Mark Williams, Francine M.G. McCarthy, Alejandro Cearreta, Martin J. Head, Reinhold Leinfelder, Jens Zinke, Anthony D. Barnosky, Kristine L. DeLong

Extinction, coupled with many other biological signals, is a major geological indicator of the Anthropocene.11Anthony D. Barnosky, Nicholas Matzke, Susumu Tomiya, Guinevere O.U. Wogan, Brian Swartz, Tiago B Quental, Charles Marshall, Jenny L McGuire, Emily Lindsey, Kaitlin Clare Maguire, Benjamin D Mersey, Elizabeth A. Ferrer, “Has the Earth’s Sixth Mass Extinction Already Arrived?,” Nature vol. 471, (2011): pp. 51–57, https://www.researchgate.net/publication/50267709_Has_the_Earth’s_Sixth_Mass_Extinction_Already_Arrived_Nature. The introduction of non-native species, deforestation, depletion of fisheries and modification of coastal environments, domestication of animals, and the reconfiguration of terrestrial ecosystems are all evident in the geological record and are being explored by the Anthropocene Working Group (AWG) and many other investigators. This essay begins by outlining the geological record of life over four billion years, the calamities that have occasionally erased much of its diversity, and the more recent human impacts upon it. We show that lakes, seas, estuaries and wetlands provide important archives of humanity’s reconfiguration of life, and we speculate on the biological and paleontological signature of the near future.

The great interactions of life

The Earth is about 4.5 billion years old, andwithin a billion years of its formation it was alive. For much of geological time life was entirely microbial, but it has grown in mass, organism size, and complexity, in the process transforming the planet to allow more life to diversify. These changes are visible in the geological record.

The early Earth was a very different place. Anoxic chemistry powered the earliest life, as both the atmosphere and oceans lacked breathable oxygen. By 2.5 billion years agocyanobacteria (“blue-green algae”) had harnessed the energy of light to forge biological mass from water and carbon dioxide, releasing oxygen as a “waste” by-product. For much of the early life oxygen was toxic, but other organisms learned to use this “waste” to release more energy through respiration. The ability of life to reuse “waste” is one of its enduring structures, but human ecologies produce so much that Earth is once again in a phase of toxification.

Without oxygen, the metabolic processes of life could not have evolved to allow organisms to get bigger and more complex. The subsequent evolution of animals, over half a billion years ago, and the development of a plant-inhabited landscape from 470 million years ago, restructured life again. All our planet’s systems were impacted by the resulting biochemical changes, eventually producing a world in which bipedal apes characterized by sophisticated cognitive functions could deliberately alter the biosphere (the biosphere is all life and its interactions with air, water and earth). Although geological latecomers—Homo sapiens is just 300,000 years old—humans have developed practices that are highly disruptive to life and may cause a sixth mass extinction.

Five major mass extinctions have occurred over the last 500 million years, resulting from such factors as large-scale changes in the oceans and climate, volcanism, and in one case—the end-Cretaceous extinction 66 million years ago—the impact of a large asteroid in the Gulf of Mexico. Each time at least 75 percent of species diversity was lost, and it took millions of years for the biosphere to recover.

More recent and less catastrophic events may also provide a guide to near future change. The “Great American Interchange” 2.7 million years ago occurred when North and South America became joined at the Isthmus of Panama. Organisms moved both ways between the continents, but physical barriers in the north—a desert to cross in Mexico—and the absence of placental mammals in the south informed the way that ecosystems responded to the exchange. Such insights, even from the remote geological past, can help us understand which of Earth’s ecologies are resilient, and which—like coral reefs and the many species that are nearly extinct—may not be.

Human interaction with the biosphere

For most of human history our impact on the biosphere was negligible. We lived as hunter-gatherers, subsisting off what the land could provide. This lifestyle, now restricted to small groups, is thought able to support a few million people. The first semi-permanent human-made dwellings that were not caves appeared 30,000 years ago. They are part of our increasing technological sophistication that entwines with a record of widespread impacts on large animals during the Late Pleistocene, called the megafauna extinctions.22Paul L. Koch and Anthony D. Barnosky, “Late Quaternary Extinctions: State of the Debate,” Annual Review of Ecology, Evolution, and Systematics, vol. 37 (2006): pp. 215–250.

