Currently, we are living in the geological epoch of Holocene. The Holocene started 12,000 years ago, at the end of the last Ice Age, and it was characterised by a period of stable climate during which all human civilisation developed. However, since the mid-20th century, the Earth has witnessed a dramatic acceleration of carbon dioxide emissions and of sea level rise, global mass extinction of species, and an extensive land transformation induced by human activities. These human-induced changes could mark the end of that slice of stable climate known as Holocene, and give way to the ‘Anthropocene’.
The ‘Anthropocene’ is a term coined in 2000 by the Nobel Prize-winning chemist Paul Crutzen, together with Eugene F. Stoermer, to denote the present time interval, in which many geologically significant conditions and processes are profoundly altered by human activities. Since then, the term has been widely used (and discussed) by many Earth/ environmental scientists.
Why ‘Anthropocene’? The rationale behind this name is the recognition of the wide-ranging effects that humankind presence and activities are having on the Earth. These human-induced effects include changes in every aspect of the planet, from the atmosphere (air) to the geosphere (soil), passing through the biosphere (living organisms) and to the oceans and waterbodies.
In particular, these human-induced effects include changes in:
- erosion and sediment transportation, which are associated to a variety of anthropogenic processes, including colonisation, agriculture and urbanisation;
- the chemical composition of both atmosphere, oceans and soils. For example, the level of CO2 in the atmosphere has now reached 400 part per million, while it was at 280 ppm just before the industrial revolution. And it is still, currently, rising. In the soils, both nitrogen and phosphorous levels have doubled during the past century due to fertiliser use. This is likely to be the largest impact on the nitrogen cycle in 2.5 billion years. These significant anthropogenic perturbations of the cycles of elements generate associated environmental conditions. Just to quote the most well-known: global warming and ocean acidification.
- the biosphere both on land and in the oceans. Humans have triggered a wave of extinction, threat, and local population declines that is comparable in both rate and magnitude with the five previous mass extinctions of Earth’s history. The effects of this “sixth extinction wave” means that we are likely losing ~11,000 to 58,000 living species every single year (out of estimated total of 5 to 9 million species). And note that this is a conservative count. Across vertebrates, 16 to 33% of all species are estimated to be globally threatened or endangered. Among these, the most threatened are amphibians (41% of all species are globally threatened or endangered), followed by birds (17%), with mammals and reptiles experiencing intermediate threat levels. Loss of invertebrate biodiversity has received much less attention, and data are extremely limited. However, of the species assessed, ~40% are considered threatened. If current trends continue, the Earth is on course to see 75% of species become extinct as a result of habitat loss, predation, species invasions and the physical and chemical changes noted above.
The evidence of the mankind impacts on the planet Earth are truly overwhelming, but these changes are very recent in geological terms. In the Geological Time Scale, an epoch usually spans tens of millions of years, while the ‘Anthropocene’ might have started just around the 1950 (the starting date of the ‘Anthropocene’ is currently widely debated). Furthermore, stratigraphic scientists consider the Geological Time Scale as the very backbone of geology and changes to it are not amended lightly. Today, in fact, the ‘Anthropocene’ is not a formally defined geological unit within the Geological Time Scale. Not yet, at least.
In 2008 an assessment by the Stratigraphy Commission of the Geological Society of London made a case for formally incorporating the term into the Geological Time Scale. Recently, an official expert group called ‘the Anthropocene Working Group” (WGA), which activity started in 2009, has reunited at the prestigious International Geological Congress (held in Cape Town at the end of August 2016) to examine the status, hierarchical level and definition of the ‘Anthropocene’ as a potential new formal division of the Geological Time Scale. Following the discussion, WGA members will spend the next years determining which signals and location show the strongest and sharpest evidence of the start of the Anthropocene, to then make a formal recommendation to declare the ‘Anthropocene’ to the International Commission on Stratigraphy.
Changing the very backbone of geology to include the ‘Anthropocene’ within the Geological Time Scale would be a truly historic decision, which would clearly recognize the responsibility of the human kind in changing the planet Earth atmosphere, geosphere and biosphere.
A number of different starting dates for the ‘Anthropocene’ have been proposed, reflecting different disciplinary approaches and criteria regarding when human societies first began to play a significant role in shaping the Earth’s ecosystems. Two pre-industrial events have occasionally been proposed as markers of the ‘Anthropocene’ beginning; the wave of extinctions of the Pleistocene megafauna and the advent of agriculture (the so-called Neolithic Revolution). Some others proposed the advent of the Industrial Revolution (occurred around 1800) as the a logical start date for the ‘Anthropocene’. Even if it’s probably around this date that human impacts on the Earth’s atmosphere and geosphere became substantial, it’s actually around the 1950 that the human-induced changes have reached what some scientists called the “Great Acceleration”. The “Great Acceleration” has been identified by taking in consideration several different indicators of the development of human enterprise, from the beginning of the Industrial Revolution to the beginning of the new millennium. Such indicators included, between others: human population, damming of rivers, fertilizer consumption, water use, the concentration of atmospheric carbon dioxide and methane, ozone depletion, Northern Hemisphere surface temperature and the loss of global biodiversity. Each and every of these indicators underwent a sharp increase in rate around 1950. For example, the atmospheric carbon dioxide concentration grew from 311ppm in 1950 to 369ppm in 2000. From the perspective of the “Great Acceleration”, the mid-90s appear as good candidate to mark the start of the ‘Anthropocene’.
