NOEL KING, HOST:
Did you know that we are living in a distinct new geological time period? Welcome to the Anthropocene. Here's NPR's Rebecca Hersher.
REBECCA HERSHER, BYLINE: Humans have changed the planet in a lot of ways. That's where the idea of the Anthropocene Epoch comes from - anthro, Greek for human. Nicholas Kawa is an anthropologist at Ohio State.
NICHOLAS KAWA: There's lots of different debates about the Anthropocene and where it starts. There are some people that see an old Anthropocene that could go all the way back to when we see humans, you know, controlling and using fire like a hundred thousand years ago.
HERSHER: Others feel like the turning point was when humans started large-scale agriculture.
KAWA: And then there's another camp that sees it as occurring more recently with industrialization. And so I think there's kind of an old Anthropocene and a new Anthropocene.
HERSHER: Many of the scientists who are focused on the new Anthropocene are geologists because industrialization is really when you start to see a clear line or layer in the rock that says humans were here. There are chemicals, tiny bits of plastic, carbon and nitrogen from burning fossil fuels, even radioactive elements from nuclear blasts, all of which get into mud and soil and ice and end up being part of the geological record. Simon Turner is one of the leaders of the Anthropocene Working Group, a group of scientists who are trying to officially define the start date for the Anthropocene.
SIMON TURNER: It's like a dream job.
HERSHER: In his actual job at University College London, Turner studies how humans affect aquatic systems like lakes. But right now, he's spending a lot of time helping groups of scientists all over the world look for what's called a golden spike location. Every geological time period has one of these reference spots somewhere on Earth that perfectly captures what makes that period unique. Usually, it's a distinct layer of rock in a cliff or maybe in an ice core, like debris from the meteor that killed the dinosaurs. That layer is really obvious at this one place in Tunisia.
TURNER: The idea of a golden spike is you have this series of markers of the Anthropocene.
HERSHER: Turner is coordinating a global effort to find this perfect spot. Right now, there are 11 potential sites on five continents - an Antarctic ice core, bays in the U.S. and Japan.
TURNER: So sequences of mud, of coral, of stalagmites in caves.
HERSHER: Peat bogs in Europe, a lake in China. One of the sites is a reservoir in California. It was built in the late 1800s, and it's special because a ton of sediment has collected at the bottom over the years.
ALLISON STEGNER: And at this point, there's over 11 meters of sediment since 1892.
HERSHER: Allison Stegner is a geologist at Stanford who's leading the golden spike team for the reservoir. Her team has removed a three-story-tall, 127-year-old cross section of the mud in the reservoir. And they're looking for evidence of humans, especially radioactive elements and evidence of burning fossil fuels.
STEGNER: We can actually look at what happens seasonally over the last 127 years, which is really, really rare.
HERSHER: Stegner's team might be able to pinpoint the beginning of the Anthropocene down to a specific year. And although the analyses are not finished, this team and others seem to be zeroing in on the year 1952 or so. That's when big thermonuclear tests spread radioactive material around the world, which would mean that some baby boomers are literally older than the Anthropocene. It also means that the age of humans will likely be defined by some of humanity's most destructive actions. Nick Kawa, the anthropologist, says it's important to reflect on that.
KAWA: You think of so many nasty facets of human history that we like to kind of sweep under the rug. And it could actually be helpful in the sense that like, OK, we're using an atomic bomb to define the human era. What does that say about us? And what do we want future markers to look like?
HERSHER: The Anthropocene Working Group expects to wrap up work on all 11 potential golden spike sites by summer 2022.
Rebecca Hersher, NPR News.
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