39.2: The Anthropocene

Officially, this should be the end of the story. Up to this point, we have explored how the the Quaternary Period, its epochs and ages, have been subdivided using GSSP markers from the past that are clear and can be agreed upon by specialists (more or less). The distinction between GSSPs housed in ice marking boundaries in the Quaternary versus more traditional stratigraphic markers in rock that mark the rest of the time scale does not require a great leap of understanding. But is this the end of the story of our modern geologic time?

Humans are a force of nature. As a single species and in a very short period of geologic time, we have altered the climate, fragmented the rest of the biosphere, and are likely the cause of a sixth mass extinction. Here is a short list of anthropogenic (human-caused) effects on our global environment that, since at least the mid-20th century, are amplified with enough intensity that some have been led to argue that we are in a new geologic moment:

• Humans have been and are altering the composition of our atmosphere. This has been going on since at least 1750 with the onset of the Industrial Revolution in Great Britain, but perhaps as far back as the Neolithic Revolution around 10ka. This includes greenhouse gas emissions such as carbon dioxide (\(\ce{CO2}\)) and methane (\(\ce{CH4}\)), but also chemical and particulate emissions from other industrial, commercial, and household sources. These include black carbon, chlorofluorocarbons (CFCs), HCFCs, etc.;
• Humans are changing the chemical physical composition of the hydrosphere. Again, this has been occurring in increasing intensity since 1750. It includes direct pollution of marine settings chemically and through sewage and litter, as well as indirectly through seawater absorption of excess \(\ce{CO2}\) from the atmosphere (ocean acidification). Surface freshwater and groundwater resources have also been impacted, sometimes catastrophically;
• Humans are changing the layout and composition of the terrestrial and marine biosphere. This alteration includes overhunting of select large game over time, fragmentation of forest and habitat more generally, alteration of landscapes from wild to cultivated for agricultural purposes, and selective elimination of “pests.” It also includes the rapid spread of non-native species to areas due to human commerce. This has led many to hypothesize that we have entered a sixth period of mass extinction, akin to the “big five” (discussed in other chapters);
• Humans are altering the surficial makeup of the geosphere. We are altering coastlines, slopes, and other geomorphology. Our agricultural practices contribute to soil loss, desertification, and the drying up of surface water bodies;
• Humans are altering the exosphere through the addition of space debris;
• Secondary, often amplifying feedback effects, result from all of these. That is, a direct alteration of one environmental variable often leads to a indirect change in another that is not being directly affected by humans. Many times, such effects amplify the negative impacts of the initial human activity through system feedbacks. An example is the human addition of \(\ce{CO2}\) to the atmosphere that leads to warming, which leads to the melting of ice, which leads to lower polar albedo, which leads to more absorption of solar radiation, which leads again to greater warming.

In the history of our planet, it is possible that no single type of organism has ever had this magnitude of an impact (One possible contender is the oxygenation of the atmosphere by cyanobacteria during the Proterozoic). It is definitely the case that the impact of a single species has ever led to change occurring at the rates the planet is now experiencing. For a small taste of this, check out the “Wrecked Wrack” image below. This represents the trash picked up along a 0.8 km (0.5 mile) stretch of the beach on South Padre Island, Texas. These materials could be described variously as anthropogenically-unique materials. You might one day call them technofossils, as they are some of the objects likely to end up as a part of our modern “fossil” record.

These realities are alarming, but also scientifically verifiable. The material pollution documented above is being deposited in sedimentary basins today. It will likely enter the geologic record as a distinct indicator of humanity’s time on the planet.

Because of this, in 2000, atmospheric chemist Paul Crutzen and limnologist Eugene F. Stoermer proposed the creation of a new period of time, the Anthropocene, to mark the age of humans and their effect on the planet. This idea was not entirely new. Soviet scientist Vladimir Vernadsky, in 1938, wrote of human scientific thought itself as a geologic force, using the term Anthropocene for our modern time. The term had also been used by later Soviet scientists as a way to refer to the Quaternary as a whole. Stoermer had been using the term himself since the 1980s, as a way to refer to human impacts on the Earth. The modern use of the term as we will read about it below goes back to a story Paul Crutzen tells of being at a conference where at one point someone mentioned something about the Holocene. Feeling that using this term to describe our current time was wrong, he suddenly stated, “No, we are in the Anthropocene.” By 2008, geologist Jan Zalasiewicz wrote in GSA Today that defining an Anthropocene Epoch is now appropriate. Since then, the ICS has created an “Anthropocene Working Group” which, in 2016, voted to proceed toward identifying a GSSP to define the beginning of an Anthropocene Epoch.