The first permanent human settlements appeared in the eastern Mediterranean and Near East towards the end of the Pleistocene (from about 13,000 years ago). They are tied to the development of agriculture and pastoralism that accelerated changes to the biosphere — the ArchaeoGLOBE Project has tracked these developments over the past ten millennia.33Lucas Stephens et al., “Archaeological Assessment Reveals Earth’s Early Transformation Through Land Use,” Science, vol. 365 (2019): pp. 897–902, https://science.sciencemag.org/content/365/6456/897.full. Six millennia before the presentmany parts of the world had already witnessed some form of agriculture, though areas of continuous farming were still small. By the time of the Romans, many regions of the Earth showed the imprint of agriculture, and of the exploitation of animals.44David L. Bomgardner, “The Trade in Wild Beasts for Roman Spectacles: A Green Perspective,” Anthropozoologica, vol. 16 (1992): pp. 161–166, https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/az1992n16a20.pdf.

Continued landscape modification has left a paleontological record, for example of the exploitative mechanisms of colonialism. The Columbian Exchange becomes detectable in the fossil record of maize pollen in East African lakes, as does theintroduction of pine trees by European colonizer states during the early twentieth-century “Scramble for Africa.” In eastern North America, European settlement was synonymous with land clearing, where settlers replaced the mixed and deciduous forests with artificial grasslands. This allowed weeds like ragweed (the not-so-aptly named Ambrosia) to proliferate, to the ongoing dismay of allergy sufferers. Contrary to a popular misconception, ragweed was not introduced to North America—it is native to the grasslands in the center of the continent—but the abundance of its pollen grains is a marker of regional land clearing throughout eastern North America. In all, some 95 percent of the Earth’s ice-free landscape is modified in some way by humans;55Christina M. Kennedy, James R. Oakleaf, David M. Theobald, Sharon Baruch-Mordo, and Joseph Kiesecker, “Managing the Middle: A Shift in Conservation Priorities Based on the Global Human Modification Gradient,” Global Change Biology, vol. 25 (2019): pp. 811–826, https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14549. more recently the oceans also show significant evidence of human impact.66Benjamin S. Halpern, Shaun Walbridge, Kimberly A. Selkoe, Carrie V. Kappel, Fiorenza Micheli, Caterina D’Agrosa, John F. Bruno, Kenneth S. Casey, Colin Ebert, Helen E. Fox, Rod Fujita, Dennis Heinemann, Hunter S. Lenihan, Elizabeth M. P. Madin, Matthew T. Perry, Elizabeth R. Selig, Mark Spalding, Robert Steneck, and Reg Watson, “A Global Map of Human Impact on Marine Ecosystems,” Science, vol. 319 (2008): pp. 948–952, https://science.sciencemag.org/content/319/5865/948.full.

Profound signals of biological change are evident in the twentieth century. One catalyst for this change is the chemistry of the Haber-Bosch process, which fixes atmospheric nitrogen to make fertilizers and is now necessary to feed approximately half the world’s human population.77Vaclav Smil, “Detonator of the Population Explosion,” Nature, vol. 400 (1999): p. 415, https://www.nature.com/articles/22672. The scale of this process has left a visible nitrogen signal in the geological record as a marker of the Anthropocene.88Gordon W. Holtgrieve, Daniel E. Schindler, William O. Hobbs, Peter R. Leavitt, Eric J. Ward, Lynda Bunting, Guangjie Chen, Bruce P. Finney, Irene Gregory-Eaves, Sofia Holmgren, Mark J. Lisac, Peter J. Lisi, Koren Nydick, Lauren A. Rogers, Jasmine E. Saros, Daniel T. Selbie, Mark D. Shapley, Patrick B. Walsh, Alexander P. Wolfe, “A Coherent Signature of Anthropogenic Nitrogen Deposition to Remote Watersheds of the Northern Hemisphere,” Science, vol. 334 (2011): pp. 1545–1548. https://pubmed.ncbi.nlm.nih.gov/22174250/. To this profound change we can also add the land appropriated to supply increasing meat consumption, or the use of a wide range of agricultural products such as oil palm that find their way into everything from toothpaste to chocolate, all of which brings about a rapid decrease in living space for nonhumans.

