One big debate in science is whether the impacts of human actions on earth are now so large that we have entered a new geological time. Called the Anthropocene, its formal designation would mean the old forces of nature that transformed our planet many millions of years ago, including meteorites and mega-volcanoes, are joined by another: us. What geologists call the Holocene Epoch would be over. The exact date would be up for debate, but it would probably be within the past few hundred years.
A formal decision on this had been expected. Instead, an announcement by the International Union of Geological Sciences (IUGS) declared that we are still officially in the Holocene but that since 4,200 years ago we have in fact been in a sub-period called the Meghalayan Age. Confused? Well join the club.
Like Russian dolls, geological time is split into ever finer nested units. Eons are the longest, followed by Eras then Periods then Epochs and finally Ages. The IUGS has ratified a proposal to split up the Holocene Epoch into three Ages. First the Greenlandian Age which runs from the start of the Holocene at 11,700 years ago to 8,326 years ago when the Northgrippian starts. This Age runs to 4,250 years ago when the Meghalayan starts, which continues to the present. They more-or-less define the early, middle and late Holocene.
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The Meghalayan Age is defined by a mega-drought that caused the collapse of a number of civilisations, including Mesopotamia, the Indus Valley and the Yangtze River Valley. Most well-known is the collapse of the Old Kingdom in Egypt, a civilization that had prospered for over 450 years building over 20 giant pyramids. The IUGS has referred to this event as a worldwide collapse of civilization, forgetting the tens of millions of people living in civilisation in the Americas, Africa and elsewhere. The name of the Age comes from the northeastern Indian state of Meghalaya where a stalagmite was recovered from a cave that provides chemical evidence of the drought.
Human impact
But where does this leave the Anthropocene debate? Because the evidence for a human dominated geological Epoch is overwhelming. Humans move more soil, rock and sediment each year than is transported by all other natural processes combined. Humans have made enough concrete to cover the whole surface of the Earth in a layer 2 mm thick. They make over 300 million tonnes of plastic per year. Humans have increased atmospheric carbon dioxide levels by over 45 per cent, acidifying the oceans and raising Earth鈥檚 temperature by nearly 1藲C 鈥� delaying the next ice age by tens of thousands of years. And if you weigh all land mammals in the world, 30 per cent is the weight of humans, 67 per cent our livestock with just 3 per cent being wild mammals. These human impacts are now seen in almost all sediments, including ice cores and cave stalagmites.
By ignoring all this evidence and defining the present day as the Meghalayan, it seems like a small group of scientists that are wedded to the Holocene concept have confused the public and may well have made the discussion and ratification of the Anthropocene that much harder.
As we write in our new book The Human Planet, there seems to be a lack of rational debate and discussion about how we define geological time that includes the present day. The choice to formally define the Holocene as the Epoch we live in is strange: it is a normal interglacial, of which there have been many over the past 2.6 million years, until humans really begin changing the environment on a global scale. The announcement to divide it further only highlights the limitations of defining the current interglacial as an Epoch.
Geological dispute
At the level of Ages, having the Meghalayan run to the present day is extremely odd. On a narrow view of just climate change, in recent decades our greenhouse gas emission mean air temperatures exceed those of the Holocene that are recorded in ice-core records, but are ignored in this new division of the Holocene.
A sensible way forward would have looked at all the data together to get some agreement across many scientific fields.聽 Instead we have a situation where the group of scientists tasked with looking at dividing the Holocene did not coordinate with the group of scientists tasked to consider the Anthropocene. The group that handed in its proposal first to the IUGS to change the formal Geologic Time Scale got their way, with nearly everyone left confused.
Little related to the division of geological time has widespread public relevance. But the debate about the time we live in does. Geologists should take a step back from their disputes and think about what is in the wider interests of science and the public understanding of it. Announcing a new Meghalayan Age while not placing this in the context of the evidence for the Anthropocene does a disservice to those who wish to understand what impact human actions are having on the planet in a geological context.
Mark Maslin is Professor of Earth System Science University College London.
Simon Lewis is Professor of Global Change Science at University College London and the University of Leeds. They are authors of (Penguin)
