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A small lake outside Toronto could be the clue that a new epoch has begun on Earth

ADRIAN FLORIDO, HOST:

Are we living in a new epoch in Earth's geologic history? A few years ago, a group of scientists proposed that, yes - that humans have so altered the planet that we have left the Holocene epoch and are now living in the Anthropocene epoch - anthro for humans. To make this case, they had to find a spot on Earth that best preserved the evidence of the indelible impact that humans have had on the planet, and now they say they found it. It's a small lake outside Toronto. Francine McCarthy, a professor of earth sciences at Brock University in Ontario, led the research group. Welcome.

FRANCINE MCCARTHY: Happy to be here.

FLORIDO: So first, what does this lake, Crawford Lake, tell you about humans' influence on the planet?

MCCARTHY: So it is the sediments of that small lake that record things like the atmospheric pollution, particularly from the combustion of fossil fuels. It records the testing of nuclear weapons during the Cold War. It records everything that went on, on a yearly basis. Each layer is distinct from the one that was deposited the year before, like tree rings, so we can actually sample individual years of sediment and measure all sorts of aspects of that sediment to reconstruct what the world was like in 1945 or 1950 or 1955. And we know that dramatic changes happened in the early 1950s - not just at Crawford Lake, all around the world, but recorded there best.

FLORIDO: You hinted at this, but when do you and your team consider this new epoch to have begun - the Anthropocene epoch?

MCCARTHY: Literally the year 1950 is what we've suggested.

FLORIDO: Well, not all scientists are in favor of establishing this new geologic epoch. Some point to the fact that other epochs haven't been named until thousands of years after they occurred. Is the last several decades enough - you think? - to constitute an epoch when others have been defined by millennia, by such - by much longer time spans?

MCCARTHY: That's certainly a question that we've gotten. I think what we respond is it's not how long the planet has been different that should matter to put a line on the timescale and identify a new epoch. It is how different the environment of the planet is from what it used to be. The lines on the geologic time scale are there to illustrate when massive things happen, like when the asteroid hit the planet and the dinosaurs and a bunch of other things became extinct. That's a pretty obvious big thing. It deserves a really big line on the timescale, and that includes an era as well as the epoch and period and so on. So it is what happened then. It's not that it was 66 million years ago that matters. It's that massive changes happened to the entire planet.

FLORIDO: So what happens next, Professor? What has to happen to make this new epoch official?

MCCARTHY: We're going to write up our proposal that's going to include data from Crawford Lake and a few of the other sites that we studied along the way to make that strong case that the Earth system has shifted to the point that a new line on the timescale needs to be drawn. It's not our responsibility to do that, so we'll submit the proposal to the group that has that responsibility. They will assess the evidence, and they will make a decision - yes or no. But either way, whether there is a new line on the timescale or not, opening up this conversation the way our activity has done in the last five years looking for evidence of this major shift - I think that is the most important thing that we've done - to get people talking about this.

FLORIDO: Well, I've been speaking with Francine McCarthy of Brock University in Ontario, Canada. Thank you for joining us.

MCCARTHY: Thank you.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.

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Adrian Florido
Adrian Florido is a national correspondent for NPR covering race and identity in America.
Marc Rivers
Christopher Intagliata is an editor at All Things Considered, where he writes news and edits interviews with politicians, musicians, restaurant owners, scientists and many of the other voices heard on the air.
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