↑ Pleistocene Holocene/Anthropocene
The Anthropocene is a recent and informal geologic chronological term that serves to mark the evidence and extent of human activities that have had a significant global impact on the Earth's ecosystems. The term was coined by ecologist Eugene Stoermer but has been widely popularized by the Nobel Prize-winning atmospheric chemist Paul Crutzen, who regards the influence of human behavior on the Earth's atmosphere in recent centuries as so significant as to constitute a new geological era for its lithosphere.
In 2008 a proposal was presented to the Stratigraphy Commission of the Geological Society of London to make the Anthropocene a formal unit of geological time. A large majority of that Stratigraphy Commission decided the proposal had merit and should therefore be examined further. Steps are being taken by independent working groups of scientists from various geological societies to determine if the Anthropocene will be formally accepted into the Geological Time Scale.
Many scientists are now using the term and the Geological Society of America titled its 2011 annual meeting: Archean to Anthropocene: The past is the key to the future. The Anthropocene has no precise start date, but based on atmospheric evidence may be considered to start with the Industrial Revolution (late 18th century). Other scientists link it to earlier events, such as the rise of agriculture. Evidence of relative human impact such as the growing human influence on land use, ecosystems, biodiversity and species extinction is controversial, some scientists believe the human impact has significantly changed (or halted) the growth of biodiversity. The Anthropocene may have begun as early as 14,000 to 15,000 years before present, based on lithospheric evidence; this has led other scientists to suggest that "the onset of the Anthropocene should be extended back many thousand years":1; this would be closely synchronous with the current term, Holocene.
The term has Greek roots: anthropo- meaning "human" and -cene meaning "new". Crutzen has explained, "I was at a conference where someone said something about the Holocene. I suddenly thought this was wrong. The world has changed too much. So I said: 'No, we are in the Anthropocene.' I just made up the word on the spur of the moment. Everyone was shocked. But it seems to have stuck." Crutzen first used it in print in a 2000 newsletter of the International Geosphere-Biosphere Programme (IGBP), No.41. In 2008, Zalasiewicz suggested in GSA Today that an anthropocene epoch is now appropriate.
As early as 1873, the Italian geologist Antonio Stoppani acknowledged the increasing power and impact of humanity on the Earth's systems and referred to the 'anthropozoic era'. A similar term, Homogenocene (from old Greek: homo-, same geno-, kind, kainos-, new and -cene, period) was first used by Michael Samways in his editorial article in the Journal of Insect Conservation (1999) titled, "Translocating fauna to foreign lands: here comes the Homogenocene". Samways used the term to define our current geological epoch, in which biodiversity is diminishing and ecosystems around the globe become more similar to one another. The term was used by John L. Curnutt in 2000 in Ecology, in a short list titled "A Guide to the Homogenocene." Curnutt was reviewing Alien species in North America and Hawaii: impacts on natural ecosystems by George Cox. Andrew Revkin coined the term Anthrocene in his book Global Warming: Understanding the Forecast (1992), in which he wrote, "we are entering an age that might someday be referred to as, say, the Anthrocene. After all, it is a geological age of our own making." The word evolved into the Anthropocene, which is generally regarded as being a more suitable technical term.
Definition of epoch
While much of the environmental change occurring on Earth is a direct consequence of the industrial revolution, William Ruddiman has argued that the Anthropocene began approximately 8,000 years ago with the growth of farming. At this point, humans were dispersed across all of the continents (bar Antarctica), and the Neolithic Revolution was ongoing. During this period, humans developed agriculture and animal husbandry to supplement or replace hunter-gatherer subsistence. Such innovations were followed by a wave of extinctions, beginning with large mammals and land birds. This wave was driven by both the direct activity of humans (e.g. hunting) and the indirect consequences of land-use change for agriculture.
This period (10,000 years to present) is usually referred to as the Holocene by geologists. For the majority of the Holocene, human populations were relatively low and their activities considerably muted relative to that of the last few centuries. Nonetheless, many of the processes currently altering the Earth's environment were already occurring during this period.
In terms of trace elements, there are distinct signatures left by modern societies. For example, in the Upper Fremont Glacier, there is a layer of chlorine from 1960s atomic weapon testing programs present in ice cores, as well as a layer of mercury associated with coal plants in the 1980s.
Nature of human effects
Many species have gone extinct due to human impact. Most experts agree that human beings have accelerated the rate of species extinction, though the exact rate is controversial, perhaps 100 to 1000 times the normal background rate of extinction. In 2010 a study published in Nature found that "marine phytoplankton — the vast range of tiny algae species accounting for roughly half of Earth's total photosynthetic biomass - have declined substantially in the world's oceans over the past century. Since 1950 alone, algal biomass decreased by around 40%, probably in response to ocean warming - and the decline has gathered pace in recent years. Some authors have postulated that without human interference the biodiversity of this planet would continue to grow at an exponential rate.
One obvious geological signal of human activity is increasing atmospheric carbon dioxide (CO2) content. During the glacial-interglacial cycles of the past million years, natural processes have varied CO2 by approximately 100 ppm (from 180 ppm to 280 ppm). As of 2011, anthropogenic net emissions of CO2 have increased its atmospheric concentration by a comparable amount from 280 ppm (Holocene or pre-industrial "equilibrium") to about 390 ppm. This signal in the Earth's climate system is especially significant because it is occurring much faster, and to an enormously greater extent, than previous, similar changes. Most of this increase is due to the combustion of fossil fuels such as coal, oil and gas, although smaller fractions are the result of cement production and land-use changes (e.g. deforestation).
