Alejandro Cearreta
Paleontologist at the University of the Basque Country UPV/EHU, director of the geology department and member of the former Anthropocene Working Group
The Anthropocene Working Group (AWG) was established by the Subcommission on Quaternary Stratigraphy to determine the validity of the Anthropocene as a new geological time and to propose its definition. Over the past 15 years it has evaluated physical, chemical and biological evidence preserved in the most recent sediments and rocks of our planet. Since 2019, a collaborative project between the AWG and the Haus der Kulturen der Welt and the Max Planck Institute for the History of Science (Germany) has been underway to analyse the most suitable sites that could host the stratotype marking the beginning of the Anthropocene. Most of the teams that submitted their proposals identified plutonium as their main indicator and proposed the start of the Anthropocene based on an increase in the signal of this (mostly) man-made radioactive element, found in sediments and rocks deposited across the planet since the early 1950s.
The AWG has finally selected Crawford Lake (Canada) as the site containing the reference sedimentary record to define the beginning of the Anthropocene. The sediments that accumulate at its bottom are formed by annual layers called lake varves. The layer proposed as a marker for the Anthropocene stratotype is found in a calcite sheet deposited in the summer of 1950 and was selected because of the rapid increase in plutonium thereafter. This signal also coincides with an increase in spheroidal carbonaceous particles (originating from the burning of fossil fuels at high temperatures) and a major ecosystem change identified by a decline in elm pollen and a replacement in the diatom species living in the lake.
The Anthropocene is part of geological time and, despite its short duration, will be recognised as the end of a relatively stable epoch in Earth's history, driven by an unprecedented increase in human population, energy consumption, industrialisation and globalisation following the end of World War II.