Tens of thousands of earthworks lie under the Amazon; the ancient civilization may have held three million people
Using LiDAR to see through the rainforest, archaeologists found tens of thousands of earthworks in the southwestern Amazon, spanning more than 180,000 square kilometers, with a peak population that may have reached 3 million.
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The earthworks buried under the Amazon outnumber guesses by an order of magnitude
Marti Pärssinen's team used airborne LiDAR to scan about 4,500 square kilometers in the states of Acre and Amazonas, finding roughly 430 earthworks beneath the dense canopy, more than 40 of them never seen before. Extrapolating from earlier data, the team estimates 24,000 to 30,000 earthworks in the region — an order of magnitude more than the 2,000-3,000 Marti himself had previously guessed. The earthworks are mostly geometric geoglyphs and roads, built between about 600 BC and AD 850.
— Marti PärssinenSatellites see only cleared land; lasers see under the forest
The earthworks went undiscovered for so long because more than half of Acre and most of Amazonas are still forested, and satellite imagery can only see cleared areas. LiDAR systems fire rapid laser pulses at the ground; some beams pass through gaps in the canopy and reflect off the ground, building a three-dimensional map of the terrain beneath the trees. In the area flown and mapped, the team found not only earthworks hidden by trees but also grassy structures that satellite images had missed — possibly because the grass was too dense to show at the surface.
The pre-colonial Amazon was not wilderness but home to three million people
Extrapolating from the new finds, the team puts the total area of the Ari civilization at more than 180,000 square kilometers, more than three times the previous estimate. Judging by the labor needed to maintain the earthworks, the local population during its peak between AD 100 and 300 may have been between 1.25 million and 3 million. Marti acknowledges the extrapolations are contested and says a truly accurate answer would need more LiDAR surveys, which are expensive; he believes the real number is about ten times what he had previously imagined. This unsettles the old narrative that the pre-colonial Amazon was wilderness — humans had long since urbanized here and changed the soil and biodiversity.
— Marti PärssinenClothes that heal themselves also rot in the soil
Chinese researchers grew the mycelium of Cordyceps militaris fungus into a dense network, treated it chemically to give it flexibility, and dyed it pale blue, red, orange, purple and other natural colors by adding pigment-producing yeast. This living fabric self-cleans, and a tear can be healed simply by adding nutrients and fresh mycelium. Discarded samples decomposed in soil in 41 days. But biodegradability brings trouble too: under high heat and humidity it tends to stretch and deform, the main obstacle to commercializing it for clothing and packaging.
Small bubbles are louder than big ones, and sound can reveal their size
French physicists wanted to pin down what determines the volume of a bubble entering water. They made bubbles two ways: shot directly from an underwater nozzle, or by letting a droplet hit the water surface to form a crater whose collapse traps a bubble. The results show that the small bubbles formed by the droplet method are often louder than the large bubbles produced by the nozzle; the same bubble is also louder as it contracts than as it grows. The research can use sound to infer a bubble's size and state, with potential uses including monitoring underwater gas leaks.
Cephalopods learned to adjust buoyancy and leave the seafloor almost as soon as they appeared
Paleontologists report a set of small fossils about 515 million to 521 million years old, with shells about 4.5 millimeters long, divided internal chambers, and preserved soft tissue — the siphuncle, which modern cephalopods use to fill the chambers with gas and expel water to control buoyancy. The oldest previously known cephalopod fossils are about 490-495 million years old, while cephalopods split from other mollusks about 525-535 million years ago, leaving a gap of 20-30 million years. The new fossils fill that gap, showing that soon after cephalopods appeared they evolved a chambered shell with adjustable buoyancy, letting them leave the seafloor and later become agile predators.
— Yaov ViIn their own words · checked verbatim
We were very surprised ourselves when we made different kind of calculation We always conclude that we should have in total more or less from 24 to 30000, so that it is huge amount.
Marti Pärssinen0:45
we found in total, about 430 earthworks, and 40s of these were new ones.
Marti Pärssinen0:45
Our understanding of the pristine tropical forests.It is no more valid because pema has happened there and the humans have affected the biodiversity and also the the soil composition and so on
Marti Pärssinen0:45
A 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.
The findings the team says, could help researchers deduce information about bubbles from their sound alone, perhaps helpful for things like gas leaks.
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 knownpos that we had before that
Yaov Vi18:07
Figures
| Earthworks newly found by LiDAR | about 430 (more than 40 of them new) | 0:45 |
| Earthwork construction period | about 600 BC–AD 850 | 0:45 |
| Soil decomposition time of the fungal fabric | 41 days | 8:37 |
| Length of the cephalopod fossils | about 4.5 millimeters | 18:07 |
| How much older than the oldest known cephalopods | about 20 million–25 million years | 18:07 |
Glossary
- LiDAR
- A technology that uses laser pulses to measure distance and build three-dimensional images of the ground surface, able to penetrate tree canopy.
- geoglyph
- A large geometric shape constructed on the ground surface, common in ancient earthworks.
- siphuncle
- A soft-tissue tube in the cephalopod shell connecting the chambers, used to regulate buoyancy.
How to listen
Archaeology enthusiasts and conservation workers focused on Amazonian prehistory, and biology students interested in cephalopod evolution.
The research highlights in the last two segments can be skipped by interest without affecting the Amazon main thread.