This would mean an end to the Holocene Epoch and Meghalayan Age sometime in our recent past, perhaps within the last 100 years. Indeed, while various start dates have been proposed, some of which will be discussed below, the greatest consensus is forming around a start date of 1950, a date marking a peak in radionuclide fallout from global nuclear testing as well as the start of a time period referred to as “The Great Acceleration.” Since 1950, this acceleration is seen in data wide-ranging enough from the Earth system to cultural and economic trends. Overall, human impacts have led to exponential increases in these trends due to the force of human population growth and increasing development through the use of fossil fuels.

Did I Get It? - Quiz

Exercise \(\PageIndex{1}\)

The human effects on the global environment are well documented. Still, to define a new Age or Epoch, it is necessary to meet certain standards. Which of the following is not a standard for the establishment of a new geologic Epoch?

a. Public opinion

b. A global event that leaves behind a geologic record of itself.

c. A clear stratigraphic marker.

d. A GSSP that can be easily accessed by researchers.

Answer

a. Public opinion

Challenges and Implications

After reading this case study, you may already have identified what may be the greatest philosophical hurdle in defining a new epoch based upon human activity. That is: if our model of geologic time is based upon defining GSSPs using traditional stratigraphic markers (including in ice), how can we define an entirely new geologic age of any kind using markers that may not yet be a part of the geological record? This may seem to go against our model of geologic time and the rules we have used to create it. Does this new designation follow the model and its rules closely enough to be accepted as valid by the scientific community?

A second issue is one of vanity. While certainly the vast majority of the scientific community understands the magnitude of the human impact on the environment, is the definition of a new epoch truly useful in the traditional geologic sense? Or, is it more an exercise in defining our age as a way of encouraging political or social movement toward solving major environmental challenges? How will geologists make use of this epoch – an epoch that may have so far only lasted about 70 years – a blip barely registering in the whole of geologic time? Even if the standard of comparison is the whole Quaternary Period, 70 years is not much.

These are tough academic — even epistemological — questions. The issue is being debated right now among geoscientists. Here, we can only ask the questions rhetorically, but they will beg an answer at some point in the future.

FINDING A START TIME

In a practical sense, the Anthropocene Epoch would need to be defined by a GSSP just like any other boundary on the geologic time scale. This means, succinctly, a geologically-distinct stratigraphic marker that is temporally distinct, clear in the geologic record, easily studied, accessible, and eventually can be ratified by the ICS through agreed upon rules and policies. This has led to lively debate within the ICS’s Subcommission on Quaternary Geology, its Anthropocene Working Group, and among other scholars whose fields of work directly inform the debate. Due to the unique nature of the proposed Anthropocene Epoch and the focus on human impacts, debates over this change have extended beyond just geoscientists. Archaeologists, anthropologists, and specialists in other fields have tossed their ideas and contentions into the fracas. While this has certainly made the identification of a GSSP for an Anthropocene Epoch a whole lot more exciting than the usual act of defining a GSSP, it has also muddied the waters.

The big question is, when do you mark the start of anthropogenic effects? When so much of the Holocene is marked by the story of our species, how do you choose where to draw the line?

The Industrial Revolution: 1750

Because of the clear effects of fossil fuel combustion and their clear, well-documented effect on our changing climate, the start of their widespread usage by humans presents an obvious “go to” time candidate. Data, particularly regarding greenhouse gas \(\ce{CO2}\) emissions since then would seem to support this start date as a clear favorite.

