Origins of the Anthropocene: Once upon a Timeline

Today, I want to travel back in time.

Let’s begin by creating a timeline of possible GSSPs…

~13,800 years BP: Smith and Zeder posit that Megafaunal predation and vegetation occurred around this time. Whilst this possible GSSP has a secondary marker of charcoal in lacustrine deposits, Maslin and Lewis argue that it a specific start date cannot be ratified from this GSSP as this change came about diachronously over 40,000 years. However, it did have both regional and global reach. Globally, 4% of all mammalian species were lost. Different continents and regions were affected on various magnitudes; Africa lost 18%, Eurasia 36%, N America 72%, S America 83% and an astonishing 88% was lost in Australia.

~11,000 years BP: Initial domestication of plants and animals through farming. Whilst the primary marker has been identified as fossil pollen or phytoliths, and auxiliary markers have also been identified, it is hard to pinpoint a GSSA using this GSSP. The advent of origins of farming is too diachronous.

~8,000 years BP: Alternatively, the arrival of extensive farming could be used as a primary marker. This caused CO2 levels to hit a trough in, however, the CO2 record lacks a distinct inflection at this point of time, and thus a GSSA cannot be determined.

5,020 years BP: Methane levels from wet rice agriculture (Fuller et al., 2011) - finally, a GSSP that has a potential date! The lowest value recorded of CH4 in the GRIP ice core, was 5,020 years BP.  This had regional impacts in Southeast Asia, where it originated from, though consequences were seen globally. However, of course, there is an issue… the auxiliary markers of stone axes and fossil domesticated ruminant remains, only provide weak correlations to changes in Earth System processes, and alas, according to Maslin and Lewis, this cannot be used. *Sigh*. Not to worry, we still have a few more to consider, I’m sure we’ll amble across something viable.

~2,000 years BP: Smith and Zeder suggest the alteration of the Earth’s surface by human civilisations, seen through anthropogenic soils. However, a GSSA cannot be determined from anthropogenic soils and they are not very well preserved, faltering on the 7^th criterion of GSSPs.

1610 AD: Migration of large populations to different continents (Europeans to the Caribbean) led to opening of trade networks and the ‘New-Old world collision’. The GSSP global marker was the atmospheric low of CO2 in 1610, shown in the Law Dome ice core. Possible auxiliary markers range from cross-ocean range extensions of the fossil record to decreases in atmospheric methane and changes in pollen and oxygen. These markers all have strong correlations with changes in Earth System processes. Maslin and Lewis term this irreversible commencement of exchange between continents as the ‘Orbis Spike’. So, finally we have seen the first GSSP, which meets all 7 criteria… Hallelujah!

1760 AD to 1880 AD: The Industrial Revolution! When Crutzen and Stoermer termed this new age the Anthropocene, they linked these new anthropogenic changes to Earth’s climatic systems and processes to the start of the industrial revolution. The population began to expand exponentially, leading to rapid urbanisation and industrialisation through the exploitation of fossil fuels. They argue that extensive use of fossil fuels have lead to shifts in the Earth’s atmospheric composition. The primary stratigraphic marker in this instance would be fly ash from coal burning. However, there are so many markers that could be used, none of which provide clear GSSP global markers.

1945 AD: The detonation of nuclear weapons, in particular of the surface Atomic bombs, caused a global spread of artificial radionuclides. Distinct levels of peak radioactivity were captured by stratigraphical markers ranging from ice cores and tree rings to lake/salt marsh sediments and speleothems (cave formations). The clearest and hence the most viable of these to use, as a primary marker is the peak of ¹⁴C recorded in tree rings and glacial ice. Although captured in Northwest Europe, the effects had global reach and auxiliary markers, such as changes in plutonium isotopes, also indicated defined changes in Earth Systems. Meeting all 7 criteria of GSSPs, this can also be seen as a potential GSSP (Yay)!

1950 AD to present: Due to the Great Acceleration, we have increasingly seen the manifestation of persistent industrial chemicals in ice cores, tree rings and sediments. Peaks have been observed in compounds such as sulphur hexafluoride. Steffen et al., proposes the beginning of the Great Acceleration, as the GSSA of the Anthropocene. Below are the graphs observed by Steffen et al., who conclude there is an irrefutable correlation between mid twentieth century socio-economic trends and functions of the Earth System. However, there are so many effects of the Great Acceleration, it is hard to pick just one to represent the GSSP of the Anthropocene; some even consider the spread of radionuclides as a possible GSSP. It is not possible to use peaks in industrial gases and compounds, as they are all far too recent and there may be peaks soon to come!

 

…And that concludes the timeline (thankfully)! As you will probably have noticed, the two possible GSSPs, fulfilling all 7 criteria, are in turquoise – the Orbis spike and the radioactivity from the A-bombs.

So the big debate is ‘Stage vs. Epoch’. Is the Anthropocene a new stage within the Holocene Epoch or is it the Epoch following the Holocene? Whilst I probably won’t be the defining party on this matter, I personally think the tenable GSSPs we have just come across have shown a tremendous shift in the functionings of our Earth! If the Anthropocene is not worthy of a new epoch, surely there shouldn’t be stratotypes to suggest otherwise? So that’s my philosophy on the subject, what’s yours?

Next post, I will be looking at Steffen et al.’s socio-economic trends graph in greater depth, to finally start understanding what the Anthropocene implies for the economy!