Short Wave - Debating When The 'Age Of Humans' Began

Episode Date: April 12, 2021

Humans have changed the Earth in such profound ways that scientists say we have entered a new geological period: the Anthropocene Epoch.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

Hey, everybody, Maddie Safai here with Emily Kwong. Hey, Maddie. So, Emily, we have put out more than 350 episodes of shortwave since we launched this show. I am so proud and so tired. I feel you. I feel you. And, you know, obviously, the coronavirus has gotten a lot of our attention. But after that, can you guess what topic we've covered the most and our listeners love? I don't know.

I feel like all you talk about is bugs. Okay. Wow, wow, wow, wow. No, it's climate and the environment. Oh, yeah, of course. It's one of the biggest stories of our lifetime. Which is why we're dedicating this whole week to stories about climate change. Starting today with a new episode about the debate over defining when humans really started impacting the planet. Oh, yeah, we're philosophizing over here. And then we're bringing back some of our favorites. Like that episode about the slow creep of sea level rise in the U.S.

And what the East Coast might look like in 2045. Ooh, that was a good one. Plus, another one on the Supreme Court case going on right now over who should pay for climate change. And we followed some of the activists putting their lives at risk to protect the planet. So tune in all this week. You're listening to Shortwave from NPR. Hi, Maddie. Hi, Rebecca Hersher.

So today I want to talk about the Anthropocene. Have you ever run across that term? Yes, I have. Kind of. I can tell from your tone that you don't want to elaborate. No, no, no, go ahead. So the Anthropocene refers to the age of humans. And it's the part of Earth's history that we're living in right now. It's primarily defined by the impacts that humans have on the planet. Ooh, human impacts on the planet very appropriate for Climate Week. Becky, go on.

Yes. So the word Anthropocene, it was popularized about, 20 years ago by an atmospheric chemist, but it's not an official geological time period yet. Okay, why not? Because we don't know when it started. Like, when would you guess that humans began really affecting the planet? Like maybe, like, mass agriculture, question mark? Sure, yeah, no, that's a totally reasonable answer. Here are some other reasonable answers.

When humans started burning fossil fuels, or when colonialism began, or when humans, started setting off atomic bombs. So scientists, specifically geologists, they've been trying to agree on one starting date. And they've been working on this for years. They're getting pretty close. And so the work is really starting to heat up. So today on the show, when did the Anthropocene begin? And who gets to decide?

I'm Maddie Safaya, and this is Shortwave, the Daily Science Podcast from NPR. Okay, Becky, let's talk about the Anthropocene. What are the leading contenders for the starting date of this age of humans? Well, it depends on who you ask. You know, for example, if you ask an anthropologist or social scientists, they're likely to have a different answer than a geologist or a stratographer, people who specifically study geologic time by looking at how rocks are layered. There's lots of different debates about the Anthropocene and where it starts. That is Nicholas Kewa. He is an anthropologist at Ohio State.

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. Other people feel like the turning point was when humans started large-scale agriculture, maybe a couple thousand years ago. Many indigenous scholars feel that the age of humans began when colonialism started, like in the 15th century and Europeans systematically disrupted people and land all over the world. And then there's another camp that sees it as occurring more recently with industrial. realization. And so I think there's kind of an old Anthropocene and a new Anthropocene. Okay. Okay. So anthropologists, historians, they are arguing for an old Anthropocene. So like basically starting earlier. Right. Who's arguing for the new Anthropocene that starts more recently? The geologists, they are the ones who will get to make the official decision. And it makes sense

that they'd be looking more recently when you think about what geologists care about. They care about rocks, among other things, rocks, right? Yeah. Totally. Geologists care about rocks. And industrialization, late 1800s, early 1900s, that's really when you start to see a clear line or layer in the rock that says humans were here. There are chemicals, there are tiny bits of plastic, carbon and nitrogen from burning fossil fuels. You even start to see radioactive elements from nuclear blasts. And all that stuff gets into the mud and soil and ice and ends up being part of the geological record.

And Becky, why does it matter to geologists like to find, a line in the rock? Because in order for the Anthropocene to be an official geological time period, the world's geologists need to agree on a line in the rock or ice or mud that scientists can find almost anywhere in the world. Okay, okay. So it's important that you can find the line kind of everywhere. Exactly, yeah. And you need one reference point for that line. And that point in time, the place that epitomizes it, it's called the Golden Spike location. Every geological time period has one of these reference spots somewhere on Earth that perfectly captures what makes that period unique. Ooh, I didn't know that, Becky. Okay, so give me like a golden spike example.

So the golden spike location that defines the end of the age of dinosaurs is a good example. So, you know, a meteor hit Earth around that time. It made impact in what is now Mexico, and it sent debris all around the world. And you can see that layer of debris in rock or in ice. But the place where the layer is most obvious is this one place in Tunisia, really far from Mexico. And so that location is the golden spike location for the end of the age of dinosaurs. So that's what geologists are looking for. A golden spike location, but for the Anthropocene. And when they find it, they'll be able to say exactly when the age of humans began?

Exactly. Okay, so what are places that are contenders for this new golden spike? So right now, there are 11 potential sites. on five continents. There is an Antarctic ice core. There's mud at the bottom of bays in the U.S. in Japan. Peat bogs and stalagmites and caves in Europe. Mud from the bottom of a lake in China.

