Could humans have brought about on Earth changes so dramatic that they catalysed a whole new geological epoch?
Yes, indeed, suggests a paper in Science , which lists out a range of anthropogenic (human-induced) “signatures” — on land, at sea and in the air — to indicate that the Earth has transitioned from the Holocene to a new epoch: the Anthropocene.
The Anthropocene is a term used informally to describe the age of human-induced change. But the authors say that it may be time for a “formalisation” of the Anthropocene as an entity “equivalent to other formally defined geological epochs.” While opinion is divided on whether or not the Anthropocene is a new geologic time unit, the authors say this era is significantly distinct from the 12,000-year-old Holocene that preceded it.
To back their argument, the scientists enumerate a formidable list of changes that have occurred over the last couple of centuries, from climate change, to heavy metal pollution, deforestation, sea level rise and species extinction.
Concrete, for instance, has become ubiquitous, and the past 20 years (1995–2015) have accounted “for more than half of the 50,000 teragrams of concrete ever produced.” Industrial metals such as cadmium, chromium, copper, mercury, nickel, lead, and zinc have vastly contaminated the earth since the mid-1900s. Fossil fuel combustion produced black carbon that finally peaked at 6.7 teragrams a year in the 1990s.
And if greenhouse gases continue to warm the planet — even at a lower rate than current emissions — then “by 2070, Earth will be … hotter than it has been for most, if not all, of the time since modern humans emerged as a species 200,000 years ago.” Atmospheric CO concentrations have increased by 120-ppm since the mid 1800s. Linked to global warming, the average global sea levels “are currently higher than at any point within the past 115,000 years.”
The paper refers to extensive deforestation in Amazonia, Indonesia, and other parts of Asia and Africa: if the current rate of habitat loss continues, it could “push Earth into the sixth mass extinction event (with 75 per cent of species extinct) in the next few centuries, a process that is probably already underway.”
Nuclear weapons angle So when precisely did the Anthropocene begin? While that’s a question hotly debated, the paper refers to an “inflection point” around 1950 during “the Great Acceleration”, the period of exponential economic growth and resource consumption.
However, “the most widespread and globally synchronous anthropogenic signal” comes from nuclear weapons testing, says the paper, indicating that the Anthropocene may have begun with the detonation of the Trinity atomic device at Alamogordo, New Mexico on July 16, 1945. A paper in the journal Quaternary International last year, similarly suggested that the atomic bomb catalysed the Anthropocene. The Alamogordo, Hiroshima and Nagasaki explosions and other bombs “detonated at the average rate of one every 9.6 days until 1988” released radionuclides across the globe, it said.
It is important to recognise the Anthropocene as a formal geological epoch as it sends out the statement “that we have fundamentally changed our planet to the point it will preserve sediments for millions of years to come that record a world that is now fundamentally different to the one that preceded it,” lead author and principal geologist, British Geological Survey, Colin Waters told The Hindu .
On Anthropocene sceptics, Dr. Waters says: “The Anthropocene is in many ways different to traditional geological units and so is harder to define using traditional techniques. Many would argue that it is too short a timescale and there is need to wait and make judgment once the planet has gone through this pulse of rapid change and has stabilised into a new state.”
divya.gandhi@thehindu.co.in