Figure \(\PageIndex{1}\): Carbon dioxide (pink line) has increased along with human emissions (blue line) since 1750. (Source: Climate.gov, adapted from original by Dr. Howard Diamond (NOAA ARL). Atmospheric \(\ce{CO2}\) data from NOAA and ETHZ. \(\ce{CO2}\) emissions data from Our World in Data and the Global Carbon Project.)

Instrumental carbon dioxide records from locations like NOAA’s observatory atop Mauna Loa, Hawaii, have only been collected for a few decades. The graph above is reconstructed from other proxy data, as is the data for human emissions. Still, this would seem to be pretty convincing, particularly if we extend carbon dioxide emissions a bit further back in time.

Figure \(\PageIndex{2}\): Global atmospheric carbon dioxide reconstructions (ppm) for the last 800,000 years to the present from ice core records. Quaternary glacial (valleys) and interglacial (peaks) periods are well recorded here. Throughout the duration of the graph, the highest recorded concentration is 300ppm, at a moment in time over 300,000 years ago, well before there are records of our hominid ancestors’ ability to utilize fire as a tool. (Source: Climate.gov, based on EPICA Dome C data (Lüthi, D., et al., 2008) provided by NOAA NCEI Paleoclimatology Program.)

When examining the chart above, the case for 1750 as a start date for an Anthropocene Epoch seems quite clear.

However, there are a few problems. One of these is that the main data of record is atmospheric carbon dioxide, and that alone. While this is not in itself unusual, identifying a GSSP using the usual rules is challenging. For one thing, it is not necessarily recorded in ice at this point, or reliably, particularly due to the practical issue of global warming having melted so much of the recently deposited ice, and likely to melt a lot more of it in the future. But if the GSSP cannot be identified in ice, it needs to be found in some other solid Earth record that is well-preserved and accessible. While it is possible that an anthropogenic peak in black carbon (such as soot from power plants and factories) could be potentially identified, the sediments that contain it are not yet rock.

There are other problems, but just these few illustrate the challenge of arguing for 1750 as a start date. The start date makes sense culturally and in some limited data, but a GSSP is really hard to identify.

Besides – why start at 1750 when it can be argued that humans have been altering the atmosphere for much, much longer?

The Ruddiman Hypothesis: The Neolithic Revolution at ~10,000 BP

In 2005, William Ruddiman, then a Professor of Environmental Sciences at the University of Virginia, published a book (Plows, Plagues, and Petroleum: How Humans Took Control of the Climate) that argued for a much earlier start date to the Anthropocene. Ruddiman’s idea is known as the “Early Anthropocene” hypothesis, since he argued that human-induced changes in atmospheric greenhouse gases actually began with the advent of agriculture, the Neolithic Revolution.

The idea is very similar to the case for 1750. Human technological innovation has led to major changes in the Earth system. It is just that these effects were from a switch from hunter-gatherer nomadic lifestyles to more sedentary agricultural lifestyles. Agricultural innovations associated with the Neolithic Revolution, such as the domestication of cereal crops beginning around 10,000 BP in the Near East “Fertile Crescent” region containing the Tigris and Euphrates Rivers (modern Iraq, parts of Iran and Turkey, Syria, and Israel/Palestine) and parts of the Mediterranean Sea coast. This particular innovation would develop independently in several other locations, including central China, Egypt, Mesoamerica, central North America along the Mississippi River, and coastal South America. While cereal grain domestication occurred earliest in the Near East, independent development of agriculture in other areas allowed the sharing of technological innovations around the globe.

Prehistoric agriculture, as is still done today, involves the widespread clearing of land and burning of debris. The clearing of land removes vegetation, a natural carbon sink, and its burning then releases carbon back into the system, pumping carbon dioxide into the atmosphere. Some of this carbon had been stored for thousands of years. Such burning for agriculture can still be seen today in places like Indonesia, where massive areas of land are being “slashed and burned” for the planting of palm oil plantations, very often illegally. This burning of debris and accumulated peat is a major source of anthropogenic greenhouse gas emissions today also.

