Golden Spike of the Anthropocene

William Ruddiman, a palaeoclimatologist and big name in the Anthropocene debate, identifies the beginning of the Anthropocene as 8000 years ago, in his paper 'The Anthropogenic era began thousands of years ago', 2003. Conversely, Paul Crutzen places the beginning of this new geological epoch much more recently, at the start of the Industrial revolution in the 18th century. At some point in the history of humans, our activity on Earth became significant enough to consider ourselves in a human-caused geological time. So when is this golden spike for the Anthropocene?

The earliest proposed start to the Anthropocene is 50,000 years ago, coinciding with megafauna extinctions, and global human colonisation. The megafauna extinction event saw the loss of many large mammals, as described by the Australian Museum. Robin McKie, science editor for The Guardian, argued in 'What killed off the giant beasts - climate change or man?', 2014, that these extinctions resulted from contributing factors of climate and human activity, at the end of the last ice age. Human hunting of these giant mammals is therefore one of the first anthropogenic impacts on biodiversity on Earth leading to changes in our geology.

Erle Ellis argues that the Anthropocene starts later than this. By 8,000 years ago, with only 'a population of just 10 million or so' the use of agriculture and fire to clear forests had 'altered as much as a fifth of Earth's ice-free land' (Forget Mother Nature: this is a world of our making, 2011). Early farmers without means to plough their land had to move on frequently to more fertile fields, leaving previously cultivated areas in various stages of recovery. This activity created the first 'anthromes' or anthropogenic biomes. By the industrial revolution 'more than half of the terrestrial biosphere had been converted into anthromes', so our impact had already been made on the atmosphere and soil sediments. Today around 38% of terrestrial land is used for farming (Age of man). Similarly, in William Ruddimans' opinion, the early use of agriculture released enough Co2 to prevent another ice age, meaning humans have been the greatest geological force on Earth since the start of the Holocene. Both Ellis and Ruddiman would place the golden spike of the Anthropocene at the dawn of agriculture, potentially replacing the Holocene altogether.

On the other Hand, Paul Crutzen argues in his work The Anthropocene, 2006, that the European industrial revolution marks the significant turning point in human impacts on Earth, 'coinciding with James Watt's design of the steam engine in 1784'. Since the industrial revolution, the burning of fossil fuels and release of Co2 have been represented in ice cores as an 'uninterrupted rise' of carbon dioxide levels. Based on atmospheric composition, the 18th century could mark the greatest change in geology and be seen as the start of the Anthropocene.

The International Union of Geological Sciences will have the final say, who will aim to decide by 2016 whether the Anthropocene will replace the Holocene.