The Anthropocene: Humankind in the Geological Record

By: Chris Kelly

The Anthropocene?

If the concept of geologic time seems mind-boggling to you, you are not alone.  One of the foremost questions considered by geologists is how to divide the immensity of time on Earth into various chunks, defined by common characteristics.  Generally, these characteristics are based on geological indicators of past environments on Earth: its chemistry, the types of life that existed "way back then," or tectonic changes (think back to your junior high plate diagrams). For example, the Pennsylvanian subperiod roughly 300 million years ago refers to the large amount of coal that was formed in the swamps of ancient Pennsylvania, USA during this time.  Other time periods have been named for intense climatic changes, the extinction of certain species, or the emergence of others.  In 2000, two scientists, Paul Crutzen and Eugene Stoermer, suggested that our current geological time period (the Holocene Epoch) has ended, and we are now living in the "Anthro-pocene."  "Anthro," refers to humankind, while the suffix denotes a division of time associated with very recent time, to geologists at least.  They claim that given the profound human-induced transformation of the planet, we have entered a new geological epoch marked by our own influence. 

Human Impacts, Past and Present:  Scientific and Social Considerations of the Anthropocene

Many modern environmental narratives perpetuate the notion that until the very recent past, humans lived in harmony with the rest of the natural world with minimal environment effects.  This, in short, is a farce.  Modern humans have existed for roughly 200,000 years. Between 50,000 and 10,000 years ago, Australia, North America, and South America all lost between 70 and 90 percent of their largest mammal species.  Although it is possible that past climate change drove these extinctions, scientists increasingly attribute this extinction event to "anthro-pogenic" (human-driven) causes.  Following these extinctions, over the last 11,000 years, mass agriculture developed incrementally, both independently and through cultural cross-pollenation, throughout human societies.  This led to significant conversion of land from forests to farms, and a release of greenhouse gases (which contribute to modern climate change) from the fell trees to the atmosphere.  More recently, after Europeans first made contact with indigenous peoples of present day North and South America, smallpox and other diseases swept across the two continents, killing roughly 50 million people.  That number bears repeating; diseases killed about 90 percent of native peoples in the Americas between 1492 and 1650- six times the number of Jewish and non-Jewish victims that perished in the Holocaust.  Afterward, land that had been cultivated by indigenous peoples reforested, which shows up in geological ice cores as a decline in carbon dioxide.   For those of us living in the United States, the myth of a primeval, unpopulated continent of vast forests is just that- a myth. 

Figure and statistics crafted from Lewis, Simon L., and Mark A. Maslin. "Defining the Anthropocene." Nature 519, no. 7542 (2015): 171-180.  For full facts, statistics, and other examples of preindustrial human impacts, please see the original source.  

Figure and statistics crafted from Lewis, Simon L., and Mark A. Maslin. "Defining the Anthropocene." Nature 519, no. 7542 (2015): 171-180.  For full facts, statistics, and other examples of preindustrial human impacts, please see the original source.  

While these impacts were tremendous, they pale in comparison to modern humanity's capacity to effect environmental change.  Closing the 14th century, there were approximately 380 million people on Earth.  At the time of this blog entry, population is nearly 7.4 billion, an expansion of nearly twenty fold in those last 800 years.   Humans are now the dominant agents of soil erosion, modern extinction, deforestation, and we have changed Earth's atmosphere so profoundly that present levels of greenhouse gases are unprecedented over the last 800,000 years, and likely much longer (3-5 million years).  Human and Earth historians are presently debating how to conceptualize such gargantuan transformations to the earth system:

1) What led to this transformation?

2) How do we define a time period in Earth history dominated by humans in such a whole-sale manner?  Just as geologists term recent Epochs in Earth history the Pliocene, Pleistocene, and Holocene, can we definitively say that there is an "Anthropocene"?

3)  What are the social ramifications of declaring a new time period to mirror this human agency? 


1) To the first question, many narratives of this exponential takeoff in population and environmental impact point to a start date that coincides with either the Industrial Revolution or its subsequent globalization.  The technologies that led to this movement commenced solely in England in 1784 with James Watt's invention of the steam engine, and have spread across the world, if unevenly, ever since.  Indeed, although they were employed by a variety of countries prior to 1950 (mostly Europe, its settler colonial states, and Japan), it is only in the last 65 years that population, plastics, fertilizer consumption, large dams, water use, paper production, and deforestation in the tropics have exploded.  Still, other scientists argue that this most recent "Great Acceleration" is just the longest punctuation in a long history of human environmental impacts- in line with the large mammal extinctions and advent of agriculture of prehistory. 

