A lake in Ontario, Canada with water so still and undisturbed that its sediment layers provide an exceptionally clean record of environmental changes. Scientists proposed it as the official reference point for marking the start of the Anthropocene, the epoch defined by human impact on Earth.
Laslovarga, CC BY-SA 3.0, via Wikimedia Commons
A geological time capsule
Crawford Lake is a rare type of lake known as meromictic, meaning its layers of water do not mix. The lake occupies a deep sinkhole on the Niagara Escarpment, with a surface area of only 2.4 hectares but a depth of 24 meters. This high depth-to-surface ratio prevents wind from disturbing the water column. The bottom layer, or monimolimnion, is isolated from the upper layers and the atmosphere, creating an oxygen-free environment where sediment can settle without being disturbed by currents or burrowing organisms.
Each year, seasonal changes cause distinct layers of sediment, called varves, to form on the lakebed. In the summer, higher temperatures lead to the precipitation of calcite crystals, which create a light-colored layer. This is followed by a darker layer of organic matter that settles during the rest of the year. The resulting varves create a perfectly preserved, year-by-year timeline of environmental conditions, like tree rings. This exceptional record allows scientists to pinpoint specific dates in the Earth's recent past.
Pinpointing the Anthropocene
In July 2023, the Anthropocene Working Group (AWG) selected Crawford Lake from 12 candidate sites as the proposed Global Boundary Stratotype Section and Point (GSSP), or "golden spike," for the Anthropocene epoch. The GSSP is a physical reference point marking the beginning of a new chapter in the planet's geological timescale. The main marker identified in Crawford Lake's sediment is a sharp spike in plutonium-239, a direct result of above-ground thermonuclear bomb tests in the early 1950s. This global fallout is a clear and datable signal of humanity's planet-altering capacity.
The plutonium spike coincides with the "Great Acceleration," a mid-20th-century surge in human population, industrial activity, and resource consumption. The lake's varves also record this surge through other signals, including spherical carbonaceous particles (fly ash) from high-temperature fossil fuel combustion.
The proposal to formalize the Anthropocene epoch beginning around 1952, using Crawford Lake as the reference point, was a major step after 15 years of research by the AWG. However, in a contentious series of votes concluding in March 2024, the proposal was ultimately rejected by the International Union of Geological Sciences (IUGS). Geologists cited the very short time span of the proposed epoch and the long history of human impacts, from early agriculture to the industrial revolution, as reasons for the rejection. While the Anthropocene is not an official epoch, the term is a widely used concept to describe the current period of human-dominated environmental change.
💡Fun Facts
The discovery that first brought scientists to the lake in the 1970s was corn pollen in the sediment, which led to the excavation of a 15th-century Wendat or Attawandaron village nearby.
Sediment cores are extracted using a "freeze corer," a metal tube filled with dry ice and alcohol that is plunged into the lakebed, freezing the layered sediment to its outer surface.
The lake's Indigenous name in the Wendat language is "Kionywarihwaen," which translates to "where we have a story to tell."
Evidence of Indigenous agriculture from the 13th to 15th centuries changed the lake's chemistry, initiating the clear annual varve formation that scientists study today.
Park open year-round, hours vary by season. Check the official website for current times.
Admission
Reservations are recommended to guarantee entry and save on gate fees. See website for current pricing.
Accessibility
The conservation area has a boardwalk that loops around the lake. The boardwalk was temporarily closed for reconstruction starting in late 2025 with an expected completion in 2026.
