PHOTO: MAREK DOBROWOLSKI562 6 MAY 2022 • VOL 376 ISSUE 6593 science.org SCIENCEI
f you had to pick one spot that best re-
flects when human activity became an
Earth-shaping force, where would it be?
Geoscientists will consider the question
this month when they meet to evaluate
12 sites, only one of which can serve as
the “golden spike” for the Anthropocene, a
proposed geological age beginning in the
1950s amid the fire of nuclear bomb tests and
the fumes of surging fossil fuel use.
Although the idea of the Anthropocene has
gained wide traction, it still lacks a formal
geological definition. In 2016, the Anthro-
pocene Working Group (AWG), a group of
several dozen geoscientists convened by the
International Commission on Stratigraphy
(ICS), settled on the early 1950s as its starting
point (Science, 26 August 2016, p. 852). But
the ICS still needs a formal proposal with an
ideal geologic sample recording these global
changes—a golden spike—to mark the end of
the Holocene epoch, which began 11,700 years
ago, and the beginning of the Anthropocene.
To find that sample, teams of earth scien-
tists spent several years analyzing sites that
contain promising markers, such as spikesin plutonium and other radionuclides that
settled after atmospheric nuclear tests,
spherical ash particles from unchecked
industrial emissions, microplastics, and
perturbations to carbon and nitrogen
chemistry from greenhouse gas emissions
and urban smog. The array of possibilities
was bewildering, says Colin Waters, a geo-
logist at the University of Leicester and
AWG chair. “Starting from scratch, you’ve
got the whole world to play with.”
At a meeting in Berlin, starting on
18 May, the teams will present the case
for their site to serve as the golden spike.
Months of deliberation will begin this sum-
mer, before a final silent voting period. If
60% of the group’s members agree on one
site, a selection will be announced by De-
cember, Waters says.
Some of the strongest candidates come
from lake bottoms that accumulate muds in
thin annual layers, creating high-resolution
records. Crawford Lake in Canada’s Ontario
province, only some 200 meters wide but
2 5 m e t e r s d e e p , i s o n e. In c o r e s o f m u d f r o m
t h e l a k e , c h a n g e s s e e n s i n c e t h e 1 9 5 0 s s t a n d
out vividly, including the bomb spike and an
“off the charts” increase in soot from localindustry, says Francine McCarthy, a micro-
paleontologist at Brock University. “We
have a really ideal site,” she says.
A site outside Europe or North Amer-
ica, which industrialized well ahead of
other regions, might be a better record of
changes that swept the world in the 1950s,
says Yongming Han, a geochemist at the
Chinese Academy of Sciences’s Institute of
Earth Environment. His team will propose
Sihailongwan Lake, in a protected forest in
northeastern China. Mud cores from the
lake show not only the bomb spike and
rises in soot, but also increases in spherical
ash particles and heavy metals. They also
record a rapid increase in light carbon, the
isotope favored by life, driven by burning
fossil fuels that were once organic matter.
There is no greater aggregator of global
signals than the ocean, making marine
sediments strong contenders. One set of
muds, collected in the Baltic Sea, shows
a pronounced change from light gray to
dark brown in the 1950s, the result of al-
gal blooms fed by fertilizer in farming run-
off. “There’s an explosion” of algae, says
Jérôme Kaiser, a marine geochemist at the
Leibniz Institute for Baltic Sea Research.IN DEPTH
Peat layers in Poland’s Śnieżka bog capture spikes in plutonium from nuclear tests, jumps in metals from nearby smokestacks, and the extinction of native amoebas.By Pa u l Vo ose nG E O L O GYBids for Anthropocene’s ‘golden spike’ emerge
Sites compete to mark global changes of the 1950s and define new geological age
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