2) A recent paper in the journal Nature explores the possible start dates, and their respective geological evidence, for an Anthropocene Epoch.  Although it is easy to point to individual historical events, like Watt's steam engine, or archeological evidence for the development of mass agriculture, geologists are searching for slightly different criteria:  distinct, worldwide, synchronous evidence preserved in records the earth itself keeps, such as sediments, ice sheets, tree and coral rings, among others.  Scientists term such a record that preserves clear and discrete evidence of global change a "golden spike."   For example, a layer of the element Iridium  (rare on Earth, but more plentiful on meteorites) in Tunisian rocks was the result of the large impact event that corresponds to the end of the era of dinosaurs (Mesozoic).  More recently, fluctuations in Hydrogen isotopes preserved in Greenland ice sheets herald the Holocene, the recent Epoch in which we presently live. In addition to the golden spikes themselves, the existence of a distinct epoch should be supported by accompanying evidence that suggests global environmental change- like the lack of dinosaur fossils and multiple corroborations of Holocene climate change in sediment, coral, and tree ring records. 

The authors of the aforementioned Nature study suggest two events that have a clear signature in Earth history that could be used to demarcate the geological age of humans.  First, the cataclysmic die-off of indigenous peoples in the Americas is likely preserved in the 1610 carbon dioxide minimum in an Antarctic ice core.  Accompanying evidence could include pollen changes recorded in American lakes, Arctic sea-ice extent, and the coolest temperatures of the associated Little Ice Age.  Second, nuclear weapons testing in the 1950s and 1960s produced measurable levels of radioactive materials; particularly notable is the spike in the radioactive Carbon-14 isotope preserved in ice cores, lake sediments, tree rings, and other Earth recorders.  The authors specifically propose that the 1964 peak in Carbon-14 recorded in a Polish pine tree be the golden spike.  Other evidence could include genetically modified crop pollen, the detection of molecules unique to plastics and refrigerator production in marine sediments, among other hallmarks of the Great Acceleration of population and environmental impact since 1950. 

Ultimately, for the Anthropocene to be officially pronounced, it will take a recommendation by the 'Anthropocene' Working Group, a supermajority when put to vote at the International Commission on Stratigraphy, and ratification at the International Geological Congress.  The earliest opportunity for all this is at the 35th convening in 2016 in Cape Town, South Africa.  Regardless of the outcome, however, the Anthropocene has taken off in the scientific and public consciousness.  

This has tremendous ramifications for us in how we see ourselves and our environmental impact. 

3) Although if viewed impartially it seems as though the actual start date for unprecedented human impact on the earth system seems arbitrary, I would submit that the dialogue tells us just as much about ourselves and our time as does the actual scientific evidence presented.  As this Nature study points out, the difference in describing the present geologic age oftentimes broke down along Cold War lines in the 20th century.  The authors write, "The East-West differences in usage may have been due to differing political ideologies:  an orthodox Marxist view of the inevitability of global collective human agency transforming the world politically and economically requires only a modest conceptual leap to collective human agency as a driver of environmental transformation."  If political affiliations could affect scientific nomenclature then, they certainly could today.  Depending on whether scientists agree on either 1610 or 1964 as the start of the Anthropocene, different stories are privileged.  As the authors describe astutely, 1610 "implies that colonialism, global trade, and coal brought about the Anthropocene," whereas 1964 marks a technological watershed arrived at by a powerful elite of the few wealthiest nation-states on Earth.  As of yet, nuclear weaponry has thankfully not been the most potent factor impacting the environment.  We can only hope this peace endures.

The authors argue that the utmost prudence will be required to make sure that contemporary culture has a minimal effect on scientific definitions of the Anthropocene.  Just this week, a different cohort of scientists argued in a Science Perspectives piece that the formal designation of the Anthropocene is a bad idea partly for this reason, and because it will necessarily fail to recognize the long history of human environmental impact beginning with our global emigration(s) from Africa. 

Whether you find nuances of the debate intriguing or appalling, I leave a plethora of more philosophical points unanswered.  Likely, we in the collective, are leading to the sixth great extinction event in Earth history.  This level of global transformation has occurred before by both living and non-living entities, from the blue green algae that allowed our atmosphere to oxygenate 2.3 billion years ago, to the extraterrestrial object that likely drove the dinosaurs extinct and gave rise to the age of mammals 65 million years ago. But, never before has a sentient species like ourselves caused such wholesale upheaval.  Either addressing, mitigating, or grappling with that kind of power could characterize the psyche of many future generations.

I would be most remiss not to acknowledge that the impetus for this blog entry was provided by a collaborative, forthcoming social history of the Anthropocene by myself and lead authors Nancy Jacobs and Danielle Johnstone at Brown University.  However, I alone accept responsibility for any errors presented in this post.