Earthworks spotted in the Amazon hint at huge ancient civilization

**Nick Patrick-Howe** (0:04)
Nature, I don't know yet.

**Sharni Bundel** (0:06)
Why is life so far?

**Benjamin Thompson** (0:08)
Like, it sounds so simple.

**Sharni Bundel** (0:09)
They had no idea.

**Jakob Winter** (0:10)
But now the data's...

**SPEAKER_5** (0:12)
I find this not only refreshing, but at some level astounding.

**Benjamin Thompson** (0:24)
Welcome back to The Nature Podcast. This week, the structures hidden beneath the Amazon's trees...

**Nick Patrick-Howe** (0:30)
And the earliest fossil squid ancestor. I'm Nick Patrick-Howe.

**Benjamin Thompson** (0:35)
And I'm Benjamin Thompson.
For 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.

**Martti Pärssinen** (1:17)
We gave the name Acre for this civilization, because at first we don't know what they call themselves. But this name come from the Acre River, which pass Riupranku, the capital of Acre state.

**Benjamin Thompson** (1:32)
This is Martti Pärssinen from the University of Helsinki in Finland, who's been studying this region and the Acre civilization for many years. The Acre 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 meters 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 two thousand years before the European conquest of the 1500s. And they're not just next to rivers and waterways, they're spread out. Now exactly what these structures were used for is unknown, but evidence points to them being important administrative and socio-cultural centres. This week, Martti 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.

**Martti Pärssinen** (2:36)
We were very surprised ourselves. When we made different kinds of calculation, we always conclude that we should have in total more or less from 24,000 to 30,000, so that it is a huge amount of earthworks.

**Benjamin Thompson** (2:56)
Many of the previously identified earthworks were found using aerial photography or satellite imagery, mostly in deforested areas. But that could only take the search so far.

**Martti Pärssinen** (3:08)
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 an airplane and a LIDAR system.

**Benjamin Thompson** (3:25)
LIDAR systems fire rapid pulses of laser light at a target 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. In fact, plane-based LIDAR systems have been used in the Amazon before to detect structures hidden beneath the trees.
This is what Marty and his colleagues did, conducting surveys in Acre and Amazon estates, totalling about four and a half thousand square kilometres. They found a bunch of previously unseen earthworks.

**Martti Pärssinen** (4:09)
We found in total about 430 earthworks, and four hundreds of these were new ones. Most of them were these geocliffs with geometric shapes and with ditsies, and we also found many roads.

**Benjamin Thompson** (4:27)
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. And the team put a range on when these newly identified structures might have been made.

**Martti Pärssinen** (4:43)
We have collected more than 160 radiocarbon samples. And it seems that the first geocliffs were built about 600 BC.
And they stopped to construct them about 850 AD.

**Benjamin Thompson** (5:00)
Not all of the structures the team found could be attributed to the aquary, and were likely built later. But the team combined the data they'd gained with previously collected information to make some inferences about the aquary civilisation.
By extrapolating out from what had been found, the team estimate the total size of the aquary civilisation to be over 180,000 square kilometres, over three times the size of Marti's previous estimates. And 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.