Geologists debate if the earth has entered a new geologic time – the Anthropocene epoch. Earth’s history divides itself into eons, eras, periods and epochs. They define significant geologic or paleontological events, such as the emergence of mammals or the mass extinction of the dinosaurs. The conventional geologic theory states we are currently in the Holocene epoch, a segment of time that started at the end of the last ice age, approximately 11,700 years ago.
The Anthropocene—A New Geologic Epoch?
Nobel-prize winning chemist Paul Crutzen and ecologist Eugene Stoermer coined the term “Anthropocene” decades ago. It combines the root “anthropo,” meaning human, with “cene,” the standard suffix for a geologic epoch. During a scientific conference held in 2000, Crutzen argued human activity has so irrevocably altered the face of the earth we have entered a new geologic age. He expanded upon the theory in an article that appeared in the journal Nature in 2002. The term soon began appearing regularly in scientific literature. It is now adopted by the media, although it is not yet formally recognized as an official geologic time.
Cretaceous-Paleogene
Traditionally, geologic “signatures” transition from one geologic time to another. They provide evidence of crucial turning points in earth’s history. In fact, one of the most famous is the Cretaceous-Paleogene or K-Pg boundary (formerly known as the K-T boundary). It marks layers of sediment found throughout the world containing high concentrations of iridium. Although not a rare earth element, it is rather sparse on the planet yet found abundant in asteroids and comets. The discovery of this layer in 1980 gives rise to the theory of the impact of an asteroid on the demise of the dinosaurs and other species. This boundary layer marks the end of the Mesozoic era and the beginning of the Cenozoic era.
Formal Recognition
Many geologists argue that for the Anthropocene recognition as a new geologic epoch, it must demonstrate that the changes are sufficient to leave a signature preserved in geologic strata. This is the position taken by the International Commission on Stratigraphy. Together with its parent organization, the International Union of Geologic Sciences (IUGS), they determine whether the Anthropocene is formally recognized. The entire process of evaluating whether or not to add the Anthropocene to the Geologic Time Scale is expected to take several years.
In the meantime, locating and identifying the elusive boundary layer solidifying the Anthropocene’s place in the geologic timeline has become the Holy Grail of Anthropocene proponents. Finding this evidence would also answer the question—when did the Anthropocene begin. It is a question generating nearly as much controversy as the concept of the Anthropocene itself. According to Dr. Jan Zalasiewicz of the University of Leicester in England, there are three main hypotheses about when the Anthropocene began:
- Some geologists believe it started approximately 8,000 years ago with the advent of agriculture and the resultant deforestation and changes in pollen patterns.
- Others contend truly significant effects did not occur until about 1800 when the human population reached one billion. At about this time, carbon dioxide levels in the atmosphere started to significantly rise due to the burning of fossil fuels during the Industrial Revolution.
- The third theory holds that radioactive fallout from the Nuclear Age that dawned in 1945 marked the start of the Anthropocene.
Still, many geologists do not believe the crucial layer is findable. They argue human activities vary too greatly throughout the world to simultaneously create a sedimentary layer distinguishable enough for future millennia.
Overwhelming Evidence of the Anthropocene
Deforestation in the Amazon
Even without the final geologic signature, proponents of the Anthropocene designation say there is overwhelming evidence in the environment today. Undoubtedly, humans have reshaped the planet on a profound and epic scale. They cite the following:
- Humans affect over three-quarters of the earth’s ice-free land. Currently, people cultivate 38 percent. Reduction of wilderness areas is now approximately 23 percent. Only 11 percent of photosynthesis now occurs in wilderness areas.
- Humans extensively modify the world’s river systems through the construction of dams, levees, canals, and other features. More than half of earth’s rivers have dams. These activities, combined with erosion associated with mining, deforestation, and land development, affect sediment transport patterns worldwide.
- Carbon dioxide from the burning of fossil fuels acidifies oceans. Scientists predict a lasting impact upon rock formation on the sea floor. If the current trend of ocean acidification continues, corals may lose their ability to construct reefs. Thus, it would register in the geologic record as a “reef gap,” a phenomenon characterized in each of the past five major mass extinctions in earth’s history.
- Since the end of WWII, the human population has nearly doubled to almost seven billion; the human biomass calculates as one hundred times larger than that of any other existing large animal species.
Changes in ocean pH levels
- Today, approximately one species is lost every 20 minutes. This rate of extinction is estimated to be 100 to 1,000 times faster than anything found in the fossil record. If destruction continues at this speed, one-fifth of all species currently found on earth will have vanished by 2030.
- Many climatologists believe climate change caused by human activities to fundamentally alter the air, lands, ice sheets, and oceans for tens of thousands of years. Some theorize rising sea levels 20 feet or more. That produces devastating consequences for many life forms.
Are We Living in the Anthropocene?
Has human activity already left an indelible footprint in the geologic record as some geologists believe? Or have we yet to effect enough change to leave our signature? Zalasiewicz, Crutzen, and others described the Anthropocene as representing a new phase in the history of both humankind and of the earth. Is when natural forces and human forces become intertwined so that the fate of one determines the fate of the other. Our continued influence on the earth may indeed determine whether we are in fact living in the Anthropocene.
Note: Earth Systems originally published this article in a newsletter in 2012 and re-edited for the web.
