothes and pottery also took place.
#Peter Bellwood and Marc Oxenham, The Expansions of Farming Societies and the Role of the Neolithic Demographic Transition, 2008
https://link.springer.com/chapter/10.1007%2F978-1-4020-8539-0_2
Quote: ”The hypothesis of the Neolithic demographic transition (NDT) postulates that sharp increases in birth rates occurred as populations in different parts of the world adopted sedentary lifestyles and food storage, reduced their birth intervals, and came to depend increasingly on food production as opposed to foraging. For a period after these regional transitions to food production occurred, birth rates and absolute population numbers increased dramatically, at least in those areas (Europe, Middle East, North Africa, North America, Southeast Asia) so far subjected to cemetery analysis. This chapter discusses some general issues connected with early farmer expansion and presents archaeological and cemetery data relevant for an evaluation of the NDT hypothesis from East and Southeast Asia.”
However, it is also worth mentioning that there is recent evidence suggesting humans manipulated their environment even before 10,000 years ago:
#Ellis et al., People have shaped most of terrestrial nature for at least 12,000 years, 2021
https://www.pnas.org/content/118/17/e2023483118.short
Quote: “Even 12,000 y ago, nearly three quarters of Earth’s land was inhabited and therefore shaped by human societies, including more than 95% of temperate and 90% of tropical woodlands. Lands now characterized as “natural,” “intact,” and “wild” generally exhibit long histories of use, as do protected areas and Indigenous lands, and current global patterns of vertebrate species richness and key biodiversity areas are more strongly associated with past patterns of land use than with present ones in regional landscapes now characterized as natural.”
– Rather than just being animals with culture and tools that would have been invisible from space, we became animals that changed the face of the planet, cleared forests and constructed cities and temples for our gods at breathtaking speeds and scales.
Although we tend to concentrate on the post-industrial humans when it comes to leaving a long lasting mark on the planet, pre-industrial humans have left an impact on Earth as well.
#Christopher E. Doughty, Preindustrial Human Impacts on Global and Regional Environment, 2013.
https://www.annualreviews.org/doi/full/10.1146/annurev-environ-032012-095147
Quote: “Humans have had an impact on regional and global environments even prior to the Industrial Revolution through anthropogenic fire, agriculture, and the extinction of the Pleistocene megafauna. The preindustrial impact of anthropogenic fire to modify ecosystems and affect climate may have been small because in regions where impacts were once thought to be large, such as in Australia, the evidence now suggests a smaller effect. Both the extinction of the megafauna, which evidence indicates to be at least partially caused by humans, and preindustrial agriculture may have affected climate, but the effects may have offset each other. For instance, climate simulations indicate that megafauna extinctions may have led to a slight global warming, but later, agriculture led to a slight global cooling. Prior to the industrial era, the largest ecological and climate anomaly may have been associated with forest expansion during the early and mid-Holocene when there were few megafauna and agriculturalists to reduce this expansion.”
The following chart for instance shows the change in the forest land in the last 10,000 years.
#OWID, Deforestation, 2021
https://ourworldindata.org/forest-area
– Until about 300 years ago, we became an industrial species and yet again our numbers grew exponentially as did our impact on the planet.
With the onset of the Industrial Era, the mid-18th century, our lifestyles have drastically changed – alongside our impact on the planet.
#Ellis et al., Anthropogenic transformation of the biomes, 1700 to 2000
Quote: “Between 1700 and 2000, the terrestrial biosphere made the critical transition from mostly wild to mostly anthropogenic, passing the 50% mark early in the 20th century. At present, and ever more in the future, the form and process of terrestrial ecosystems in most biomes will be predominantly anthropogenic, the product of land use and other direct human interactions with ecosystems. Ecological research and conservation efforts in all but a few biomes would benefit from a primary focus on the novel remnant, recovering and managed ecosystems embedded within used lands.”
In the last 300 years, the human population has grown rapidly resulting in probably the most remarkable population change in our history:
#OWID, Population, 2021
Another remarkable increase has been in the greenhouse gas emissions due fossil fuels fulfilling our increased need for energy:
#OWID, Annual CO2 Emissions, 2021
https://ourworldindata.org/grapher/annual-co2-emissions-per-country?tab=chart&country=~OWID_WRL
There are simply so many aspects that fit in here to represent the influence of humans on the environment, from land use change to water use, pollution, climate, use of natural resources, biodiversity decline. In the following paper, authors report one summary statistic, “human footprint”, on global scale compiling data on eight parameters: (1) extent of built environments; (2) crop land; (3) pasture land; (4) human population density; (5) night-time lights; (6) railways; (7) roads; and (8) navigable waterways. Following maps depict how this parameter has changed in the last 16 years. Panel (a) shows the human footprint map for 2009 whereas Panel (b) depicts the absolute change in average human footprint from 1993 to 2009.
