When and how humans triggered a new geological epoch
There's no doubt that humans have had a powerful impact on the planet, but some scientists believe the effects are so clear and widespread that our current time period should be declared the dawn of a new geological epoch – the Anthropocene. On the path to being formally recognized, a new study has proposed a start date for the new epoch, and outlined where geological evidence could be found to support it.
Conventional thinking has us currently living in the Holocene epoch, which began 11,700 years ago at the end of the last Ice Age. But the world has changed a lot in that time, especially in the last few centuries as human activity has ramped up and started messing with Earth's climate and geology. The situation has gotten to the point where an international team of scientists, calling themselves the Anthropocene Working Group (AWG), has called for a new epoch to be officially declared.
That's no trivial thing. Epochs usually last on the order of many thousands to millions of years, and their transitions are marked in the geological record as observable changes in the chemistry of the rocks, caused by events like volcanic eruptions, asteroid impacts and climate change. Has human activity really left a footprint of that scale?
The AWG argues that our impact on the planet is just as marked as any of the other transitional events. Even if every last human vanished tomorrow, we've already left an imprint that will persist until the Sun swallows the Earth. Future archaeologists will be digging up layers of rock pockmarked with asphalt and concrete, colorful stones fused with hardened plastic, and brand new minerals formed as a result of pollution and human activity.
That sounds like more than enough evidence for the existence of the Anthropocene, but before it can be formally recognized in the Geological Time Scale, a "golden spike" needs to be identified. That's a reference sample of rock layers (or strata) where those key markers are different from earlier layers, clearly showing the transition between two time periods.
While the roots of this new epoch may have been laid as early as the Industrial Revolution, the AWG's work has now identified that the Anthropocene's clearest starting point probably lies around the early 1950s. Physical, chemical and biological markers associated with human activity skyrocket around that time, including the radionuclide fallout left over from nuclear testing and the carbon chemistry changes caused by increased burning of fossil fuels.
A new report from the AWG suggests that these markers should be visible in strata around the world, and the best place to find a golden spike would be on the beds of oxygen-starved seas and lakes, in glacial ice, and preserved in the growth rings of trees and coral.
"This study considers those environments in which the very short history of the Anthropocene is best recorded," says Colin Waters, lead researcher on the study. "In addition to such traditional geological strata, we have also considered human-generated deposits, sediments accumulating in lakes, estuaries and deltas, peat bogs, cave mineral deposits and even biological hosts such as corals and trees. The presence of annual layers or growth rings within many of these provides geologically unprecedented accuracy in the placement of the primary reference marker, wherever this might be ultimately chosen."
The researchers say they are spoiled for choice in terms of finding a golden spike. Once this is collected and studied, the team plans to move forward with a formal proposal to the International Commission on Stratigraphy, which will then vote on whether the Anthropocene is accepted as an official epoch in the history of Earth.
The study was published in the journal Earth-Science Reviews.
Source: University of Leicester