How long will traces of our civilisation last?

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1:07And I haven't found any one at all yet. Nothing.

1:12Caroline Steel:Hello and welcome to CrowdScience from the BBC World Service. And if we now look down here, actually geologically, all of these olivey green rocks are pieces of a material called pyrite, or fool's gold to give it its common name. But it's here mixed in with bolts and screws and hinges and undescribed bits of rusty metal. I'm Caroline Steele, and you're listening to fossil hunter Paul Davis, showing producer Sam the tricks of the trade. So actually, strangely enough, these patches with the rusty metal and the fool's gold are one of the best places to look for fossils. All right, I'm determined now to find something in here.

1:52Yeah, so this is the tree. And so what you do is you just look through and you're looking for that shape of ammonite. There is no guarantee, of course. This is called fossil hunting, not fossil finding.

2:05Caroline Steel:We're hunting for traces of species which once roamed our planet. thanks to listener Steve, who has two big questions for us. It all started with my daughter, who's just been taking a big set of exams, and one of her exams required her to study the famous poem Ozymandias. And in it, there's this passage, My name is Ozymandias, King of kings. Look at my works, ye mighty in despair. Nothing beside remains. Round the decay of that colossal wreck, boundless and bare, the lone and level sands stretch far away. And it reminded me of this unsettled feeling I've had for years and years, knowing that everything on Earth's surface disappears over geological time, and in quite a short period of geological time too.

2:55And that was a really, an easy feeling for me. And that's what prompted my questions.

3:00Caroline Steel:So what is your question for crowd science? If an intelligent animal had built a civilisation on Earth that lasted, say, for 50 ,000 years, which is way more than humans have ever managed, and they'd done that at some arbitrary point in the past, 372 million years ago, would we even know? Would there be any traces left today besides fossils? And the related question is, if we look forward 20 million years, 780 million years in the future, will there be anything left of us, of our civilization? That is, it's giving me a slightly unsettled feeling. it sort of both makes me feel like gosh what's the point in anything because yeah we're going to be completely untraceable in the future and then also gives me sort of a sense of urgency at the same time which is a stressful combination it's sort of like we're a matchstick burning in the face of the sun we're not nothing but we are so close to nothing compared to the whole of reality that it's really impossible to get your head around.

4:10Will any bit of our buildings be left? Will any of our artefacts last?

4:16Caroline Steel:Thanks for getting in touch, Steve. I think I know the place to start. He's not a paleontologist, but an astrophysicist. Steve's two questions, one which looks back and one which looks forward, are in fact the same question. How will the Earth's surface change over timescales that long, such that you'd be able to find evidence of something that happened in the distant past. This is Adam Frank from the University of Rochester in the US. He normally spends his days trying to figure out how to find life on other planets. But sometimes that leads him right back to Earth. I was interested in the idea that climate change may be a common thing that happens to any technological civilization.

5:05That basically, if you're harvesting a lot of energy from your planet, you should expect to trigger some version of climate change. And so I went to meet with Gavin Schmidt, who's the head of the Goddard Institute for Space Studies. And I went into his office and I said, I'm thinking about climate change on alien planets, because of course we know that there's been no other civilization on Earth. And he stopped at me and said, how do you know that? And my jaw just dropped down to the floor, because I thought I had the weirdest question ever. And now he had out-weirded me. And the thing was, it wasn't that Gavin thought there was a previous technological civilization on Earth.

5:43He was just doing the thing that is the most beautiful part of science. He was just asking a question and asking, how would you know the answer?

5:53Caroline Steel:Adam and Gavin landed at a very similar question to our listener Steve's. If there had been previous advanced life on planet Earth, how would we know? In this episode of CrowdScience, we're on the hunt for clues. Producer Sam is searching for actual fossils. They're cool-looking rocks, but I don't think those are any fossils. While we explore what evidence an ancient civilisation might have left behind, and what traces we might leave for the archaeologists of the far future. But Adam and Gavin are already one step ahead of us. Their curiosity led to something called the Silurian Hypothesis.

6:38Caroline Steel:Named after an ancient lizard-like species from the BBC science fiction show Doctor Who, the Silurian Hypothesis proposes that if there was a technologically advanced civilisation hundreds of millions of years ago, we wouldn't be able to find traces of it. Everybody always thinks like, oh, fossils. Well, of course stuff will be fossilized. But the problem with fossils is that most things are not fossilized. It's only a tiny fraction of Earth's life that has ever become fossilized, especially if your civilization only lasts a brief time geologically. So imagine that you have a 10 ,000 year long civilization, which is a blink of the eye for geology.

7:22that's too short to really create a lot of fossils. So in general, the whole argument comes down to it's unlikely that anything from a technological civilization could survive that kind of duration of time.

7:36Caroline Steel:OK, so we definitely need to have a look at fossils. How likely is it that we would find fossils from a previous technological species if one had existed? And in the future, will we humans leave enough for archaeologists to find? Going forwards, what will we leave? We probably will have changed the rock strata. So if you go to the Grand Canyon, you'll see layer after layer of rock going down. And that's a record going back hundreds of millions of years. And the material, the actual chemical composition of those layers is actually telling you what physical processes were happening at the time. So clearly, we already see this, that the rising of the temperatures because of human-made climate change, changes in the ocean levels, all of these things are going to change what gets deposited in the rock.