#Venter et al. Sixteen years of change in the global terrestrial human footprint and implications for biodiversity conservation, 2016.
– We could say that our 300,000 year long history has three phases: We were hunter gatherers for 97%, farmers for 2.9% and industrialists for 0.1% of our history.
So based on the broad times frames given above in the script, a quick calculation gives us the percentages and shows what a tiny portion of our species history we belong to today. Hunter-gatherers: This covers our 290,000 years until the Neolithic Revolution
Agricultural: The period from Neolithic Revolution to the Industrial Revolution accounts for approx. 2.9% of our time on earth.
Industrialized: The last 300 years makes up only 0.01% of the whole 300,000 years.
– The oldest large scale surface is in the Negev Desert, a meager 1.8 million years old. Everything older has been crushed to dust or turned over and it is either below the ground, or covered by ice or ocean.
#Matmon A. et al. Desert pavement–coated surfaces in extreme deserts present the longest-lived landforms on Earth, 2009.
Quote: “Major factors that reduce erosion converge in these regions: extreme hyperaridity, tectonic stability, flat and horizontal surfaces (i.e., no relief), and effective surface armoring by a clast mosaic of highly resistant lithology. The 10Be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern Negev, Israel (representing the Sahara-Arabia Deserts), indicate simple exposure ages of 1.5–1.8 Ma or correspond to maximum erosion rates of 0.25–0.3 m m.y.−1.”
– Our age, the Anthropocene will be a layer only a few centimeters thick in a few million years.
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
Quote: “We note that effective sedimentation rates in ocean sediment for cores with multi-million-year-old sediment are of the order of a few cm/1000 years at best, and while the degree of bioturbation may smear a short-period signal, the Anthropocene will likely only appear as a section a few cm thick, and appear almost instantaneously in the record.”
– We actually know that in the last few million years, there were hunter gatherers aliens.
Even though only a bunch of Homo species have been discovered so far, it is still a bit overwhelming to keep track of human evolution in the last few million years. All these species of whom we know very little and are somehow alien to us still, were living as hunter-gatherers. The Smithsonian Museum of Natural History has a helpful interactive timeline spanning a few million years, through which one can learn more about different Hominins and the relationship of human evolution with the changes in climate:
#Smithsonian Institution, Human Evolution Interactive Timeline, 2021
https://humanorigins.si.edu/evidence/human-evolution-interactive-timeline
– Our ancestors like Homo Erectus and cousins like the Neanderthals or Denisovans and probably many more that we haven’t found yet or are lost to time forever. They left fragments of their bodies, of weapons and tools and even art.
Today we know that there were other Homo species or subspecies even in the last couple hundred thousand years; Neanderthals, Denisovans, Homo naledi, Homo floresiensis, Homo luzonensis, as well as ghost populations. What we know about them mainly comes from a handful of fossils and analysis of their ancient DNA extracted from those. We have some clues into their lifestyles thanks to the artifacts we found, however there is still much to be found and probably more is lost and never to be found again.
However there are also species that we know from very little evidence. Denisovans for example are known only from a few tiny bone fragments and a few teeth and the actual discovery came through genetics.
#Krause et al.,The complete mitochondrial DNA genome of an unknown hominin from southern Siberia, 2010
https://www.nature.com/articles/nature08976
Quote: “Here we report a complete mitochondrial (mt) DNA sequence retrieved from a bone excavated in 2008 in Denisova Cave in the Altai Mountains in southern Siberia. It represents a hitherto unknown type of hominin mtDNA that shares a common ancestor with anatomically modern human and Neanderthal mtDNAs about 1.0 million years ago. This indicates that it derives from a hominin migration out of Africa distinct from that of the ancestors of Neanderthals and of modern humans. The stratigraphy of the cave where the bone was found suggests that the Denisova hominin lived close in time and space with Neanderthals as well as with modern humans”
The first evidence was a finger bone found in Denisova Cave in Siberia, alongside of which stone tools, animal bones and other artifacts were uncovered as well. Following news article in Nature summarizes the process of discovery and dating of the fossils:
#Robin Dennell, Dating of hominin discoveries at Denisova, 2019
https://www.nature.com/articles/d41586-019-00264-0
Quote: “Previous excavations had uncovered types of ancient ornamental artefact that are often associated with early H. sapiens, such as bones shaped into pendants (Fig. 1) and decorative items made of mammoth ivory. However, the cave hit the news headlines in 2010 when analysis of ancient DNA3 from a bone in a Middle Palaeolithic layer indicated that the
specimen was a previously unknown type of hominin from a branch of the evolutionary tree near H. sapiens. Such hominins were named Denisovans, and, on the basis of DNA
analysis4 , they are probably a sister taxon of Neanderthals.”
