Earthworks spotted in the Amazon hint at huge ancient civilization

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1:37Welcome back to The Nature Podcast. This week, the structures hidden beneath the Amazon's trees and the earliest fossil squid ancestor. I'm Nick Pertridge-Hale and I'm Benjamin Thompson.

1:59For our first story this week, we're heading over to the southwest corner of the Amazon to hear about the discovery of a lot of ancient human activity that's long been hidden from view. Specifically, we're heading to an area in what is now the Brazilian states of Acre and Amazonas, close to where the borders of Brazil, Peru and Bolivia meet. Between around 700 BC to 900 AD, this area was home to people who researchers are now calling the Acre. We gave the name Akkuri for this civilization because at first we don't know what they called themselves. But this name comes from the Akkuri River, which passed Ryupranku, the capital of Akkuri state.

2:46This is Marti Parsinen from the University of Helsinki in Finland, who's been studying this region and the Akkuri civilization for many years. The Acheri were prolific builders, and previous work has uncovered over a thousand earthworks, large structures comprising of mounds and troughs of dirt that can be several metres tall or deep. These often form roads and geoglyphs, giant geometric shapes, often many hectares in size. Some of these ancient earthworks are estimated to date back perhaps 2 ,000 years before the European conquest of the 1500s. And they're not just next to rivers and waterways, they're spread out.

3:29Now exactly what these structures were used for is unknown, but evidence points to them being important administrative and socio-cultural centres. This week, Marti and his colleagues have uncovered many more previously hidden structures, and they've used this information to estimate how many there might be in the area. And it's a big number. We were very surprised ourselves. When we made different kind of calculation, we always concluded that we should have in total more or less from 24 ,000 to 30 ,000, so that it is a huge amount of earthworks. Many of the previously identified earthworks were found using aerial photography or satellite imagery, mostly in deforested areas.

4:18But that could only take the search so far. Because still more than half of the Acre and most of the Amazonas is under the forest. And that's why we couldn't continue the work by this way. And then we started to negotiate the possibility to get airplane and LIDAR system. LIDAR systems fire rapid pulses of laser light to targets and measure how long they take to bounce back, enabling the system to build up a 3D map of the object being looked at. In the forest, some of the lasers find gaps in the canopy and reach the ground before bouncing back, allowing a topographic picture beneath the forest to be built up.

5:02In fact, plane-based LiDAR systems have been used in the Amazon before to detect structures hidden beneath the trees. This is what Marti and his colleagues did, conducting surveys in Acre and Amazon estates, totaling about 4 ,500 square kilometres. They found a bunch of previously unseen earthworks. We found in total about 430 earthworks, and 400 of these were new ones. Most of them were these geocleaves with geometric shapes and with litsies, And we also found many roads. And while the team found a lot of earthworks covered by trees, they also found a lot in clearings that had been missed in satellite imagery, perhaps because they were too covered up with grass.

5:51And the team put a range on when these newly identified structures might have been made. We have collected more than 160 radiocarbon samples, and it seems that the first geoclifts were built about 600 BC and they stopped to construct them about 850 AD. Not all of the structures the team found could be attributed to the Aquari and were likely built later. But the team combined the data they'd gained with previously collected information to make some inferences about the Aquari's civilisation. By extrapolating out from what had been found, the team estimate the total size of the Aquari civilization to be over 180 ,000 square kilometers, over three times the size of Marti's previous estimates.

6:41And by looking at areas where earthworks were present in high or low density, they put a number on how many earthworks were potentially present in this expanded area. We estimated between 24 ,000 and 30 ,000 earthworks in total. And we made a different kind of calculation by using different evidences, but we conclude the same results. And this changed also our own idea, because I estimated maybe 2 ,000, 3 ,000 in total, but it's 10 times more than I expected before the LiDAR campaign. To put this into context, these sorts of numbers have been put forward as potentially the total amount of earthwork seen in the whole of the Amazon basin.

7:31The area that Marti and his colleagues have been looking at is only about 3 % of that. This means that potentially the whole Amazonia may have tens of millions. But of course we don't know, but at least this obligated us to study it more. The team estimate that at the Aquari civilization's peak, which they put at around 100 to 300 AD, the population in the area could have been between 1.25 and 3 million people, based on their calculations of how many folk would have been needed to build and maintain the earthworks. But, of course, many of these results are, in part, extrapolations. And there will be questions about whether the small area the team surveyed using LiDAR is representative of the larger region.