8:27And that you would be able to see probably hundreds of millions of years from now. You'd see that there was a difference in the oxygen isotopes, the carbon isotopes, due to the fact that the Earth's climate system had changed due to human activity.

8:42Caroline Steel:It's interesting because in some ways it's such a sort of important and fundamental question, but then also at the same time, how on earth do we work it out? Because, you know, we're only alive for 80 years if we're lucky and we're trying to predict how long the traces of our civilization will last and we just can't do those experiments. We can't do the experiment in the sense of running, we can't watch what's going to happen to our civilization. But the beautiful thing about science, there's ways of answering the question. You can look at what we call proxies. We can look at other things and how they erode over time.

9:19Look at the geological history.

9:21Caroline Steel:I'm sure you're very busy, but I don't suppose you have time to do all that work and let us know. Yeah, hopefully, that's probably not work I'm going to do, but because my main job is to look for life in the universe on other planets. But hopefully someone else picks up on it. Okay, adding strata or layers of rock to the list of things we need to investigate alongside fossils. Luckily, I'm joined by producer Sam, who we heard digging for fossils at the start of the show. Sam, Adam said it's really hard to become a fossil, which surprises me. Yeah, unfortunately, your chances of becoming a fossil are extremely low, actually.

9:59Caroline Steel:It's estimated that it's as low as less than one-tenth of one percent of all species that have ever lived become fossils. So there'll be loads of species that exist that we don't even know about and never will know about. Yeah, your chances of becoming a fossil are pretty low. And then, of course, on top of that, you have even lower chances of being found by someone. So that all sort of backs up what Adam said, right? Even if a previous technological society did exist, maybe we would never find it. Yeah, but I mean, there are still fossils, so it's not completely impossible. And there are a couple of spots around the world where there's actually lots and lots of fossils.

10:39Caroline Steel:I got to go to one of them in the UK recently, Lime Regis on the Jurassic Coast. And I went to the beach there with geology curator Paul Davis from the local museum, who gave me the lowdown on fossils and how they're made. So fossils go through a process of a change from a living creature to, in essence, stone. And that can be a chemical change of the shell, or in some cases, they don't even change the chemistry of the shell. We still have the original shell of the animal, or it can be a bone, and the bone can slowly change. It's called a process of per-mineralization, where the chemistry of the bones or the shells are slowly changed through millions of years of water and chemicals and minerals flowing through the sediments and rocks that they're embedded in.

11:33Caroline Steel:So let's say I would like to be a fossil for the future. Are there any things I can do to optimize my chances? Well, you're doing not too bad for a start. You've got hard parts, you've got bones, you've got teeth. Your best chance is to be buried at sea. Make sure that you get laid down somewhere in a nice sedimentary basin where it's laying down very fine-grained sediments and it's deep enough water so the bottom waters of where you're being laid down aren't very rich in oxygen. but the chances of humans becoming fossils will be patchy, as is most life throughout geological time. We as paleontologists are trying to recreate past lives with tiny little snapshots on windows of life.

12:23Caroline Steel:OK, so remind me to get buried in the deep ocean, which hopefully I have a while to organise. Sam, if it's easiest to become a fossil at the bottom of the sea, not to question your methods but why are you looking on a beach good point i did ask paul why this spot is so fossil rich lime regis and the jurassic coast in particular are incredibly good for finding fossils because most of the rocks here were laid down at the bottom of an ocean and the seas that were there in the jurassic were teeming with marine life from small little things like ammonites up to fish to the more famous marine reptiles called ichthyosaurs and plesiosaurs and of course the more life the more chance those will get preserved as fossils and the reason we find such a lot here it's a happy accident of geography and the geology we're here on a eroding coastline which means that fossils are constantly being washed out of these rocks onto the beach for people to find.

13:27And it was just also a coincidence that the sorts of rocks that preserved here were absolutely perfect for preserving fossils.

13:36Caroline Steel:So Sam, talk me through what you're actually doing. How were you looking for these fossils? I'm sort of picturing that there are so many that you just sort of spot them, walk over to them and pick them up. Well, not quite. It wasn't that easy. We did have to really look. But Paul did give me a couple of really helpful tips. You are looking for small, regular and symmetrical. They tend to be various shades of greys and browns. And I always say what you want to do is look with your eyes and your fingers. You do not need to hammer for everything that you see in front of you. OK, I have my fingers crossed for a fossil.

14:16Caroline Steel:At this point, did you think you stood much of a chance? Yeah, I actually did. because when I was coming into town on the bus, I noticed that on every shop door and even on the lamppost there, they had images of ammonites, these iconic spiral shells. And I just felt like with all of this imagery, there must be loads and loads of them on the beach. Okay, well, we'll check back in with you later to see if you had any luck. It seems that we can't rely on fossilised remains to tell us everything about ancient species. So maybe there could have been a former technological civilization in Earth's distant past.

