The Age of Humans

Jordan Healey, Science and Technology Editor, explores the origins of our impact on the planet.

A recent paper written by Simon Lewis and Mark Maslin and published by Nature attempts to identify a starting point for the proposed Anthropocene epoch or the ‘Age of Humans’.  Epochs are subdivisions of the geological timeline that highlight significant changes in geological or atmospheric conditions. The current epoch, the Holocene, began 11,650 years ago following the last Ice Age. Whether or not we are in a new epoch has been contested for many years now, however as it becomes more evident that we are changing the planet. Scientists, such as Nobel Prize winning environmental chemist Paul J. Crutzen, have pushed the idea that industrial activity and farming has been a major driving factor on the planet’s atmosphere and biosphere, to the extent where we are recognised on the geological timeline. This is impressive work on our part when the last 540 million years can be broken down into only 38 epochs, averaging 14.2 million years each! Furthermore, the Anthropocene Working Group was formed in 2008 to determine whether the Anthropocene can be formally defined; this group currently has 38 members, all of whom are responsible in some way for the Geological Time Scale. Lewis and Maslin’s paper, published online on 11 March 2015, attempts to answer the next big question. When did the Anthropocene begin?

The answer is not as obvious as it seems. While many people pinpoint the industrial revolution as the starting point of our influence on the environment, the reality is that the impact of the industrial revolution has been cumulative and no significant point of change can be directly quantified. It is therefore difficult to assign a ‘Golden Spike’ – an internationally agreed upon reference point in a rock unit to identify a new time period. Despite the Industrial Revolution offering no clear ‘Golden Spike’ opportunity, there was a noticeable decline in CO2 found in an Antarctic ice core that dates back to 1610, which predates the industrial revolution by only 150 years. Since this change is preserved in the geological record, it offers a prime opportunity to assign a ‘Golden Spike’. Lewis and Maslin concluded that this would be one of the two most appropriate times to mark the beginning of the Anthropocene.

The second relates to the Great Acceleration, a term used to describe the rapid increase in population and consumption since 1950. Many believe that the finite limits of the planet are dangerously close to being reached, while the population continues to grow along with consumerism, showing no signs of stopping any time soon.This event also coincides with the first nuclear bomb test which occurred on July 16 1945 (the date Crutzen believes marks the start of the Anthropocene). This detonation and subsequent nuclear weapon detonations during World War II and the Cold War will leave their mark on the geology, this can be identified by an abundance of Carbon – 14 and radioactive material in the soils there was an identifiable peak of C-14 concentrations in 1964. While potentially recognisable millions of years from now, this ‘Golden Spike’ is favoured by 2/3 of the current members of the Anthropocene Working Group since it marks the most significant and rapid change in the relationship between humans and nature.

A third theory is known as the ‘Early Anthropocene’ which began around 5000-8000 years ago when wide scale farming and forest clearing began to change the levels of methane and CO2 in the atmosphere. One particular rise in methane levels occurred 5020 years ago and is believed to be due to a rise in farming, particularly of rice. This theory does however lack credibility in relation to the others according to Lewis and Maslin and so they reject it due to a lack of understanding of what exactly caused this change to occur.

The following set of data highlights the changes in CO2 levels in the atmosphere and their relationship with temperature if we assign the start of the Anthropocene to be either 5,020 years ago, in 1610 or in 1964:

Figure 2:


It is clear from these graphs that the climate and CO2 concentrations have been rapidly rising since the mid-twentieth century at a fairly constant rate and so, in my opinion, it would make more sense to mark the beginning of the Anthropocene as either 1945 or 1962. Although the Anthropocene remains a contentious issue amongst scientists of various disciplines, it is clear that we have had an impact on our planet and while some scientists remain optimistic that we can reconcile this impact using technology (much like we overcame overpopulation issues during the Green Revolution).