There were also the so-called ghost species that we know not directly through fossils but from the DNA fragments found in the fossils of other hominins that could not be assigned to any other known species. Following paper describes one such species:
#Durvasula and Sankararaman. Recovering signals of ghost archaic introgression in African populations. 2020.
https://www.science.org/doi/10.1126/sciadv.aax5097
Quote: “While introgression from Neanderthals and Denisovans has been documented in modern humans outside Africa, the contribution of archaic hominins to the genetic variation of present-day Africans remains poorly understood. We provide complementary lines of evidence for archaic introgression into four West African populations. Our analyses of site frequency spectra indicate that these populations derive 2 to 19% of their genetic ancestry from an archaic population that diverged before the split of Neanderthals and modern humans. Using a method that can identify segments of archaic ancestry without the need for reference archaic genomes, we built genome-wide maps of archaic ancestry in the Yoruba and the Mende populations. Analyses of these maps reveal segments of archaic ancestry at high frequency in these populations that represent potential targets of adaptive introgression. Our results reveal the substantial contribution of archaic ancestry in shaping the gene pool of present-day West African populations.”
We know so little of our ancestors. The fossil evidence is quite scarce and analyzing million year old deposits is a tricky task. A few million years is more than enough time for the sediments to be disturbed by animal burrowing or by subsidence and freeze–thawing cycles. Small bones or stone tools could have easily been displaced from their original positions and been of a different age from the layer of deposits in which they were found.
It does not end with finding a site and excavating a few precious fossils. Dating them is also tricky. Radiocarbon dating for example is usually good for specimens younger than about 50,000 years ago. Other dating techniques like thermoluminescence and optical-stimulated luminescence have been used to date older remains, but they come with their drawbacks, such as wide margins of uncertainty. Despite the difficulties, we are learning more and more with the help of new tools and techniques. Considering how fast new species are discovered in the last two decades and how much our knowledge of them has increased, it is easy to predict that we will learn much more in the near future.
– But what about fossils? We talked about how unlikely the process of fossilization is in more detail in our dinosaur video, but in a nutshell, per hundred thousand years of earth's history we only get a handful of good fossils.
As much as the dinosaur bones and beautifully weird shells of some archaic marine creatures might be commonplace sights in natural history museums, our likelihood of finding and displaying them is in fact quite miniscule. Many things should go right across many different timescales; Animals should have died in the environments that would allow preservation, they should have been of a certain size and part of a certain population depending on their habitat, the cascade of geological events following their death should have worked for us to stumble upon them, the current geopolitics should favor the archeological excavations and so on.
If this has not already made you want to learn more about it, take look at our video:
https://www.youtube.com/watch?v=xaQJbozY_Is
Agricultural and Empire Aliens
– Looking at humans again, agricultural societies left much more to be dug up and found, because they used more sophisticated tools made from sturdier materials and had to feed millions, leaving many more artifacts. Farming allowed them to specialize and develop tech from writing to navigation, architecture and government. Over thousands of years city states became kingdoms and empires, some existing for millennia before they fell.
Early agrarian societies emerged around 3300 BCE in Mesopotamia, Nile River Valley, Indus Valley China and Mesoamerica where fertile river valleys could feed larger populations. These were followed by others in China around 2000 BCE and in today’s Mexico and Central America c. 1500 BCE. There were about 5 million people in the world in 8000 BCE which increased to 14 million by 3000 BCE. As communities grew, different societal structures and leadership styles were adopted. A high-ranking controlling group and a system to force people to pay tribute became the common features of early agrarians. These seem to require a centralized state control which might have motivated formation of cities, states and eventually empires.
Other common traits among these societies were storage of surplus food, development of a state religion, specialized jobs, social rank based on wealth and ancestry, systems of writing, armies and warfare, public architecture (such as temples and pyramids), and increased trade.
#Chapter 6. Agrarian Societies, 2021
http://www.des.ucdavis.edu/faculty/Richerson/BooksOnline/He6-95.pdf
Quote: “The story of agrarian societies continues the themes of the last two Chapters on horticulture and pastoralism. With the continued development of agricultural technology came associated trends in the development of other aspects of culture. Recall that the chief results of plant domestication were (1) greater production per of unit land, (2) higher population densities and sedentary settlements, (3) and increases in material wealth, including stored food and luxury items. Associated with these technical and demographic changes was a substantial increase in the social and political complexity of societies. Large scale military defense and redistribution became more important as wealth increased, the local reliability of subsistence declined, and some specialists removed themselves from personal participation in food production.”
