Did nuclear fallout begin the Anthropocene Age?

Eric Hopton for redOrbit.com – Your Universe Online

Is the “Nuclear Age” also the start of a new chapter in Earth history: the beginning of the Anthropocene Epoch? An international group of scientists believes it could be. They have proposed that fallout from hundreds of nuclear weapons tests in the late 1940s to early 1960s could be used to mark the dawn of the new geological age.

The study was led by Dr. Colin Waters of the British Geological Survey and is published in the Bulletin of the Atomic Scientists.

Driven underground

When the 1945 Trinity device was detonated in New Mexico, fallout was initially fairly localized. But, by 1952, fallout from the much larger “thermonuclear” or “hydrogen” weapons tests dispersed over the entire Earth surface. Fallout peaked in 1962, the year before the Partial Nuclear Test-Ban Treaty which drove most nuclear detonations underground.

The 1952 rise in abundance of the isotope plutonium-239 is preferred as a marker for several reasons. It is rare in nature and is a significant component of fallout. It is also relatively immobile in sediments, and has a long half-life (so will persist long into the future).

The rise is broadly coincident with the onset of the mid-twentieth century “Great Acceleration” when human population growth, economic development, and industrialization all expanded rapidly. The emergence of megacities, using huge quantities of concrete, is coincident with earth movement on a vast scale. Mineral exploitation has resulted in the generation of marked geochemical signatures across the globe and this age of hydrocarbon burning has resulted in greatly increased carbon emissions. Humanity’s modification of the planet has caused an increase in species extinctions and invasions. All these features are being expressed in the sediments accumulating across the planet and will be recognizable to the geoscientists of the far future.

They pose the question, says the AWG, “If the sum of these changes is a recognition that we now live in a new epoch, the Anthropocene, how can we define when it started?”

Standard practice for defining geological time units is to identify a single reference point (or “golden spike”) which fixes the lower boundary of the time unit within a succession of rock or sediment layers. The boundary should be characterized by a signature that is both rapidly developed and wide-spread. The AWG proposes that the program of atmospheric nuclear weapons testing may have generated such a signature.

The 100,000 year legacy of plutonium

Dr. Waters said: “It is sobering to think that the actions of humanity over a few short years in the mid-20th century created such large amounts of artificial radionuclides that scattered across the Earth as fallout, producing a signal in modern strata that, in the case of plutonium, will be a detectable for about 100,000 years into the future.”

Professor Zalasiewicz said, “Human beings don’t merely inhabit the world. They alter it, on an increasingly epic scale.”

In 2016, the Anthropocene Working Group hopes to make recommendations on whether this new time unit should be formalized and, if so, how it might be defined and characterized.

—–

Follow redOrbit on Twitter, Facebook, Google+, Instagram and Pinterest.

redOrbit.com
offers Science, Space, Technology, Health news, videos, images and
reference information. For the latest science news, space news,
technology news, health news visit redOrbit.com frequently. Learn
something new every day.”