However, widespread burning of debris is not only associated with agriculture. Humans have been using this technique for much longer to burn away underbrush in forests to aid in hunting. When early Europeans arrived in the Americas, for instance, it was observed that it was possible to drive a wagon with four horses side by side with little trouble. Indigenous Americans were able to efficiently clear large swaths of forest in this way. When European disease and warfare drove them out of their lands or killed them altogether, Europeans simply cut down forests or, in the case of forests left standing, did not have a cultural practice of burning underbrush. Thus, it accumulated. Human alteration of the environment over time has turned biomes into anthromes.

Figure \(\PageIndex{3}\): Global centers of origin for agriculture and its spread in prehistory (Source: CCBY-SA 3.0; Joe Roe)

Figure \(\PageIndex{4}\): Anthromes, or Anthropogenic Biomes, dominate the Earth’s landscape (Source: Ellis, 2019). Do we have permission to use this?

Figure \(\PageIndex{5}\): The “Early Anthropocene Hypothesis”. In this hypothesis, it is argued that human land clearance for plant agriculture, including the burning of debris and forest understory, increased carbon dioxide emissions. Shortly after this cultural development, animal husbandry, particularly of ruminants like sheep and cattle, increased methane emissions. These two effects, limited as they were geographically, may have been enough to forestall the natural progression into another glacial period (Source: Ruddiman, 2003). Do we have permission to use this?

Around 8,000 years ago, humans domestication of animals began in earnest. Ruminant animals, in particular, the contributed large amounts of methane to the atmosphere. These animals are still a major source of anthropogenic methane today. Within the rumen of these animals, a group of Archaea known as “methanogens” (Euryarcheota), produce methane from the chewed-up vegetation the animals have eaten. The process is known as enteric fermentation. Contrary to popular imagination, these animals pass this gas into the atmosphere through belching, rather than flatulence. Cumulatively, the amount of methane is very significant.

Both of these gases are potent greenhouse gases. The “Early Anthropocene” argument uses climate modeling to make the case that the collective developments associated with human agriculture were enough to forestall entering a glacial period. Further, this would mean that the climate changes we are experiencing today are simply a more rapid manifestation of climate changes resulting from technological innovations our ancestors made thousands of years ago.

How would this work as a GSSP? This would place the start date for the Anthropocene Epoch at 10,000 BP. With the Holocene Epoch GSSP identified at 11,700 BP, this would either reduce the length of the Holocene to a mere 1,700 years, or make a good argument for either renaming it or just re-imagining how we view the Holocene altogether, thus tossing out the Anthropocene Epoch concept entirely. As for a physical stratigraphic boundary in the rock record, archaeological data could be used to mark a cultural progression, but this would be a significant departure from convention. In reality, we are left with the same problem with using 1750 as a start date. It is nearly impossible to identify a physical location where a rock formation accuratey records this transition.

Is there a time when humans really made their mark in a more explosive manner?

The Atomic Age: 1950 and the “Great Acceleration”

21 days before the first atomic bomb was dropped on the Japanese city of Hiroshima, the first test of an atomic bomb took place near Alamogordo, New Mexico. On July 16th, 1945, the Trinity Test resulted in a 22 kiloton explosion. Below is some of the only footage of that test that exists. The explosion itself can be seen near the end of the clip.

The explosion itself had a yield equivalent to 15,000 to 20,000 tons of TNT. In the years following World War II and until 1963, eight countries developed and tested nuclear weapons. Post-1963, further tests were conducted by Pakistan, India, and North Korea, but these are much more limited in scope. Still, the radionuclide fallout from these early tests, beginning with Trinity, are verifiably recorded in the geologic record.

These nuclear tests represent a technological innovation with power beyond anything else humans have harnessed. Because of this, and because of the global distribution of the radioactive fallout, the emerging consensus is that this period of nuclear testing, beginning in 1945 and extending into the early 1950s, is the ideal temporal horizon to use for the start of the Anthropocene Epoch.