8:19Marti acknowledges this, but is confident in the team's calculations. However, he concedes there is one way to get an accurate picture of what's going on. Of course, in future, hopefully, we have more possibilities to make new LiDAR campaigns to have more actual information. But the thing is that it is very expensive. The area is big, huge, and even now I think that our flights in archaeological research, it was about 10 times larger than earlier ones. What the team discover, and whether it confirms or alters their estimates, will have to wait for a future podcast. But this work, and other studies looking at other cultures in and around the Amazon, shows that the idea that this region was a sparsely populated wilderness in pre-colonial times is well out of date.

9:16Evidence points instead to the Amazon having areas of urbanisation and large populations populated by communities and cultures who shape the land, echoes of which can be found today in things like the location of Brazil nut trees, which evidence suggests were domesticated and cultivated for food. Our understanding of the pristine tropical forest, it is no more valid because so much has happened there and the humans have affected the biodiversity and also the soil composition and so on. We have started, I think, now a new era to understand more about the reality of Amazonia. And we need a lot of new studies to understand much better what was the impact of these past societies and civilisation there.

10:13That was Marti Parsinen from the University of Helsinki. For more on that story, check out the show notes for some links. Coming up, a fossil that may reveal how the ancestor of squids and octopuses evolved. Right now, though, it's time for the Research Highlights with Shownie Bundel.

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11:24A small sample was found to break down in soil in 41 days. But the same properties that make it biodegradable also make it susceptible to stretching, especially at high temperatures and humidity levels. Struck down the catwalk to science advances for more on that.

11:45Let's take a moment to listen to the relaxing sound of bubbles

11:54Relaxing unless you're an acoustic physicist with a special interest in bubbles that is Researchers in France were disturbed from their relaxation by a question What determines the volume of the sound each bubble makes as it forms underwater? Science could already explain the production of specific pitches, but the loudness was a mystery. So the researchers started blowing bubbles. They either used an underwater nozzle or released droplets onto a pool of water, creating a dimple that closed to then encase a bubble. Using a high-speed camera and an underwater microphone, they found that the smaller bubbles created by the dropping technique tended to produce a louder sound as they formed, compared to those produced by the nozzle.

12:37The sound was also louder when a bubble was actively shrinking rather than growing. The findings, the team says, could help researchers deduce information about bubbles from their sound alone, perhaps helpful for things like gas leaks. Float along to that research in physical review fluids.

13:05Paleontologists have discovered the oldest example of a cephalopod, or kephlopod. This is the group of soft-bodied marine animals that include squids, octopuses and nautiluses. They're thought to have evolved during the Cambrian Explosion, a vast diversification of life that happened around 560 to 520 million years ago. But fossil evidence from that long ago has been hard to come by. There's been a few possibilities that paleontologists have presented, but nothing unequivocal. This new find may change that. In Nature this week, the authors describe a group of tiny fossils which have evidence of a structure known as a cyfuncle.

13:48This is a strand of tissue that passes through gas or fluid-filled chambers in cephalopods and helps them regulate their buoyancy, something that modern cephalopods have taken great advantage of, being hypermobile predators under the sea, and is therefore a key sign of these fossils being very early cephalopods. I spoke with Jakob Winter, one of the researchers behind the new work, who told me a bit more about cephalopod evolution. So cephalopods is something that we actually have a pretty good understanding of in terms of their evolutionary history because they produce a lot of beautiful fossils.

14:26Now, most living cephalopods are things like octopus and squid. The thing is that octopus and squid is actually a relatively recent invention. They evolved in a way where the shell that used to be on the outside moved inside the body. We have one living group of cephalopods called nautilus that still have this external shell. And when we look inside the shell, we can see that there are these chambers that the animal can fill in with gas, and that sort of allows them to regulate the buoyancy in the water column. And that's actually how the ancestors of squid and octopus also look like. So we can trace living octopus and squid back to a common ancestor with nautilus that had an external shell with these chambers.

15:11And then a very important feature is that inside that chambered shell, there is a soft tissue structure that extends all the way from the last sort of chamber that is open at the end of this shell where the animal sits. And then all the way in through to all the other chambers, which is the way in which the animal can sort of empty these chambers of water and fill them with gas. But if we go further back in time, we can trace back cephalopod ancestors to things that had sort of straight conical shells that still have these chambers and has got this sort of soft tissue tube called the psifungal, all the way back to the latest Cambrian around 490 to 495 million years ago.

