For historians, the first atomic bomb blast in 1945 ushered in the nuclear age. But for a group of geologists, the 16 July test near Alamogordo, New Mexico, marks the start of a new unit of geologic time, the Anthropocene epoch.
The term Anthropocene was coined 15 years ago to mean the age of widespread human influence over the planet. Ever since, geologists have debated when people first left a clear mark in the rock record, and whether to enshrine that moment as the start of a formal slice of geological unit. Some researchers have proposed setting the beginning of the Anthropocene — and the end of the current epoch, the Holocene — at the start of the Industrial Revolution, or even further back to the dawn of agriculture. Others look to the vast expansion in human activity in the second half of the 20th century.
Now a group of international scientists has thrown its weight behind the latter possibility and suggested using the first nuclear blast as a starting point. “It’s a well defined spot in time — it’s a big historical event,” says Jan Zalasiewicz, a stratigrapher at the University of Leicester, UK, and lead author of the paper published this week1.
Zalasiewicz wrote the study with 25 other members of a stratigraphic working group that is exploring whether to formally define the Anthropocene. In their paper, the researchers propose to define the boundary by tracking the presence of radioactive elements that spread around the globe from the first A-bomb test in 1945 and the much larger nuclear blasts that took place over the next decade.
The appearance of these radionuclides, such as long-lived plutonium-239, coincide more or less with many other large-scale changes that humans wrought in the years just following World War II. The mass production of fertilizer doubled the amount of reactive nitrogen in the environment, and the concentration of carbon dioxide in the atmosphere started to surge. New forms of plastics went into mass production and spread around the globe, and increasing global commerce carried invasive animal and plant species between continents. And migrations from rural areas to urban centers picked up speed, feeding the growth of megacities. This time has been called the Great Acceleration.
Other researchers argue for a different start of the Anthropocene. Last week, Matt Edgeworth, an archaeologist at the University of Leicester, and five other members of the Anthropocene working group proposed defining that boundary as the transition between natural geological deposits and ones altered by humans, such as layers of pottery-filled debris in archaeological sites or soils that had been plowed for agriculture2.
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