The 4.54 billion-year history of the earth is divided into many subdivisions: eons, eras, periods, epochs, and ages with each division representing a smaller chunk of geologic time. If you are a parent of a young child and you happen to have viewed several episodes of the children’s educational program Dinosaur Train, you are probably familiar with the Mesozoic Era and the Triassic, Jurassic and Cretaceous periods.
Geologic history is recorded in rocks—layer upon layer accumulates, each layer revealing the geological, ecological and biological events that occurred over the time period that it was deposited. These geologic records tell us about the plants and animal life that could be found hundreds, thousands or millions of years ago. The minerals and chemicals of the rocks can tell us about climate, and sudden changes in the rock layers can tell us about sudden changes on earth.
Many natural forces have shaped the Earth that we know today. Bombardment from extra-planetary objects has left craters and correlate mass extinction events in the geologic record (1). Oceans once covered areas that are now prairies, where if you look long enough or deep enough you might just find a fossil of a previously unknown fish (2). Wind has shaped the earth by eroding and depositing soil. The Loess Hills of western Iowa, USA, (3) and the Loess Plateau of China (4) are two examples of wind-created land forms each created by the slow, wind-driven deposition of soil particles. Of course, water too, is a major force for creating canyons and gorges. The Indus River in Asia, for instance, has been estimated to deepen its course between 2 and 12mm/year in the gorge areas and is capable of removing blocks of rocks measuring up to 70cm (5), and the Grand Canyon in the United States was formed by the erosive power of the Colorado River (6).
So clearly, the forces of Nature on Earth and the occasional meteor from space have played major roles in shaping the Earth that we climb, dive, hike, bike and stroll on today. However, is Nature still the major force at working shaping the Earth? Or is the human species assuming that role?
Geologists describe the epoch in which we live as the Holocene (entirely recent) and characterize it as beginning nearly 12,000 years ago at the end of the last ice age. However, in the 1980s one biologist, Eugene Stoermer from the University of Michigan in Ann Arbor, coined the term “Anthropocene” to describe an epoch in which humans have become the dominant force of change on Earth, and some other scientists are beginning to use that term as well (7,8). But there is debate.
The argument for using a term like Anthropocene is based on observations that human activity has dramatically reshaped the earth. For instance, human-induced soil erosion currently affects 1.6 million km2 (13% of the terrestrial land surface; 10), and mining activities can turn mountains into craters (10), reducing forest cover and leading to flooding and watershed damage. The world human population was estimated at 6.9 billion people in 2010 according to a 2014 World Health Organization report, and if current rates are maintained, the human population is predicted to be 8.3 to 10.9 billion by 2050. With that many individuals occupying the same fixed area, it is easy to see that humans could well be a—if not the—dominant force shaping the Earth.
However, geologic time periods are based on what the rock layers tell us, and geologists who specialize in studying rock layers say that the evidence for a new epoch simply doesn’t exist—yet. These scientists are opposed to co-opting well-defined scientific criteria for establishing geologic time periods to make a point in popular culture (humans are changing things). Instead they ask, “where exactly does the Anthropocene appear in the strata?”
Some proponents of the Anthropocene say that you could start in the 1800s with the Industrial Revolution or even the 1950s with the atomic age, which has left traces of radiation around the globe. Other scientists point out that you can “detect” the signature of agriculture in Europe as early as 900A.D.
I tend to fall in with the geologists who argue that we should maintain our strict criteria for the science of geology. If we change the criteria we use to define and label geologic time periods, then comparisons across history (our own and the Earth’s) become less meaningful. The human species probably won’t know for thousands, or hundreds of thousands of years, when—or if—the Anthropocene began. And, that’s okay. I don’t think we really need a geologic epoch to tell us that the human species is a major force in shaping the Earth and environment that we live in.
- Pope, K.O., D’Hondt, S.L. and Marshall, C.R. (1998) Meteorite impact and the mass extinction of species at the Cretaceous/Tertiary boundary. PNAS USA 95, 11028-29.
- “Incredibly lucky” find yields important fish fossil. PHYS.org http://phys.org/news108387881.html (Internet: Accessed December 1, 2014).
- United States Geologic Survey “Geology of the Loess Hills, Iowa” http://pubs.usgs.gov/info/loess/ (Internet: Accessed December 1, 2014)
- “Dust if you must” The Why Files http://whyfiles.org/shorties/100dust_china/ (Internet: Accessed December 1, 2014)
- Inam, A. et al. (2007) The geographic, geological and oceanographic setting of the Indus River In: Large Rivers: Geomorphology and Management. A. Gupta, ed. John Wiley & Sons, Ltd. https://www.whoi.edu/cms/files/c16_46983.pdf (Internet: Accessed December 1, 2014)
- National Park Service. Grand Canyon National Park Web Site http://www.nps.gov/grca/naturescience/geologicformations.htm (Internet: Accessed December 1, 2014).
- Stevens, A. P. (2014) How people have been shaping the Earth. ScienceNews for Students https://student.societyforscience.org/article/how-people-have-been-shaping-earth (Internet: Accessed December 1, 2104)
- Stromberg, J. (2013) What is the Anthropocene and are we in it? Smithsonian Magazine http://www.smithsonianmag.com/science-nature/what-is-the-anthropocene-and-are-we-in-it-164801414/?no-ist (Internet: Accessed December 1, 2014)
- Bureau of Economic Geology, The University of Texas at Austin. Impact of Soil Conservation Practices on Water Resources in the Loess Plateau, China. http://www.beg.utexas.edu/cswr/loess.html (Internet: Accessed December 1, 2014).
- Lindsey, R. (2007) Coal controversy in Appalachia. NASA Earth Observatory. http://earthobservatory.nasa.gov/Features/MountaintopRemoval/ (Internet: Accessed December 1, 2014).