The dramatic increase in the combustion of petroleum in the mid-twentieth century is reflected in the microfossil record, as algae respond to concentrations of atmospheric CO₂ not seen in over three million years. Plants flourish with higher concentrations of the basic raw material of photosynthesis, and they expend less energy taking this in, which is reflected in thedecreased number of breathing pores called stomata in the leaves of land plants.

In the following section we examine how these human impacts play out in many different ecosystems, and how the AWG can use these signals to recognize the Anthropocene.

The fossil record of rapid changes to the biosphere

Humans have caused the extinction of other organisms for millennia, moved animals and plants beyond their native ecologies, and reconfigured ecosystems. Which of these provide a fossil signature for the Anthropocene?

To define a geological boundary, a surface of equivalent time everywhere is needed—an isochronous surface that can be recognized in geological successions globally. Many boundaries in deep time are marked by the first appearance of a particular fossil—such as the mouthparts of a species of marine vertebrates named conodonts in the case of the Triassic System (252 million years ago). This marker, or index fossil, is not present in rocks everywhere, but is sufficiently widespread to enable a chain of correlation with other fossil species of the same age, and with geochemical or other stratigraphical markers. Similar chains of correlation will be needed to identify the Anthropocene.

The first widespread extinction where humans were a causal mechanism is the series of prominent extinctions of large vertebrates termed the “Late Quaternary Extinction” at the end of the last Ice Age. In North America, this coincided with thearrival of the Clovis people replete with sophisticated stone tools for hunting. Large mammals, including the magnificent Irish elk and iconic woolly mammoth, disappeared from Europe and Asia, though the latter survived in the eastern Arctic until about 4,000 years ago. Although these extinctions are widespread, they occurred over tens of thousands of years and do not identify an isochronous surface. Nevertheless, they do identify the regional effects,99Anthony D. Barnosky, Michael Holmes, Renske Kirchholtes, Emily Lindsey, Kaitlin C. Maguire, Ashley W. Poust, M. Allison Stegner, Jun Sunseri, Brian Swartz, Jillian Swift, Natalia A Villavicencio, Guinevere OU. Wogan, “Prelude to the Anthropocene: Two new North American Land Mammal Ages (NALMAS),” The Anthropocene Review, vol. 1, no. 3 (2014): pp. 225–242, https://journals.sagepub.com/doi/full/10.1177/2053019614547433. and progressive global impacts, of the human restructuring of the biosphere.

Human translocation of organisms has occurred for thousands of years, but these have accelerated since the second half of the twentieth century. Some translocations leave little geological trace, but other invasive biological agents do, creating asignal of the almost simultaneous intercontinental dispersal of many marine and terrestrial species in the later twentieth century. Many of these transfers are intimately linked with the local extirpation of native species, and they have had, and will continue to have, the net effect of homogenizing the world’s biota and depleting global biodiversity. Regions that had very different species assemblages prior to human impacts are now looking more and more alike as the same species take over throughout the world.

Species translocations have been facilitated by human communication networks and by extensive habitat modifications that promote the influx of non-native species. Notorious examples include the Zebra mussel— an invader of European rivers for two centuries before migrating to North America in the 1980s, where it rapidly dispersed through the continent’s aquatic ecologies — and the Argentinian Golden Apple Snail, which has rampaged through Southeast Asian rice paddies since the 1980s. Meanwhile, on the west coast of the US, organisms from East Asia invaded the estuary of San Francisco Bay in the 1980s, leaving a fossil signal of their presence.1010Mary McGann, Doris Sloan, and Andrew N. Cohen, “Invasion by a Japanese Marine Microorganism in Western North America,” Hydrobiologia, vol. 421 (2000): pp. 25–30, https://link.springer.com/article/10.1023/A:1003808517945. Identified from historical contexts, human encroachment on estuary ecologies produced dramatic changes, but these have accelerated from the mid-twentieth century.1111Alejandro Cearreta, María Jesús Irabien, Eduardo Leorri, Iñaki Yusta, Almudena Quintanilla, Ane Zabaleta, “Environmental transformation of the Bilbao estuary, N. Spain: Microfaunal and Geochemical Proxies in the Recent Sedimentary Record,” Marine Pollution Bulletin, vol. 44, no. 6 (2002): pp. 487–503, https://doi.org/10.1016/S0025-326X(01)00261-2. Biological signals include the total elimination or reduced biodiversity and abundance of the original biota, the replacement of indigenous species—by others more tolerant of pollution, water acidification and salinity change, and competition with non-native species—and deformities in the skeletons of some organisms, resulting from environmental stress.

