2023-07-21 04:00:10
Nuclear weapons testing in the 1950s and early 1960s left the first indelible marks of human activity on Earth, potentially ushering in a new geological era, the Anthropocene, geologists say.
Plutonium-239 has spread all over the planet.
Credit: Galerie Bilderwelt
The fallout from these nuclear tests deposited layers of sediment enriched in radioactive plutonium-239, trapped in the earth. It is this radioactive imprint that could mark the beginning of the Anthropocene.
According to Colin Waters, honorary professor at the University of Leicester and chairman of the Anthropocene Working Group (AWG), this precise geochemical layer, present in all environments, helps define the boundary (A boundary is an imaginary line separating two territories, in particular two…) of this new geological epoch.
The concept of the Anthropocene was proposed in the early 2000s by the Dutch meteorologist Paul Crutzen, winner of the Nobel Prize in Chemistry in 1995. According to him, the Anthropocene would begin with the industrial revolution and the invention of the steam engine 1784.
However, this demarcation is invisible outside of Europe, the center of industrialization in the 18th century (A century is now a period of one hundred years. The word comes from the Latin saeculum, i, which…). The sediments of the southern hemisphere (The southern hemisphere or austral hemisphere is half of the terrestrial globe…) show no significant effect of this industrial revolution.
In contrast, the fallout from plutonium-239 is visible all over the world. It was on this basis that the AWG chose Crawford Lake in Ontario to mark the end of the Holocene and the beginning of the Anthropocene.
Formed 10,000 years ago by the collapse of a limestone cave, Crawford Lake has a shape that prevents the mixing (A mixture is an association of two or more solid, liquid or gaseous substances…) of surface waters (A surface generally designates the superficial layer of an object. The term a…) with the lower layers. Thus, the lake acts as a funnel for particles falling through the water column.
According to Francine McCarthy, professor of Earth sciences at Brock University in Canada and member of the AWG, it is in these white layers that we can precisely identify each year. Thus, measurements at Crawford Lake indicate that 1950 is the point (Graphic) where Earth systems were “overwhelmed” by human activity, propelling an era “geologically different (In mathematics, different is defined in algebraic theory of…) from that before”.
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