#Agrarian Society
https://www.faculty.rsu.edu/users/f/felwell/www/Ecology/PDFs/Agrarian.pdf
Quote: “The relative wealth of agrarian societies and their settled way of life permit surplus
resources to be invested in new cultural artifacts--paintings and statues, temples, public building and monuments, palaces and stadiums. [...] Writing is also associated with Agrarian society, probably with the need to keep accurate records for the state, trade and taxes. [...] One consequence of the growth of empires was an increase in the economic surplus extracted from conquered peoples in the form of tribute [...] The need for efficient transport and communications in these large societies leads to the development of roads and navies, and previously isolated communities are brought into contact with one another.”
– Many of the buildings or monuments they constructed are still around and traces of them will exist for a few thousand more years. Some only as outlines in the ground, but still recognizable to future archaeologists. The pyramids are piles of limestone so massive that they will probably be around for hundreds of thousands of years.
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
Quote: “The Earth is quite efficient, on cosmic timescales, at destroying evidence of technology on its surface. Biodegredation can destroy organic material in a matter of weeks, and weathering and other forms of erosion will destroy most exposed rock and metals on a timescale of centuries to millennia, if human activity does not erase it faster. At the very longest, some especially large and durable structures in the right environments – the Great Pyramids, for example – might last for tens of thousands of years.”
– Our impact on the planet is orders of magnitude greater than that of our ancestors.
Since we know very little about our ancestors, comparing our impact to theirs is not straightforward. However, we know the magnitudes of our influence and how unlikely it is for them to surpass or even compete with us. A collective account of all environmental parameters would be impossible to put down here. The following article puts together an account of a few relevant parameters:
#The Anthropocene, Max Planck Institute for Chemistry, 2000.
https://www.mpic.de/3865097/the-anthropocene
Quote: “The expansion of mankind, both in numbers and per capita exploitation of Earth's resources has been astounding (5). To give a few examples: During the past 3 centuries human population increased tenfold to 6000 million, accompanied e.g. by a growth in cattle population to 1400 million (6) (about one cow per average size family). Urbanisation has even increased tenfold in the past century. In a few generations mankind is exhausting the fossil fuels that were generated over several hundred million years. The release of S02, globally about 160 Tg/year to the atmosphere by coal and oil burning, is at least two times larger than the sum of all natural emissions, occurring mainly as marine dimethyl-sulfide from the oceans (7); from Vitousek et al. (8) we learn that 30-50% of the land surface has been transformed by human action; more nitrogen is now fixed synthetically and applied as fertilizers in agriculture than fixed naturally in all terrestrial ecosystems; the escape into the atmosphere of NO from fossil fuel and biomass combustion likewise is larger than the natural inputs, giving rise to photochemical ozone ('smog') formation in extensive regions of the world; more than half of all accessible fresh water is used by mankind; human activity has increased the species extinction rate by thousand to ten thousand fold in the tropical rain forests (9) and several climatically important "greenhouse' gases have substantially increased in the atmosphere: CO2 by more than 30% and CH4 by even more than 100%. Furthermore, mankind releases many toxic substances in the environment and even some, the chlorofluorocarbon gases, which are not toxic at all, but which nevertheless have led to the Antarctic 'ozone hole' and which would have destroyed much of the ozone layer if no international regulatory measures to end their production had been taken. Coastal wetlands are also affected by humans, having resulted in the loss of 50% of the world's mangroves. Finally, mechanized human predatim (´fisheries') removes more than 25% of the primary production of the oceans in the upwelling regions and 35% in the temperate continental shelf regions (10). Anthropogenic effects are also well illustrated by the history of biotic communities that leave remains in lake sediments. The effects documented include modification of the geochemical cycle in large freshwater systems and occur in systems remote from primary sources (11-13).”
– The fossil record will show a great extinction of wildlife and an explosion of fossils from human associated animals, like rats, cows, pigs and chickens.
#Plotnicka R. E. & Koy K. A. The Anthropocene fossil record of terrestrial mammals, 2020.
https://www.sciencedirect.com/science/article/abs/pii/S221330541930044X?via%3Dihub
Quote: “We show that a cosmopolitan fauna of humans and their domestic animals will dominate the potential fossil record. The chance of a wild animal becoming part of the fossil record has become very small. Instead, the future mammal record will be mostly cows, pigs, sheep, goats, dogs, cats, etc., and people themselves. The review also shows major unique anthropogenic impacts on the preservation potential of mammals. These impacts include alterations in the distribution and properties of natural sites of preservation, associated with shifts in land use and climate change; the production of novel sites for preservation, such as landfills and cemeteries; and changes in the biostratinomy of animal and human carcasses.”