Okay, so Herscher, I'm hearing maybe more mud than I was expecting, like a lot of muddy options. Yeah. It sounds like, is that right? Yeah, totally. And I talked to the lead scientist at one of these mud sites. It's a reservoir in California. And basically the dam. for this reservoir was built in the late 1800s, the goal was to hold water. But really, what this

reservoir has been great at collecting is sediment. And at this point, there's over 11 meters of sediment since 1892. That's Allison Stegger. It's a lot. So she's a geologist at Stanford and the leader for the Golden Spike team at this reservoir. So why is it so good to have so much mud to work with? Well, you can think about the mud like a diary for the reservoir. So like every winter when it rains, a lot of sandy sediment washes into the lake. And the next summer, when it's warm, a lot of plants grow in the lake, and then they die, and their plant carcasses sink to the bottom of the lake. In the next winter, there's more sandy bits.

And then the next summer, there are more plant bits. When we have a lot of sediment in a site like this, it gives us the ability to study what happened in the past at really fine resolution. And maybe there are other things that end up in the mud along the way, right? Like tiny pieces of plastic or chemical residue, even radioactive elements. So you can use the layers in the mud to figure out exactly when those human-made things showed up. So how exactly did this scientist and her team do that? I mean, it seems like kind of difficult to scoop the mud out of the bottom of this lake without messing with the layers. You know what I mean?

It's mud. Yeah, no, it's really hard. So they had to use a machine called a vibracore, which this is a fun fact. I thought it was fun. It's similar to what construction workers use to shake the bubbles out of cement. It vibrates really, really fast. And you can use it to push a pipe vertically down into the mud and then carefully remove that cylinder of sediment a few feet at a time. So in all, they've removed a three-story tall, 127-year-old cross-section of the mud.

Wow. And they've scanned it for evidence of fossil fuel combustion, for radioisotopes that get deposited when nuclear bombs go off, and a host of other evidence of humans. And now they're preparing their final argument, you know, laying out all their evidence saying when they believe the Anthropocene began, according to their mud. And what's the answer, according to mud? Well, Stegner's team is still working, as are the other 10 teams. They're on track for a final decision around 2023. But there are hints about what the final answer will be. So the whole effort is being coordinated by the Anthropocene Working Group, which is an international group of geologists.

And they say it's looking like the official beginning of the Anthropocene will probably be in the early 1950s. 1950s? That's like recently, recently. And also, why the early 1950s specifically? Like humans started burning fossil fuels and manufacturing things a lot earlier than that, right? Right. I had the same question, but those things didn't leave markers in the rock and mud and ice all around the world. Remember, it has to be everywhere. Right. What did leave markers all around the world is nuclear blasts. Oh, okay. First of all, that's depressing. Second of all, didn't people start setting off atomic bombs in the 40s? Like, why do they say it starts in the 50s, Becky? So the answer has to do with the size of the bombs, at least according to Colin Waters. He's the chair of the Anthropocene Working Group.

And it's not really until you get to about 1952 with the big thermonuclear destinations that you start to see these reginaluclides appearing everywhere. So, yeah, the exact date won't be official for another couple years. But it looks like people who were born in the 1940s were probably, technically, born in a different geologic period. Nothing makes you feel old by being from another epic. You know what I'm saying, Becky? But, okay, okay, indulge me for a moment. Is that really the best geologists can do?

Like, we're going to define the age of humans based on one of the most destructive acts of people. See, now you're thinking like an anthropologist. And those are really valid questions. So Nick Kewa, the anthropologist at Ohio State, has thought about this a lot. Where we see the starting point of the Anthropocene tells us a lot about how we see humanity. So one thing that makes him a little queasy about the mid-century start date is that it ignores everything that came before. You know, there's so much human history that just gets wiped away once the golden spike. location is chosen and the date is made official.

So I think if we just look at the atomic bomb or whatever, we're ignoring this long lead-up that is linked to long histories of environmental degradation led by, you know, colonial powers and by, to be frank, market capitalism. He also said something that I think is really interesting because I also heard it from geologists. And that's that the Anthropocene is different. It's just different from other geological time periods. And that's because it comes with moral baggage. You know, K.W. said something that was really funny to me.

He was talking about the meteor that helped finish off the dinosaurs. And he said, you know, we don't think about meteors in ethical terms. They just happen. Yeah, yeah. I get it. Atomic bombs and deforestation and extracting, burning oil and gas. Humans do those things. And some humans do a lot more than others.

Yeah, exactly. And there are questions of responsibility. of right and wrong. It's honestly kind of uncomfortable, but it can also be good. You know, if atomic bombs become the ultimate marker of humanity on Earth, Kewa says we should all take a moment and think about what that means. I think it's good for us to take ownership of that. And 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, okay, we're using an atomic bomb to define the human era. What does that say about us? And what do we actually, what do we want future markers to

look like, you know? All right, Becky Herscher, that is a lot to think about. This was really interesting. Thank you so much for bringing on the show. Yeah, of course. Happy Climate Week. Happy Climate Week. That's nice. This episode was produced by Britt Hansen, edited by Giselle Grayson and fact-checked by Rasha Reedy. The audio engineer for this episode was Josh Newell. I'm Maddie Cefat. and you're listening to Shortwave, the Daily Science Podcast from NPR.