Radionuclide accumulation in the geologic record is not the only significant anthropogenic signal to accumulate from this point. In 2015, scientists with the International Geosphere-Biosphere Programme released their latest data set for what they deem “The Great Acceleration” (Steffen et al., 2004). The idea here is that the rapid and massive growth of socio-cultural trends and Earth system trends beginning around 1950. The advent of the nuclear age and a new source of energy, helped usher in a global industrial revolution that continues its rapid expansion to the present. Socio-economic trends such as human population growth, GDP, fertilizer consumption, urbanization, etc. have put major pressure on the environment. Resulting environmental trends include increases in atmospheric carbon dioxide, nitrous oxides, methane, stratospheric ozone, lower ocean pH (acidification), and forest loss. When graphed, data for all of these groups of variables produce exponential curves, largely beginning around 1950. While not all of these trends will make ideal geologic records, they certainly argue that a rapid increase in anthropogenic population, activity, and energy production has made a lasting impact on the planet.

Figure \(\PageIndex{6}\): Socio-economic and environmental trends included in disucssions of “The Great Acceleration” (Source: IGBP, adapted from Steffen et al., 2004).

The case for an Anthropocene Epoch start date around the year 1950 is compelling. There is a clearly different trend of change in the global natural environment with human activities as the sole or primary driver.

As of this writing, the hunt is still on for a GSSP. It is not unusual to identify a moment in time before a GSSP marker is found, as there are still boundaries on the geologic time scale that completely lack a GSSP to physically define them. Nevertheless, there are a handful of locations being actively pursued as having the potential to contain the key marker for an Anthropocene Epoch. One candidate is Crawford Lake, Ontario, Canada, where its depth precludes complete mixing of layers, allowing its bottom sediments to lie undisturbed. Other sites include an Antarctic ice core, cave deposits in Italy, coral reefs in the Caribbean and Australia, and a peat bog in Switzerland. If present, the signal at all of these locations is a mix of chemical markers consistent with radionuclide fallout, such as carbon-14 and plutonium-239, but also including other potential markers like organic pollutants, microplastics, and fly ash.

RATIFYING A GSSP

The currently agreed-upon temporal marker for the end of the Holocene Epoch and the start of the Anthropocene Epoch is the year 1950. As data documenting the so-called “Great Acceleration” discussed above shows, anthropogenic effects on the environment have increased by orders of magnitude over background rates, been very sudden, progressed very rapidly, and have altered the natural environment enough to be recorded in the geologic record, beginning with radionuclide fallout. The Anthropocene Working Group documents >+1 order of magnitude increases in sediment transport due to urbanization and agriculture; marked and abrupt perturbations in biogeochemical cycling of carbon, nitrogen, phosphorus, and various metals; global warming; global (eustatic) sea-level rise; ocean acidification and proliferation of “dead zones;” rapid biosphere change on land and sea; habitat loss, hyper-predation/hunting, increase of domestic animal populations, and widespread expansion of invasive species; and the abundance and spread of new human-designed substances such as fly ash, plastics, concrete, and technofossils (Anthropogenic Working Group, 2020).

Because these alterations of the Earth system will persist for many millennia (some will be permanent), the Anthropocene Working Group has established that these materials are sufficient to produce durable geologic strata that are sufficiently unique to be separate from Holocene stratigraphy. Because of all of this, the Anthropocene Working Group voted on May 21, 2019 and answered in favor of the following questions at the International Geological Congress in Cape Town, South Africa:

1. Should the Anthropocene be treated as a formal chronostratigraphic unit defined by a GSSP? 29 members voted in favor, 4 voted against.

2. Should the primary guide for the base of the Anthropocene be one of the stratigraphic signals around the mid-twentieth century of the Common Era (i.e., circa 1950)? 29 voted in favor, 4 voted against.

These questions now guide the future work of the ICS’s Anthropocene Working Group. Current work is focused on identifying a GSSP for the Anthropocene Epoch. Candidate locations will certainly be proposed, vetted, and voted upon. The progression from merely suggesting the idea in 2000 to voting on going forward with a formal proposal has only taken 18 years. It is very possible that, within the coming decade, you may find yourself in a new geologic epoch.

Did I Get It? - Quiz

Exercise \(\PageIndex{1}\)

We are living in the Anthropocene Epoch

a. No. A new unit and its GSSP have yet to be ratified.

b. Yes. The new unit has been ratified. A search for the GSSP is ongoing.

Answer

a. No. A new unit and its GSSP have yet to be ratified.