It has to be considered that a stratigraphic evidence is needed in order to formally define a geological epoch in the Geological Time Scale. In this sense, the WGA suggests the 1945 as the GSSA (Global Standard Stratigraphic Age) for the ‘Anthropocene’. On 16 July 1945, the first nuclear bomb was detonated by the United States Army at Alamogordo, New Mexico. The radioactive elements from nuclear bomb tests blowed into the stratosphere before settling down and being deposited to Earth. However, there would be so many other signals. Other candidates include aluminium and concrete particles, and high levels of nitrogen and phosphate in soils, derived from artificial fertilisers.
Another candidate would be plastic pollution. Humans are putting so much plastic in our waterways and oceans that microplastic particles are now almost virtually ubiquitous, and plastics will likely leave identifiable fossil records for future generations to discover.
About biological signs, the domestic chicken is a serious contender to be a fossil that defines the ‘Anthropocene’ for future geologists. The domestic chicken is a much bigger bird and with a different skeleton than its pre-war ancestor. Since the mid-20th century, it has become the world’s most common bird, being fossilised in thousands of landfill sites and on street corners around the world. The debate around the starting date and the signals that define the beginning of the ‘Anthropocene’ is still ongoing.
On the other hand, some scientists argue that the drive to officially recognize the ‘Anthropocene’ is political rather than scientific. These authors point out that, in contrast to all other units of the Geological Time Scale, the concept of the Anthropocene did not derive from the stratigraphic record. The concept of the ‘Anthropocene’ was formulated first, and stratigraphic evidences are searched as a consequence of this formulation. Furthermore, the ‘Anthropocene’ stratigraphic record is negligible, especially with a boundary set at 1945. Finally, these authors highlight that most of the stratigraphic records mentioned are potential records that might appear in the future.
Others claims that sufficient evidence has emerged of stratigraphically significant changes (both elapsed and imminent) for recognition of the ‘Anthropocene’ . The base of the ‘Anthropocene’ may be defined by a GSSP in sediments or ice core, such as the appearance of manufactured materials in sediments, including aluminium, plastics, and concrete, coinciding with global spikes in fallout radionuclides and particulates from fossil fuel combustion.
So, is the drive to officially recognize the ‘Anthropocene’ political or scientific?
It has to be noted that even in the very first paper in which the term ‘Anthropocene’ was used, the authors themselves declare that he ‘Anthropocene’ epoch initiative as primarily intended to draw attention to the serious ongoing challenge that faces mankind:
“To develop a worldwide accepted strategy leading to sustainability of ecosystems against human induced stresses will be one of the great future tasks of mankind, requiring intensive research efforts and wise application of the knowledge thus acquired in the noösphere, better known as knowledge or information society. An exciting, but also difficult and daunting task lies ahead of the global research and engineering community to guide mankind towards global, sustainable, environmental management” Crutzen & Stoermer, 2000.
Also the reception of the concept of ‘Anthropocene’ had shown a political interpretation:
“Official recognition of the concept would invite cross-disciplinary science. And it would encourage a mindset that will be important not only to fully understand the transformation now occurring but to take action to control it. … Humans may yet ensure that these early years of the Anthropocene are a geological glitch and not just a prelude to a far more severe disruption. But the first step is to recognize, as the term Anthropocene invites us to do, that we are in the driver’s seat. (Nature, 2011, p. 254)”
The debate around the ‘Anthropocene’ formalization is ongoing, scientists are currently researching around this topic to define if the ‘Anthropocene’ can be officially defined as a geological era with scientifically acceptable criteria. A political drive is probably not completely avoidable around this topic, as the concept of the ‘Anthropocene’ has the capacity to become the most politicized unit, by far, of the Geological Time Scales.
While it will be science to tell if we can truly consider the ‘Anthropocene’ as a geological era, the power of this concept shouldn’t be underestimated. The Anthropocene represents a new phase in the history of both humankind and of the Earth, when natural forces and human forces became intertwined so that the fate of one determines the fate of the other.
If even just the debate around this topic can be used to create awareness around these important environmental issues, or as an encouragement to slow carbon emissions and biodiversity loss, or as an evidence in legislation on conservation measures, well, this is a debate that by all means, as humankind, we have the responsibility and the duty to face.
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