Lakes are important continental ecosystems that have been cradles of evolution. Human settlements in their catchments were provided with freshwater, but the lakes received the waste generated by agriculture and industry, and this impairment is recorded by the fossil record of the entire lake ecosystems. The most commonly studied lacustrine microfossils are the glassy remains of diatoms, but many other algae and their consumers—including microscopic invertebrates—preserve in the sediments, allowing entire food webs to be reconstructed. Pollen grains and other remains of terrestrial organisms (including pathogens) that blow or wash into lakes link the surrounding catchment to the lake, allowing cause and effect to be shown between human activities including land clearing and the introduction of exotic species, and the impairment of lake ecosystems. Nutrient loading (eutrophication) has several harmful effects on lakes, including the promotion of harmful algal blooms and the production of anoxic “dead zones.” The associated risks to public health include those posed by harmful algal blooms to the municipal water supply of communities. These have drawn a great deal of attention, but the stresses placed on ecosystems are visible in the turnover in microfossil assemblages in lake sediments long before the impacts are felt directly by humans. For example, lakes in regions with little capacity to buffer against acid rain are stressed by mining and smelting ores and the burning of fossil fuels—especially sulfur-rich coal. Increased acidity mobilizes toxins, making them bioavailable, and this can be seen in deformities in the fossil record of aquatic organisms preserved in the sediments that accumulate in the quiet depths of lake basins. In the best cases, when water does not mix to the lakebed, the past is recorded as annual or even seasonal layers, so that a year-by-year chronicle can be read over thousands of years. These layers of sediment, called varves, can be recovered using freeze cores, hollow metal tubes filled with a slurry of dry ice and ethanol that instantly freezes a rind of lake sediment into which it is pushed, and they can be subsampled and analysed to provide annual resolution for chemical, physical or biological constituents of the lake’s sediment archive.

Some of the most substantial evidence of human impact on life that the AWG is investigating is preserved in the skeletons of corals. Coral reefs have seen massive declines in recent years following coral bleaching events triggered by rapid ocean warming. Significant modifications to coral reef communities in the twentieth and twenty-first centuries have also been caused by damaging cyclones, spikes in predators, and increased sediment delivery to reefs.1212Jens Zinke, James P. Gilmour, Rebecca Fisher, Marji Puotinen, Joseph Maina,Emily Darling, Michael Stat, Zoe T. Richards, Timothy R. McClanahan, Maria Beger, Cordelia Moore, Nicholas A. J. Graham, Ming Feng, Jean-Paul A. Hobbs, Scott N. Evans, Stuart Field, George Shedrawi, Russ C. Babcock, and Shaun K. Wilson “Gradients of Disturbance and Environmental Conditions Shape Coral Community Structure for South-eastern Indian Ocean Reefs,” Diversity & Distributions, vol. 24 (2018): pp. 605–620, https://onlinelibrary.wiley.com/doi/epdf/10.1111/ddi.12714.

Knowing how reef ecologies responded to past environmental change (including past mass extinction events) might provide insights to future patterns.1313Reinhold Leinfelder, “Using the State of Reefs for Anthropocene Stratigraphy: An Ecostratigraphic Approach,” in The Anthropocene as a Geological Time Unit, eds. Jan Zalasiewicz, Colin Waters, Mark Williams, and Colin P. Summerhayes, Cambridge, UK: Cambridge University Press, 2019, pp. 128–136, https://www.researchgate.net/publication/331608833_Using_the_state_of_reefs_for_Anthropocene_stratigraphy_An_ecostratigraphic_approach. Some living reefs thrive in muddy and silty conditions, often in nutrient-rich shallow waters that still resemble the habitats of ancient reefs. With extensive mitigation including preventing overfishing, coastal pollution, and urbanization—and above all, reducing greenhouse gas emissions—coral reefs can continue to grow, albeit in a different form, and possibly thrive well into the future.