– Similarly to the structures of our ancestors, skyscrapers and streets and harddrives will basically crumble into nothingness in a few millennia. But because there were so many humans everywhere, for a few million years after our sudden end, there would be clear hints for our existence. The byproducts of our industrialist lifestyle might actually give us away for some hundreds of millions of years.
#Yadvinder Malhi, The Concept of the Anthropocene, 2017.
https://www.annualreviews.org/doi/10.1146/annurev-environ-102016-060854
Quote: “The geological debate has tended to focus on whether there is a detectable stratigraphic signature of the Anthropocene (see the Stratigraphic Support for the Anthropocene section, below), which particular signature is the most appropriate, and how this ends up informing a decision on the start date for the Anthropocene. The aim of the geological approach is to examine the issue of whether contemporary change is detectable and significant on Earth history timescales. A somewhat science fiction thought experiment that is frequently employed is to imagine the mindset of a future geologist (human or alien) millions of years from now, trying to understand the geological record of our time (16). This approach makes defining the Anthropocene as a geological epoch analogous to the process of defining every other past geological period. There is a focus on stratigraphic markers, which tend to be hard bodied, and either marine or lacustrine sediments are particularly favored. There is a preference for dates that are worldwide and exact. A stratigraphic focus also has the advantage of disentangling the debate on definition from some of the political complexities and critiques (see the Critiques from the Social Sciences section, below). It does not seek to either uniformly homogenize or partition humanity in terms of culpability, but rather bases definition on the observed (or potentially observed) geological record (45).”
– We use massive amounts of artificial fertilizer which redirects earth’s flow of nitrogen that is being deposited in the soil.
#OWID, Excess fertilizer use: Which countries cause environmental damage by overapplying fertilizers?, 2021
https://ourworldindata.org/excess-fertilizer
Quote: “This research finds that globally farmers apply around 115 million tonnes of nitrogen to our crops every year. Only around 35% of this is used by them, meaning 75 million tonnes of nitrogen runs off into our rivers, lakes and natural environments. This is our “excess nitrogen”. It is quite staggering that almost two-thirds of our applied nitrogen becomes an environmental pollutant.”
– Mining metals and rare Earth elements leaves long term scars and depletes natural resources.
#Haddaway et al., Evidence of the impacts of metal mining and the effectiveness of mining mitigation measures on social–ecological systems in Arctic and boreal regions: a systematic map protocol, 2019.
https://environmentalevidencejournal.biomedcentral.com/articles/10.1186/s13750-019-0152-8
Quote: “Mining activities, including prospecting, exploration, construction, operation, maintenance, expansion, abandonment, decommissioning and repurposing of a mine can impact social and environmental systems in a range of positive and negative, and direct and indirect ways. Mine exploration, construction, operation, and maintenance may result in land-use change, and may have associated negative impacts on environments, including deforestation, erosion, contamination and alteration of soil profiles, contamination of local streams and wetlands, and an increase in noise level, dust and emissions (e.g. [1,2,3,4,5]). Mine abandonment, decommissioning and repurposing may also result in similar significant environmental impacts, such as soil and water contamination [6,7,8]. Beyond the mines themselves, infrastructure built to support mining activities, such as roads, ports, railway tracks, and power lines, can affect migratory routes of animals and increase habitat fragmentation [9, 10].”
– We saturate our oceans with plastics that find their way to the ocean soil and may persist for hundreds of millions of years.
#Anthony L. Andrady, Persistence of Plastic Litter in the Oceans, 2015.
https://link.springer.com/chapter/10.1007%2F978-3-319-16510-3_3
Quote: “Degradation of plastics occurs primarily through solar UV-radiation induced photo oxidation reactions and is, thus, most intensive in photic environments such as the sea surface and on beaches. The rate of degradation is temperature-dependent resulting in considerable deceleration of the processes in seawater, which is a good heat sink. Below the photic zone in the water column, plastics degrade very slowly resulting in high persistence of plastic litter especially at the seafloor. Biological decomposition of plastics by microorganisms is negligible in the marine environment because the kinetics of biodegradation at sea is particularly slow and oxygen supply for these processes limited.”
#Eriksen M, et al. Plastic Pollution in the World's Oceans: More than 5 Trillion Plastic Pieces Weighing over 250,000 Tons Afloat at Sea, 2014.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0111913
Quote: “Here we report an estimate of the total number of plastic particles and their weight floating in the world's oceans from 24 expeditions (2007–2013) across all five sub-tropical gyres, costal Australia, Bay of Bengal and the Mediterranean Sea conducting surface net tows (N = 680) and visual survey transects of large plastic debris (N = 891). Using an oceanographic model of floating debris dispersal calibrated by our data, and correcting for wind-driven vertical mixing, we estimate a minimum of 5.25 trillion particles weighing 268,940 tons.”
