833. Towards a Definition of the Anthropocene

Tens of thousands of years ago, human hunting and gathering activities had little long-term impact on the environment. In contrast, today's humanity leaves indelible footprints on the Earth, whether through large cities, massive agriculture, deforestation, or the exposure of the Earth's sediments to industrial pollution, the spread of residual radioactive materials from nuclear testing, and extensive deforestation.

Some have declared that we live in the Anthropocene. The Anthropocene is a hypothetical geological epoch proposed to mark the beginning of humanity's profound impact on Earth's geology and ecosystems. The term was first used in 2000 by Paul Crutzen, a Dutch atmospheric chemist who won the Nobel Prize in Chemistry in 1995 for his research on the ozone hole. It marks the beginning of a debate about how human activities in the modern era have the potential to shape a new geological epoch. Over time, this concept has taken hold in Earth system science, redefining processes of global change that alter conditions typical of the Holocene. Initially, the Anthropocene was associated with the rise of greenhouse gases, particularly carbon dioxide and methane, since the late 18th century following the Industrial Revolution in the United Kingdom. However, further research has linked the Anthropocene to the "Great Acceleration" since the mid-20th century, a period of rapid socio-economic change when human activities began to have significant impacts on Earth's systems.

However, the definition of the Anthropocene has not yet been settled among researchers. In mid-July, after more than a decade of work by geologists, a layer of sediment at the bottom of Lake Crawford in Ontario, Canada, was announced as a candidate for the Global Boundary Stratotype Section and Point (GSSP) that represents the Anthropocene.

According to articles in Nature and PNAS, Lake Crawford covers only 2.4 hectares and is 24 meters deep. The water in the deepest part does not mix with the surface water, resulting in the annual formation of distinct layers of sediment on the lake's surface. The lake is a naturally formed sinkhole in limestone terrain, with the deepest part containing slightly saline and highly alkaline water, creating chemical conditions that prevent the survival of organisms that could disturb the sediment at the bottom of the lake. The undisturbed sediment layers have recorded traces of human activity in chronological order, much like tree rings. For example, the sediment indicates a sharp increase in plutonium content since the late 1940s due to nuclear testing. In addition, the presence of spherical carbonaceous particles (SCPs) in the sediment reflects the significant increase in global fossil fuel consumption during the 1950s.

However, defining a new geological epoch is unprecedented, and experts must debate whether Lake Crawford should be officially designated as a "golden spike," the boundary marker for geological epochs that is a golden stake driven into an internationally designated standard geological section. The Anthropocene Working Group (AWG) narrowly achieved a majority vote in favor of Lake Crawford, but formal approval as a reference point will require expert evaluation. In addition, there is an ongoing debate among experts about whether the impact of human activity on the Earth's environment has been preserved in the geological record since the beginning of agriculture over 12,000 years ago, leading to discussions about whether the beginning of the Anthropocene should be placed in the 1950s.
 

References
Sid Perkins. Researchers move closer to defining the Anthropocene, PNAS July 12, 2023. 
120 (29) e2310613120 https://doi.org/10.1073/pnas.2310613120

Alexandra Witze. This quiet lake could mark the start of a new Anthropocene epoch
The dawn of a new geological epoch is recorded in the contaminated sediment at the bottom of Crawford Lake in Canada. Correction 12 July 2023 Nature 619, 441-442 (2023)　doi: https://doi.org/10.1038/d41586-023-02234-z

Contributor: IIYAMA Miyuki (Information Program)