There’s a new kind of rock in town.

And it’s made– of trash? They’re partly formed from melted plastic,   and were first identified by scientists in  Hawai’i, who published their findings in 2014.

In the decade since, they’ve turned up in 11  different countries on at least 5 continents. They’ve even been found on a remote island off  the coast of Brazil where no one lives full-time. If it weren’t for humans, plastic  rocks wouldn’t even be a thing.

And they’re just one of many  signs that we’re transforming   the Earth in ways that could easily outlast us. The question is: can we undo what we’ve done? Hi!

I’m Sage, and this is Crash Course Geology. [THEME MUSIC] As we’ve learned in this series, our  planet’s rocks hold a record of its past. Geologists figure out when different geological   events happened through stratigraphy: the  study of Earth’s rock layers, or strata. So… a million years from now, if some  future society looked at the stripey   layers of rock from our time…  what would they learn about us?

In the grand scheme of Earth’s  roughly 4.6 billion years,   you and I and all the humans who ever  lived just showed up to the party. Like, say my arm represents our planet’s  entire existence, starting at my shoulder. The time range where humans have spread out  around the world— the past 12,000 years or so?

That’s like the tiny slice  at the end of my fingernail. From a geologic perspective, we’re a blip. But there’s no denying we’ve made a splash.

Between all our mining, building, plowing,   and paving, we’ve transformed at least  83 percent of Earth’s land surface. With every passing year,   we move 24 times more sediment than  all the rivers in the world combined. And all that has consequences, from  increased air and water pollution to   wiping out animal populations at an alarming pace.

What’s more, we pump massive amounts  of carbon dioxide into the atmosphere,   by burning fossil fuels to power  our societies and industries. In just a couple hundred years,   our fossil fuel use has caused the  climate to warm at a super fast rate. It’s triggering the melting of glaciers,   causing sea levels to rise, and increasing  the frequency of extreme weather events.

But if humans are a blink of an  eye in the geologic timescale,   are we really that big of a deal? Could we cause as much irreversible destruction  as, say, the asteroid that killed the dinosaurs? Well it turns out, geologists  don’t really agree on that.

Let me explain. A group of geologists called  the International Commission on   Stratigraphy is in charge of defining  different chunks of geologic time. One of the smallest ones is an epoch.

According to the ICS, we’re currently  living in the Holocene epoch,   which began after the last major ice age. But some geologists have argued that humans  have made such a big impact on the earth,   that we’re currently living  in a new geological epoch. They call it the Anthropocene, from  the Greek words for “human” and “new.” So in 2024— after much debate— members of the ICS   took a vote on whether we’re  living in the Anthropocene.

And their decision was… not yet. Part of the issue is that, in order to  determine that we’re living in a new epoch,   there has to be a precise starting  point, and geologists would need   a physical representation of  it in the global rock record. Like, how a spike of iridium marks the point when  an asteroid killed all the non-avian dinosaurs.

But the ICS members couldn’t agree on what the  starting point would be for the Anthropocene. Some say that human influence revved  up with the invention of agriculture. Yeah, blame it on the Mesopotamians—  that’s what I always do.

Others say our impacts went into warp-speed during  the Industrial Revolution of the 18th century,   when Britain started going  steady with fossil fuels. “Blame it on the Brits”— that’s more like it. Still others proposed that the starting  point be— drumroll, please— the 1950s. Wait, blame it on… Boomers?

Nah, that’s too perfect. See, in the 1950s, nuclear weapons tests changed  the chemical composition of the atmosphere,   leaving a distinct radioactive  signature on all the sediment   that’s formed and on everything  that’s lived and died ever since. That means you literally can’t shake a stick  without touching evidence that humans were here.

To illustrate their point, the pro-Anthropocene  geologists looked to Crawford Lake, Ontario. Well, the sediment at the bottom of it. In its layers are radioactive  plutonium deposits that show   the exact moments of hydrogen bomb tests in 1952.

Personally, I would’ve picked  the ground beneath the first   pogo stick factory to convince  them, but, you know, whatever. But even with that evidence, the ICS  ultimately voted “no” on the Anthropocene. It was a controversial decision,  but they had their reasons.

For one, most epochs span  thousands or millions of years,   and it’s only been a few decades since the 1950s. Other geologists argued that the Anthropocene  doesn’t count as an epoch because we’ve been   changing the planet way before the 1950s,  just not at the same time everywhere. We didn’t start the Anthropocene!

It was always happening, it was never happening! But that doesn’t mean humans haven’t  had a major effect on the earth. Even the geologists who voted against  putting us on the deep-time calendar   say we’re still impacting the  planet in real and serious ways.

We don’t need to look to the  geologic record to understand that. The signs are everywhere. And if you asked our pal John what he thinks,  I’m pretty sure he’d be pro-Anthropocene.

So the real question is: can  we turn this thing around and   reverse the damage we’ve done to our planet? Dwayne, what are your thoughts? Hm, you’re right.