– There are radioactive elements and their decay, unnatural accumulations of elements that do not exist outside labs or weapons.
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
Quote: “Many radioactive isotopes that are related to anthropogenic fission or nuclear arms, have half-lives that are long, but not long enough to be relevant here. However, there are two isotopes that are potentially long-lived enough. Specifically, Plutonium-244 (half-life 80.8 million years) and Curium-247 (half-life 15 million years) would be detectable for a large fraction of the relevant time period if they were deposited in sufficient quantities, say, as a result of a nuclear weapon exchange. There are no known natural sources of 244Pu outside of supernovae.”
– And of course, in our short industrial history we have changed the share of CO2 in the air by burning massive amounts of fossil fuels, increasing the acidity of the oceans and so on.
It is now no question that all that carbon we push into the atmosphere has changed many environmental parameters alongside ocean acidification and we need to change our ways as soon as possible unless we want to aggravate things to an irreversible point for ourselves.
#Le Quéré et al. Global Carbon Budget 2016, 2016
https://essd.copernicus.org/articles/8/605/2016/
Quote: “The concentration of carbon dioxide (CO2) in the atmosphere has increased from approximately 277 parts per million (ppm) in 1750 (Joos and Spahni, 2008), the beginning of the industrial era, to 399.4 ± 0.1 ppm in 2015 (Dlugokencky and Tans, 2016).”
#Orr, J., Fabry, V., Aumont, O. et al. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms, 2005.
https://www.nature.com/articles/nature04095
Quote: “Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation.”
The ways that we have changed the environment would be a very long list assessment of which would not fit in this document. However, two recent reviews summarizes our impact on the biosphere and the consequences of deforestation:
#Folke, C., et al. Our future in the Anthropocene biosphere, 2021.
https://link.springer.com/article/10.1007/s13280-021-01544-8
Quote: “We provide a systemic overview of the current situation where people and nature are dynamically intertwined and embedded in the biosphere, placing shocks and extreme events as part of this dynamic; humanity has become the major force in shaping the future of the Earth system as a whole; and the scale and pace of the human dimension have caused climate change, rapid loss of biodiversity, growing inequalities, and loss of resilience to deal with uncertainty and surprise.”
#Roberts et al., Tropical forests as key sites of the “Anthropocene”: Past and present perspectives, 2021.
https://www.pnas.org/content/118/40/e2109243118
Quote: “The contributions highlight that human societies have not only occupied and utilized these habitats over the long-term, but that they, in many cases, have also actively impacted them. This has often had persistent ramifications for local flora and fauna composition and biology, levels of biodiversity, landscape structure, and regional climate both before and after the industrial era. These deep-time perspectives provide insights for the development of more effective and just management practices in the present and future: ones that take into account the long and shifting cultural histories of these critical environments.”
– We already may have left a mark in the geological record.
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
Quote: “The Anthropocene layer in ocean sediment will be abrupt and multi-variate, consisting of seemingly concurrent-specific peaks in multiple geochemical proxies, biomarkers, elemental composition and mineralogy. It will likely demarcate a clear transition of faunal taxa prior to the event compared with afterwards. Most of the individual markers will not be unique in the context of Earth history as we demonstrate below, but the combination of tracers may be. However, we speculate that some specific tracers that would be unique, specifically persistent synthetic molecules, plastics and (potentially) very long-lived radioactive fallout in the event of nuclear catastrophe. Absent those markers, the uniqueness of the event may well be seen in the multitude of relatively independent fingerprints as opposed to a coherent set of changes associated with a single geophysical cause.”
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
Quote: “Humanity seems to have had a sufficient impact on the Earth that it has created an unambiguous geologic record of its technological activities (the ‘anthropocene’, e.g. Zalasiewicz et al. 2011). A prior species with a similar effect would thus probably have been noticed in the geological record”
– So far we have found no clues for an industrial alien civilization. No layers of weird chemicals or displaced elements. No radioactive layer to indicate that once great nations waged nuclear war. We do see mass extinctions and massive shifts in the fossil records but nove evidence that they did not occur naturally.
