It’s official. More than 8,000 years ago, a vast amount of water from melting glaciers flooded North America and caused havoc with the currents and atmosphere of the North Atlantic.
That significant event, during the Middle Holocene Northgrippian Age, was followed by droughts and cold temperatures in various parts of the globe that wiped out several civilizations during the Late Holocene Meghalayan Age more than 4,000 years ago.
Scientists have long known about this history. What’s now official are the geological time periods in which these events occurred.
Late last month, the International Union of Geological Sciences officially approved three ages of the Holocene epoch: Early Holocene Greenlandian Age; Middle Holocene Northgrippian Age; and Late Holocene Meghalayan Age.
Laying the groundwork for this sub-division was the International Subcommission on Quaternary Stratigraphy — Quaternary referring to the period under which the Holocene epoch falls.
Brock University Professor of Earth Sciences Martin Head chairs the subcommission, made up of geologists around the globe. He is also co-author of the academic article that reports these changes to the time scale along with lead author Professor Mike Walker of the University of Wales.
Head says his group debated a proposal by international Earth experts to sub-divide the Holocene into three ages and determine where to place the so-called “golden spike” at those points where these three sub-divisions occur.
The golden spike — technically known as the Global Boundary Stratotype Section and Point, or GSSP — is an internationally agreed upon reference point that determines the lower part of a stage, which are rock layers laid down in a single age.
Now, the Early Holocene Greenlandian Age; Middle Holocene Northgrippian Age; and Late Holocene Meghalayan Age have their own individual golden spikes.
“The terms early, middle and late Holocene have long been in use, but they’ve never been formally defined,” says Head, adding that a lack of formal definition created some confusion among experts.
“This is the job of the subcommission, to provide order where none existed before,” he says.
The Holocene Epoch stretches back to about 11,700 years ago in Earth’s history. It is characterized by events of both warming and cooling temperatures and the resulting changes to sea levels and land masses.
Rock layers in the Holocene contain sediments from ancient sea floors, lake bottoms, glacial ice and a mineral called calcite, giving researchers many clues as to the occurrence of climate-change related events during the Holocene’s three sub-divisions.
Head says his subcommission’s formalizing of the three ages solidifies scientists’ knowledge of the Holocene and explains in particular the fall of several civilizations some 4,200 years ago.
“This event brings together the convergence of global climatic change, archaeological evidence, historical records and societal evolution,” he says. “We’re bringing all this together to form a coherent story that is now reflected in formal geological time. We’re revealing the whole picture here.”
Head says the Geological Time Scale not only “reflects a narrative of how we understand Earth history,” but also illuminates “the history of humans, and so their story also becomes entwined with the geological record and geological time, and that’s very exciting.”
The past also sheds light on present trends. Head says the massive flooding that took place 8,200 years ago at the start of the Middle Holocene Northgrippian Age serves as a “warning shot” of how contemporary human-induced climate change can exacerbate melting of ice in the high northern latitudes, causing ocean currents to shift and extreme weather to result.