Anthropocene temporal limit
Arguing the early Anthropocene hypothesis, William Ruddiman claims that the Anthropocene, as defined by significant human impact on greenhouse gas emissions, began not in the industrial era, but 8,000 years ago, as ancient farmers cleared forests to grow crops. Ruddiman's work has in turn been challenged on the grounds that comparison with an earlier interglaciation ("Stage 11", around 400,000 years ago) suggest that 16,000 more years must elapse before the current Holocene interglaciation comes to an end, and that thus the early anthropogenic hypothesis is invalid. But Ruddiman argues that this results from an invalid alignment of recent insolation maxima with insolation minima from the past, among other irregularities which invalidate the criticism. Furthermore, the argument that "something" is needed to explain the differences in the Holocene is challenged by more recent research showing that all interglacials differ.
However, the fact remains that 8,000 years ago the planet sustained a few million people and was still fundamentally pristine, hence the early Anthropocene hypothesis does not account for a substantial human footprint on Earth.[clarification needed] On the other hand, also the Industrial Revolution proposed by Crutzen  does not seem to be the most suitable start of Anthropocene. In fact, although it is unquestionable that the Industrial Revolution ushered in an unprecedented global human impact on the planet, much of Earth’s landscape had been already profoundly modified by human activities. Anthropocene beginning should hence be anticipated to the moment when humankind has joined with the other environmental forces in shaping the planet. In doing so, it is difficult, perhaps even unrealistic, to identify a Year Zero of the Anthropocene. In fact, the human impact on Earth has grown progressively, with few substantial slowdowns. However, a plausible starting point of the Anthropocene could be at c. 2,000 BP, which roughly coincides with the start of the final phase of Holocene, the Subatlantic.
At this time, the Roman Empire encompassed large portions of Europe, the Middle East and North Africa, in China the classical dynasties were flowering, the Middle kingdoms of India had already the largest economy of the ancient and medieval world, the Napata/Meroitic kingdom extended over the current Sudan and Ethiopia, the Olmecs controlled central Mexico and Guatemala, and the pre-Incan Chavín people managed large areas of northern Peru. Although often apart from each other and intermixed with buffering ecosystems, the areas directly impacted by these civilizations and others were large. Additionally, some activities, such mining, implied much more widespread perturbation of natural conditions.
A marker that accounts for a substantial global impact of humans on the total environment, comparable in scale to those associated with significant perturbations of the geological past, is needed in place of minor changes in atmosphere composition.
A useful candidate for this purpose is the pedosphere, which can retain information of its climatic and geochemical history with features lasting for centuries or millennia. Human activity is now firmly established as the sixth factor of soil formation. It affects pedogenesis either directly, by, for example, land levelling, trenching and embankment building for various purposes, organic matter enrichment from additions of manure or other waste, organic matter impoverishment due to continued cultivation, compaction from overgrazing or, indirectly, by drift of eroded materials or pollutants. Anthropogenic soils are soils markedly affected by human activities, such as repeated ploughing, the addition of fertilizers, contamination, sealing, or enrichment with artefacts (in the World Reference Base for Soil Resources they are classified as Anthrosols and Technosols). They are recalcitrant repositories of artefacts and properties that testify to the dominance of the human impact, and hence appear to be reliable markers for the Anthropocene. Some anthropogenic soils should be hence viewed as the ‘golden spikes’ of geologists (Global Boundary Stratotype Section and Point), which are locations where there are strata successions with clear evidences of a worldwide event, including the appearance of distinctive fossils.
- Anthropogenic biomes
- Effects of global warming
- Holocene extinction
- ^ a b Zalasiewicz, J. et al. (2008). "Are we now living in the Anthropocene". GSA Today 18 (2): 4–8. doi:10.1130/GSAT01802A.1. http://www.see.ed.ac.uk/~shs/Climate%20change/Geo-politics/Anthropocene%202.pdf.
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- ^ 
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- Ruddiman, William F. (2005). Plows, Plagues, and Petroleum: How Humans Took Control of Climate. Princeton, N.J: Princeton University Press. ISBN 0-691-12164-8.
- "The Anthropocene", copy of original IGBP article on Crutzen's website, May 2000.
- "The Anthropocene Debate: Marking Humanity’s Impact", by Elizabeth Kolbert, Yale Environment 360, May 17, 2010
- "Have humans created a new geological age?", NewScientist, January 24, 2008
- Videos of a Radcliffe conference on Biodiversity in the Anthropocene, March 10, 2006
- "Debate over the Early Anthropogenic Hypothesis", RealClimate, December 2005
- "Human-Driven Planet: Time to Make It Official?". Science Now. January 2008. http://sciencenow.sciencemag.org/cgi/content/full/2008/124/1.
- "Earth Is Us", Dot Earth blog, New York Times, January 28, 2008
- "Anthropocene", Encyclopedia of Earth
- Recent work on the Early Anthropocene Hypothesis presented at AGU, December 2008
- (French) Thierry Picquet, "New era in the evolution of the world", Planétarisation
- Humanity Blamed for 9,000 Years of Global Warming
- Nothing new under the sun: Anthropogenic global warming started when people began farming The Economist review; includes nice graphic showing the rise in methane (a greenhouse gas), from agricultural slash-and-burn started 8,000 years ago.
- How Did Humans First Alter Global Climate? Scientific American 2005
- Methane: A Scientific Journey from Obscurity to Climate Super-Stardom NASA
- Anthropocene: Have humans created a new geological age? BBC News, 11 May 2011
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