Those questions are above your paygrade. Wait, what are we paying you? The bad news?

Many experts say it’s impossible to completely   reverse the changes we’ve  made to the earth so far. No takesies-backsies on plastic rocks. The good news is: it could be possible  to set ourselves on a different path,   where we live within our planet’s  capacity instead of exploiting it.

Take dams, for example. We’ve built a lot of them for a lot of  reasons, including preventing floods. But by chasing a solution to one problem,  we’ve actually created whole other one.

Normally, a river forges natural meanders,  with sediment building up on either bank. And it carries sediment all the way to its delta. There, sediment provides nutrients to the   ecosystems and builds up rock as  protection from erosion and storms.

But dams can throw rivers all out of whack. When a dam gets built across a river,  its reservoir traps much of the water   washing downstream— and most of the  sediment the water carries, too. The water leaving the dam  contains hardly any sediment,   which actually increases the water’s  ability to erode the shoreline.

Meanwhile, the delta is left without  the nutrients and protections it needs. And sediment can build up so  much on the other side of the   dam that its reservoir can’t hold as much water. The quality of the river water changes,   potentially reducing the amount of dissolved  oxygen— something necessary for marine life.

So human-made structures like  dams can cause a lot of dam-age. Come on, more puns? This is serious!

But we might be able to reverse some  of that damage by removing them. For nearly a hundred years, a dam on the coast of   western Washington blocked the Elwha  River from emptying into the ocean. But since the dam was removed in 2011,  the unleashed sediment has already rebuilt   beaches, sandbars, and lagoons, restoring  habitats for diverse plants and animals.

Similar efforts are taking place across the world,   with floodwalls coming down and rock  rapids and wetlands building up. Unfortunately, though, we can’t fix  all our problems by making like an   HGTV show on demo day and letting  Mama Nature do all the remodeling. Wait, we can’t, right?

No, I’m being told that, uh,  that would be total chaos. We can’t do that. Some aspects of our planet won’t revert  back to their pre-humanity selves.

Human-caused climate change is already bringing  warmer, shorter winters; rising sea levels; and more frequent extreme weather events. But these challenges won’t be  felt in the same way everywhere. So, as warming increases, we’ll need all kinds  of different strategies for adaptation— or,   adjustment to climate change’s effects.

Take the Netherlands, for example. Most of the country lies either  below or just barely above sea level. They’ve had to do so much work to keep the  water in check that they have a saying:   “God made the earth, but the  Dutch made the Netherlands.” And as sea levels rise, flooding  isn’t a question of “if” but “when.” So, people in the Netherlands are working  together now to plan for those changes.

Instead of building higher and higher  floodwalls, they’ve relocated people’s   homes to safer places and given rivers wider  floodplains, so they have room to ebb and flow. They’ve also restored wetlands, which help  buffer shorelines from erosion and rising tides. And in Colombia, there are efforts to protect  rainforests where medicinal plants grow,   which many people rely on  to treat illnesses at home.

There’s also work happening to increase  the diversity of taro crops in Samoa,   so this food resource is more  resilient to droughts and cyclones. Geology is a huge part of  figuring out these solutions. Environmental geologists study the problems  that arise when human activities impact   geological processes, through things  like flooding, erosion, and pollution.

They’re key to planning for natural disasters,  repairing damage to rivers, making sure water is   safe to drink, and identifying spots for landfills  that are less likely to pollute groundwater. There are even geologists working  to slow down climate change. One strategy is capturing and  storing carbon dioxide in the ground,   instead of letting it waft into the  atmosphere and crank up the thermostat.

Geologists play an important role in   identifying places in the ground  where carbon can be locked away. They’re even developing new techniques, like  enhanced rock weathering, which removes carbon   dioxide by speeding up geological processes that  usually take hundreds or thousands of years. Pretty cool, right?

But that’s not to say these  strategies are a miracle cure. There are no shortcuts for getting  out of the current climate crisis;   we have to find pathways through it. Climate scientists and environmental  geologists agree: the most effective way   to lessen climate change is to limit  carbon emissions from fossil fuels.

You can learn more about that in  earlier an earlier episode of this   series and over on Crash Course Climate & Energy. So, is it the Anthropocene yet? Officially, no.

But there’s no doubt humans have transformed  the earth— and continue to do so today. A million years from now, if some future  society probes the rock record of right now,   they’ll find evidence of plastic  debris, mining, landfills, and dams. They’ll find remains from fewer wild  species, and more livestock and crops.

They’ll find traces of the fossil fuels we burned  and the radioactive signatures we left behind. But maybe they’ll also find  signs that we changed course   and learned to live within the planet’s capacity. In our final episode, we’ll explore  the geology of other planets and ask,   “Is there really no place like Earth?” See you then.

Thanks for watching this episode of  Crash Course Geology which was filmed   at our studio in Indianapolis, Indiana, and was  made with the help of all these nice anthros. If you want to help keep Crash  Course free for everyone,   forever, you can join our community on Patreon.