Even though the single events of geochemical anomalies or disturbances in fossil record are far from rare, we currently do not have enough evidence to attribute them to anything other than natural events. However, observing the current evidence without ruling out the possibility led to the studies that inspired this video:
#Haqq-Misra J. & Kopparapu R. K. On the likelihood of non-terrestrial artifacts in the Solar System, 2012.
https://www.sciencedirect.com/science/article/abs/pii/S0094576511003122?via%3Dihub
Quote: “The surface of Earth is one of the few places in the Solar System that has been almost completely examined at a spatial resolution of less than 1 m. This is mostly because humans have spread across most of the surface of Earth and would therefore have noticed any NTAs that might exist. (Remaining consistent with the testable zoo hypothesis discussed above, we do not consider NTAs that have been camouflaged so that their detection is nearly impossible.) It may be a stretch to claim that the entire surface of Earth, including land and oceans, has really been searched at a sufficient resolution to discover NTAs; after all, certain caves, jungles, and deserts as well as the complete surface of the ocean may not have been scoured well enough. Additionally, the subsurface of Earth has not been explored anywhere near the resolution to discover such NTAs, if in fact they could reside in the deep ocean or underground. However, nearby objects as small as 1m with Earth-bound trajectories should be detectable by orbital debris tracking systems.”
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
Quote: “Given that it is known to host complex life, the most obvious origin for a prior species of any sort is Earth. Archeology and paleontology, having not found evidence for such a prior species or its technology, put strong constraints on when it might have existed and the longevity of its technosignatures.”
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
Quote: “The specific markers of human industrial activity discussed above (plastics, synthetic pollutants, increased metal concentrations, etc.) are however a consequence of the specific path human society and technology has taken, and the generality of that pathway for other industrial species is totally unknown. Large-scale energy harnessing is potentially a more universal indicator, and given the large energy density in carbon-based fossil fuel, one might postulate that a light δ 13C signal might be a common signal. Conceivably, solar, hydro or geothermal energy sources could have been tapped preferentially, and that would greatly reduce any geological footprint (as it would ours). However, any large release of biogenic carbon whether from methane hydrate pools or volcanic intrusions into organic-rich sediments, will have a similar signal. We therefore have a situation where the known unique markers might not be indicative, while the (perhaps) more expected markers are not sufficient.”
– And ironically we hit upon an interesting problem here: If industrial societies stress the ecosystem enough to cause their own extinction, they won’t be around that long. But if they become sustainable their imprint on the geological record may be tiny. If past industrial civilizations were sustainable before they died out, we may have little to no chance of ever knowing about them.
The sustainability hypothesis was first put forward as a response to one of the propositions of Fermi Paradox that any civilization should have achieved exponential growth to reach galactic-scale. However, it is also suggested that, taking humans as an example, fast growth might not be sustainable on a galactic scale.
#Haqq-Misra and Baum, The Sustainability Solution To The Fermi Paradox, 2009.
https://arxiv.org/pdf/0906.0568.pdf
Quote: “The Fermi Paradox cannot logically conclude that humans are the only intelligent civilization in the galaxy. This is due to the Sustainability Solution to the Fermi Paradox presented here: the absence of ETI observation can be explained by the possibility that exponential growth is not a sustainable development pattern for intelligent civilizations. Thus, the Paradox can only conclude that other intelligent civilizations have not sustained exponential growth patterns throughout the galaxy. It is still possible that slower-growth ETI civilizations exist but have not expanded rapidly enough to be easily detectable by the searches humans have yet made.”
Schmidt and Frank also touch upon a similar idea when they explore the possibility of the prior existence of a terrestrial civilization.
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
Quote: “There is an interesting paradox in considering the Anthropogenic footprint on a geological timescale. The longer human civilization lasts, the larger the signal one would expect in the record. However, the longer a civilization lasts, the more sustainable its practices would need to have become in order to survive. The more sustainable a society (e.g. in energy generation, manufacturing or agriculture) the smaller the footprint on the rest of the planet. But the smaller the footprint, the less of a signal will be embedded in the geological record. Thus, the footprint of civilization might be self-limiting on a relatively short timescale.”
– In any case, over hundreds of millions of years these signatures may become very subtle and get overlooked or interpreted as natural.
Our own techno-signatures have already started resembling previous events in the geological record; events that we attribute to natural phenomena based on the current scientific evidence.
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
Quote: ”The present-day detectability of technosignatures is thus a strong function of their age. Historical records would reveal any such species less than a few thousand years old. Archeology would reveal technosignatures less than a few tens of thousands of years old. The geological record of the past few hundred million years might show a distinct layer if the technology had a widespread geological effect, as ours does. But beyond this, on Gyr timescales the isotopic or chemical signatures of technology on the Earth’s surface might be quite subtle and possibly misinterpreted as natural, or there may be nothing to be found at all.”
– Even if an industrialized alien society existed 200 million years ago and lasted for 100,000 years, 300 times longer than industrial humanity, it still might be easy to miss it in the geological record.