14:53Caroline Steel:That's what we're looking in. Pop quiz. What's in your kid's lunchbox? At Whole Foods Market, they've already done the studying. Over 300 food ingredients are banned from their shelves. No hydronated fats in the peanut butter and no high fructose corn syrup in the cookies. And for sandwiches, there are no synthetic nitrates or nitrites in any of their deli meat. so you can pack lunch boxes with peace of mind. Get back to school ready at Whole Foods Market. Apple Vacations, where your story starts. The Summer Savings Event is here at Apple Vacations. It's the perfect time to bring everyone together for the getaway you've been dreaming about.

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15:48Caroline Steel:Apple Vacations, where your story starts. To next.

15:59Caroline Steel:You're listening to CrowdScience from the BBC World Service, the show that searches for traces of answers to your science questions. I'm Caroline Steele, and in this episode, we're answering two questions from listener Steve. Far in the future, will there be anything left of us humans? How long will our remains remain? And could there have been another technological species on Earth before humans? In all honesty, as a paleontologist and a geologist, I just don't think that's possible. I think it's a lovely idea, but I think we will leave a trace. Here are two scientists who wrote a book called Discarded, how technofossils will be our ultimate legacy.

16:42Caroline Steel:as a sort of answer to the Silurian hypothesis. I am Professor Sarah Gabbett from the University of Leicester and I am a paleontologist. I'm Jan Zelishevich. I'm a geologist and paleontologist and emeritus professor at the University of Leicester. They don't necessarily think it would be fossilised bodies that would give away ancient advanced species, but instead fossilised traces of their technology. Geologists and paleontologists look through the strata of the entire Earth's history from four and a half billion years ago, minutely. And we can say with great assurity, actually, that no traces of some technological civilization have been found previously.

17:29That's either with the record of stuff, you know, so materials or objects, But also we can look at the chemical signals through time and we can tell from those as well that there's never been a time like there is today.

17:47Caroline Steel:But it just it feels like humans have been alive for such a small fraction of the Earth's history, right? Like could there not have been another sort of blip ages ago that sort of been lost to huge geological time? There might have been intelligent dinosaurs or super philosophical ammonites, but not manipulative ones, not ones that made lots of things and changed the earth in the way that we did. Because had they done so, they would have left a big mark in the geological record, and we'd have found it. Of things that have left a mark in the geological record and were just a blip, we have the example of the big meteorite that killed off the dinosaurs.

18:32That was a very short blip, but it had a very big effect, and we found that, in this case, we are the meteorite.

18:38Caroline Steel:We might not be a giant ball of rock colliding with Earth and wiping out species, but we are interfering with them in other surprising ways. All of the animals and plants that we've either made extinct or transported around the Earth to reshape Earth's biology, We've altered the path of biological evolution. Therefore, we've altered the pattern of the fossil record. And that's going to show up first. And using that as a guide, our far future explorers are going to wonder what happened. Why did that happen? And they're going to hone in on the layer where all this began. And that's the layer of us.

19:21Caroline Steel:We humans have had a huge impact on other animals. If we're not transporting them from one corner of the earth to another, we're picking winners and losers. These days, only 4 % of mammals are wild mammals. The other 96 % are either us or the animals that we farm to eat. So we've completely changed the diversity of life. Look at chickens. We kill 75 billion chickens every single year. So that goes to show that we're making lots and lots of this strange animal. And chickens are two thirds of the biomass of bird life on Earth. Two thirds of it is chickens. Wow. So future paleontologists are going to be like, why are there all these birds and why do they all look the same?

20:19Caroline Steel:And why are they dying on mass? Yeah, exactly. Another thing future paleontologists might notice is how we're creating deadly waste that we have to bury deep underground. Yeah, nuclear waste, it's a good example actually of kind of one of the only things that we've really thought about deeply, about how long it's going to last, is nuclear waste. And, you know, we're still kicking that ball down the park, really. And then there are the other methods humans use to generate energy. Things like giant coal mines, massive dams and also less direct traces. One signal that we have already left behind from the burning of huge amounts of coal and oil and gas is fly ash.

21:03That's gone up into the atmosphere as smoke and as pollution. What are called spherical carbonaceous particles. They're very tiny bits of unburnt carbon. They're really, really robust. They're indigestible and they will simply stay there as a layer within strata. Far future paleontologists will be able to find those little bits of fossil carbon-rich fly ash in much the same way that we now routinely find fossil spores and pollen in strata. You take a bit of the rock, you dissolve it up, look at the remains under a microscope and hey presto, there will be these quite unique bits of fly ash. There's nothing quite like it in the geological record.

21:46Caroline Steel:So the chemical traces in rocks will give us a way to future paleontologists. But what about more concrete clues? So let's say, for instance, if you have a city like Venice or New Orleans or Shanghai, if you're sinking, eventually it's going to begin to be covered by layers of sand and mud. And so those crumbling buildings, they're going to be in pretty poor shape. So it's going to be a rubble layer. But beneath that, let's say the underground car parks and sewage systems and all of that, they're going to be much better preserved simply because they'll have a layer of soil and sediment and mud and sand on top of them and they will become strata.