15:51But before that 495 million years, there's been a bit of a gap, right? That's the thing. We have this gap where we know that keflopods must have existed going back to about 525, 535 million years ago. We know that that's when keflopods must have branched off from other mollusks. But we had no fossils that we convincingly could say was related to keflopods in this sort of 20, 30 million year interval. And now we have a fossil that helped us plug that gap. And so our audience won't be able to see the picture of your fossil. So could you maybe paint me a word picture of what it looks like? So the way the fossils look like is that you have these little conical shells.

16:33They're about four and a half millimeters long and they're preserved in different ways where we can see either the sort of external shell morphology. Some of them have been slightly abraded so we can see inside. And then we can see that there are little layers that are sort of regularly deposited inside the shell that give it sort of a chamfered appearance. Then we have some other fossils where the shell is not preserved, but instead we have preservation of the chamber that the animal lived inside, and then a soft tissue structure that extended down through the chambers, which is what we call the cyfungal.

17:07so by having these different modes of preservation that is overlapping between the fossils we can sort of piece it all together to understand how this animal looked like and so you mentioned that the earliest known before this cephalopod fossils were about 490 million years old how old is this one so it's a little bit poorly constrained but they are from a time period that is constrained to be about 515 to 521 million years old. So it's sort of somewhere in that ballpark that these fossils are. So that means that they are about sort of 20 to 25 million years older than the oldest known cephalopods that we had before that.

17:50How certain are you that this is in fact a cephalopod? Because I know there's been some other candidates that people weren't so sure about. So How sure are you that this one is truly a cephalopod? Well, I think the best way of putting it is that it's the best answer. It has got a surprising number of features that enable us to argue that it's not something else. There are other things, other groups of organisms that have sort of shells and that have potentially sort of deposits or layers inside their shell, but they look very different. So the combination of features that we see make it very compellingly a cephalopod other than other things.

18:29But of course, with evolution, there are obviously the chance that some things, they just end up evolving to look quite similar to each other. But the sort of burden of proof at the moment would definitely argue that these things are cephalopods rather than something else. What do you think this fossil tells us about cephalopod evolution? Now, one of the things is that the way that things look like when they first branch off isn't necessarily going to look perfectly like what they look like today. So one of the things that I probably envisioned was that the earliest keflopods may have looked not much like a keflopod.

19:06They may have looked something like a limpid, which is sort of what all these different molestate looked like early on. They were just sort of little slug-like things with a little sort of shell on their back. and then later in time they evolved this shell with chambers inside so they could start floating in the water column but so what we have now discovered is that they actually evolved that shell that they could use for floating almost as soon as they branched off from the other mollusks which is quite exciting and do you think that gave them any sort of advantage well the thing is that other mollusks they are sort of tied to be living on the seafloor either sort of moving around with their foot, sort of like a slug or a snail they do.

19:47And then we have other groups like bivalves, which have evolved to sort of being closed within the shell, and either they sort of borrow around in the mud or they sort of recline on the seabed. But kevalopods, by evolving a shell with chambers inside that they could fill with gas, that allowed them to lift themselves off the seafloor and float around in the water column, and that allowed them to explore other food sources. and at least later on that meant that they became carnivorous predators. Indeed they're very successful at that. And do you think there are any sort of broader implications from what you've found beyond the sort of cephalopod evolution?

20:24Well I think it might be a little bit premature to appreciate what the broader implications are of this in terms of what it means for the sort of ecosystem and evolution because we can't really say much about what these cephalopods they were capable of doing other than floating around in the water column Had they already become carnivorous predators, which would be really, really important for how they affected the whole ecosystem? Or had they just evolved to float around in the water column to feed on small plankton or whatever? These shells are obviously really, really small. That could be a bias given how these things have been preserved.

20:58So they could potentially have been bigger. Or maybe they genuinely were that small. And that meant that they wouldn't have been that important in terms of the role that they played in the ecosystem. I think what is most important is that it helps us to understand and fill this gap that there were in terms of when cephalopods evolved and how they evolved. That was Jakob Vinter from the University of Bristol here in the UK. For more on early cephalopods, check out the show notes for some links. And that's all for this time. If you'd like to stay in touch with us, you can. We're on email, podcast at nature.com, or you can find us on social media, at naturepodcast.

21:35I'm Benjamin Thompson And I'm Nick Parcher-Chow Thanks for listening

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