On large time scales like hundreds of millions years, movement of the earth’s crust would topple the traces of any such civilization, rendering open-surfaces inaccessible and covering up all the evidence.
#Wright, J. T. Prior indigenous technological species. International Journal of Astrobiology, 2018.
Quote: “On a timescale of hundreds of Myr or Gyr, however, plate tectonics will subduct almost all evidence for technology with the crust it sits upon, erasing it from the surface entirely. The parts of the surface that escape subduction also change substantially on tectonic timescales, so regions that are easily accessed today might have been practically inaccessible at the time a prior species existed (under miles of ice, for instance) and so show few or no signs of their technology.”
Though, there are several such events in the geological record that might resemble how the Anthropocene would look like in a few hundred millions of years. Based on Wright’ paper above, one such event is The Paleocene–Eocene thermal maximum (PETM). Geochemical analyses on land and in the ocean have pointed to a period 56 million years ago, close to the Paleocene/Eocene border, lasting 100,000 to 200,000 years, featuring a series of interesting events. A few examples from the collection that Wright put together in his paper are as follows:
An abrupt spike in global carbon and oxygen isotopes has been detected:
#Koch et al. Correlation between isotope records in marine and continental carbon reservoirs near the Palaeocene/Eocene boundary, 1992.
https://www.nature.com/articles/358319a0
Quote: “The carbon isotope compositions of marine carbonate sediments from the late Palaeocene vary considerably, exhibiting a sudden decrease close to the Palaeocene/Eocene boundary which coincides with deep-sea benthic extinctions1 and with changes in ocean circulation. Here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel. In using palaeosol carbonates to reconstruct the CO2 content of the ancient atmosphere2, isotope shifts of this sort will have to be taken into account. The sharp decrease in 13C/12C ratios in the late Palaeocene provides a datum for precise correlation of marine and continental records, and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals.”
There was a swift input of exogenous carbon into the atmosphere and to the ocean alongside a temperature increase of 5-7 °C:
#Kirtland Turner et al., A probabilistic assessment of the rapidity of PETM onset, 2017
https://www.nature.com/articles/s41467-017-00292-2
Quote: “During the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), the rapid injection of isotopically depleted carbon to the atmosphere (and/or ocean) was imprinted in the geological record as a prominent negative carbon isotope excursion. Associated with this is evidence for a ~5 °C global temperature rise, ocean acidification, and a variety of global biotic changes in marine and terrestrial archives1,2,3,4. The PETM is thus widely recognized as the best known analog to date for future greenhouse-gas-driven global warming5. However, the timescale of the event is critical to the value of inferences that can be drawn regarding future climate change and ecosystem response6—particularly with respect to the duration of main carbon release (PETM onset), which we define as the interval between pre-PETM carbon isotope values and the recorded carbon isotope minimum.”
Another study analyzed geochemical features of beds from south Egypt dated to Paleocene/Eocene border and spotted an increased amount of trace elements such as zinc, molybdenum, vanadium, chromium:
#Soliman et al., Enhanced coastal paleoproductivity and nutrient supply in Upper Egypt during the Paleocene/Eocene Thermal Maximum (PETM): Mineralogical and geochemical evidence, 2017.
https://www.sciencedirect.com/science/article/abs/pii/S003101821100410X
Quote: “The Dababiya Quarry Member of the Esna Shales provides an ~200 kyr record of lithological, sedimentological, paleontological and geochemical changes associated the PETM (~55.9 Ma) in the southern Tethys (Egypt). This geochemical analysis of the DQM recovered from a core taken in the Dababiya Quarry, ~200 m away of the GSSP of the base of the Eocene, complements earlier studies of correlative sections in Upper Egypt, and provides new evidence for enhanced coastal productivity associated with the PETM. The high enrichment of the DQM in chalcophile elements (U, P, Mo, Zn, Cd, V), organic matter (up to 1.7% TOC) and phosphatic debris constitute evidence for deposition under anoxic conditions.”
All these changes are very much similar to the geochemical signature of Anthropocene:
#Schmidt, G., & Frank, A. The Silurian hypothesis: Would it be possible to detect an industrial civilization in the geological record?, 2019. https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6
Quote: “There are undoubted similarities between previous abrupt events in the geological record and the likely Anthropocene signature in the geological record to come. Negative, abrupt δ 13C excursions, warmings and disruptions of the nitrogen cycle are ubiquitous. More complex changes in biota, sedimentation and mineralogy are also common. Specifically, compared with the hypothesized Anthropocene signature, almost all changes found so far for the PETM are of the same sign and comparable magnitude.”