Recent coral skeletons also preserve a record of environmental change over hundreds of years, and at a resolution of weeks to months, which makes them the prime archive in tropical oceans. They also record nuclear fallout from weapons testing, pollution, sedimentation, acidification, sea surface saltiness, temperature changes, and changes in skeletal chemistry attributed to the uptake of atoms of carbon derived from the burning of fossil fuels. Corals then offer a high precision tool for establishing when the Anthropocene began.1414Colin Waters, Jan Zalasiewicz, Colin Summerhayes, Ian J. Fairchild, Neil L. Rose, Neil J. Loader, William Shotyk, Alejandro Cearreta, Martin J. Head, James P. M. Syvitski, Mark Williams, Michael Wagreich, Anthony D. Barnosky, An Zhisheng, Reinhold Leinfelder, Catherine Jeandel, Agnieszka Gałuszka, Juliana A.Ivar do Sul, and Matt Edgeworth, “Global Boundary Stratotype and Point (GSSP) for the Anthropocene Series: Where and How to Look for Potential Candidates,” Earth-Science Reviews, vol. 178 (2018): pp. 379–429, https://www.sciencedirect.com/science/article/pii/S0012825217304087.

Because thousands of different species both on the land and in the sea have been translocated across the Earth, and because there are myriad other geological signals by which to build a chain of correlation, the fossil record of the Anthropocene in a coral reef can be linked with records from around the world, including those in colder and deeper waters where coralline algae take over as precise recorders of environmental change. Coralline algae are particularly sensitive proxies of dissolved inorganic carbon (DIC), which is important for understanding atmosphere-ocean interactions. Although there areno instrumental records of DIC prior to the 1970s, acoralline alga from the cold Labrador Sea provides an annually resolved continuous record of DIC variability back to the year 1740 CE. This shows anincreasing influence of anthropogenic carbon dioxide emissions from the 1960s.1515Alicia Meng Xiao Hou, Jochen Halfar, Walter Adey, Ulrich G. Wortmann, Z. Zajacz, Alexandra Tsay, Branwen Williams, Phoebe Chan, “Long-lived Coralline Alga Records Multidecadal Variability in Labrador Sea Carbon Isotopes,” Chemical Geology, vol. 526 (2019): pp. 93–100, https://www.researchgate.net/publication/323313443_Long-lived_coralline_alga_records_multidecadal_variability_in_Labrador_Sea_carbon_isotopes. The specific proxy measured is the relative amount of two isotopes of carbon, ¹²C and ¹³C, denoted as a ratio “δ¹³C” within the skeletal carbonate of the alga. The amount is influenced by anthropogenic emissions of CO₂ that are characterized by isotopically light carbon (¹²C). Some of this isotopically distinctive CO₂ having been discharged into the atmosphere then dissolves into the oceans where it is taken up by the algae (and by corals as well). A multiple site record of δ¹³C from coralline algae in the Arctic Ocean, meanwhile, reflectsvariations in sea-ice cover back to the fourteenth century, with along-term decline since the 1850s probably reflecting industrial-era warming.1616Jochen Halfar, Walter H. Adey, Andreas Kronz, Steffen Hetzinger, Evan Edinger, and William W. Fitzhugh, “Arctic Sea-ice Decline Archived by Multicentury Annual-resolution Record from Crustose Coralline Algal Proxy,” PNAS, vol. 110, no. 49 (2013): pp. 1973736–1973741, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3856805/. In this case, the δ¹³C reflects changes in the primary production of photosynthetic plankton in the waters which are influenced by the annual duration of sea ice cover. Because photosynthetic plankton preferentially use the lighter isotope of carbon, the ambient waters become enriched in the heavier ¹³C that the coralline algae then incorporate into their carbonate skeletons.

Different paths to the future

How might the paleontological signal of the Anthropocene appear to a future geologist? In the near future, as human impacts on the biosphere grow, millions of species may be lost, which would be evident as an abrupt change in the species preserved as fossils in the sedimentary deposits of the Anthropocene. For humans and most of the current biosphere this record will represent a catastrophe. Surviving humans, perhaps the great-grandchildren of today’s children, will live in a world with degraded ecosystems, a world with dramatically diminished land- and seascapes. These patterns are already emerging. Oil palm has exploded across the tropical island of Borneo, whilst the Great Barrier Reef has suffered unprecedented damage in the early twenty-first century.

An alternative fossil record is grounded in a more harmonious relationship with the biosphere. In a world in which we act fast to avert a mass extinction event, the fossil record would still preserve the basal Anthropocene horizon, already evident by the many species we have moved across the world, but this would soon be followed by a paleontological record of recovery, as ecologies repair themselves. This alternative future can become reality: some human cultures are pathfinders for a more sympathetic relationship with the biosphere. They include the indigenous peoples of Haida Gwaii (British Columbia), who use their coastal ecosystems in a sustainable manner.1717Lauren Eckert, Natalie Corinna Ban, Snxakila-Clyde Tallio, and Nancy J. Turner, “Linking Marine Conservation and Indigenous Cultural Revitalization: First Nations Free Themselves from Externally Imposed Social-ecological Traps,” Ecology and Society, vol. 23, no. 4 (2018): p. 23, https://www.researchgate.net/publication/328797343_Linking_marine_conservation_and_Indigenous_cultural_revitalization_First_Nations_free_themselves_from_externally_imposed_social-ecological_traps. They live alongside their aquatic neighbors without exhausting them. At the global level, effective approaches to maintain biodiversity will require trans-national cooperation, a shift to carbon-neutral energy production, and a concerted effort to save many species on the brink. All of these approaches are feasible, if humans have the will.

Mark Williams is a Professor of Palaeobiology at Leicester University. He studies the history of life on Earth over hundreds of millions of years. Most recently he has focused his work on examining the threat to the biosphere from humans.

Francine M.G. McCarthy is Professor of Earth Sciences at Brock University, Canada. Her research focuses on using microfossils to reconstruct paleoenvironmental conditions, primarily on lakes in eastern North America.

Alejandro Cearreta is Professor of Micropaleontology at the Universidad de Pais Vasco UPV/EHU, Spain, Head of the Geology Department and Director of the postgraduate program in Quaternary: Environmental Changes and Human Fingerprint.

Martin J. Head is Professor of Earth Sciences at Brock University, Canada. He studies fossil dinoflagellate cysts to reconstruct oceanographic changes in the geological past, and is currently Vice-Chair of the International Subcommission on Quaternary Stratigraphy.

Reinhold Leinfelder is a Professor of Geobiology at Freie Universität Berlin. He focuses on Earth History, the Past and Future of reefs, and science communication of complex topics. His portfolio also includes museology, future studies, and graphic novels on climate change and the Anthropocene.

Jens Zinke is a Professor in Palaeobiology at the University of Leicester. He focuses on the understanding of natural and anthropogenic impacts from climate change and land use change on tropical coral reefs in the past, present and future across the Indo-Pacific Ocean.

Anthony D. Barnosky is a paleobiologist, global change scientist and professor of biology and executive director of the Jasper Ridge Biological Preserve at Stanford University. His work combines paleontology, biology and conservation biology.

Kristine L. DeLong is Associate Professor in the Department of Geography and Anthropology at Louisiana State University (LSU) in Baton Rouge. Her current research focuses on climate change of the past primarily in the subtropics to tropical regions over the past 130,000 years.

Cover art by Protey Temen, © all rights reserved Protey Temen

Please cite as: Williams, M, F M G McCarthy, A Cearreta, M J Head, R Leinfelder, J Zinke, A D Barnosky, K L DeLong (2022) Biological and Paleontological Signatures of the Anthropocene. In: Rosol C and Rispoli G (eds) Anthropogenic Markers: Stratigraphy and Context, Anthropocene Curriculum. Berlin: Max Planck Institute for the History of Science. DOI: 10.58049/04×5-fw34