Tens of Thousands of Earthworks Under the Amazon, and a Civilization of Perhaps Three Million
Using LiDAR to see through the rainforest canopy, archaeologists have found tens of thousands of earthworks in the southwestern Amazon, spread across more than 180,000 square kilometres, with a peak population that may have reached 3 million.
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There is an order of magnitude more earthwork buried under the Amazon than anyone guessed
Marti Pärssinen's team used airborne LiDAR to survey roughly 4,500 square kilometres of Acre and Amazonas states, and found around 430 earthworks beneath dense canopy, more than 40 of them never seen before. Extrapolating from that plus earlier data, the team estimates the region holds 24,000 to 30,000 earthworks in total — an order of magnitude more than the 2,000-3,000 Marti himself had previously guessed. Most of the earthworks are geometric geoglyphs and roads, built between roughly 600 BC and AD 850.
— Marti PärssinenSatellites only see the cleared land; only lasers see beneath the forest
The earthworks went undetected for so long because more than half of Acre state and most of Amazonas state are still forest-covered, and satellite imagery can only show the deforested areas. A LiDAR system fires rapid laser pulses at the ground; some of the beams slip through gaps in the canopy, reach the ground and reflect back, which builds a three-dimensional map of the terrain under the trees. Within the area mapped on these flights, the team found not only earthworks hidden by trees but also grassland structures that satellite images had missed — probably because the grass was too dense for them to show at the surface.
Pre-colonial Amazonia was not wilderness, it was home to three million people
Extrapolating from the new findings, the team puts the total area of the Ari civilization at more than 180,000 square kilometres, over three times previous estimates. Working back from the labour needed to maintain the earthworks, the local population at its height in AD 100-300 may have been between 1.25 million and 3 million. Marti concedes that these extrapolations are contested, and says a genuinely accurate answer would need more LiDAR flights, which are expensive; he believes the real number is about ten times more than he had previously imagined. This unsettles the old narrative that pre-colonial Amazonia was wilderness — humans had already urbanised there and altered the soils and the biodiversity.
— Marti PärssinenClothing that heals itself will also rot in the ground
Chinese researchers grew the mycelium of the Cordyceps militaris fungus into a dense network, then chemically treated it to make it flexible, and were also able to dye it in natural pale blues, reds, oranges and purples by adding pigment-producing yeasts. This living textile is self-cleaning, and when torn it will grow back together with nothing more than added nutrients and fresh mycelium. Discarded samples decomposed in soil in 41 days. But biodegradability brings its own trouble: under heat and humidity the material stretches and deforms easily, which is the main obstacle to commercialising it for clothing and packaging.
Small bubbles are louder than big ones, and the sound reveals their size
French physicists wanted to work out what determines how loud a bubble is when it enters water. They made bubbles two ways: squirted directly out of an underwater nozzle, or formed when a droplet hits the water surface and makes a crater that closes and traps a bubble. The results showed that the small bubbles from the droplet method were often louder than the larger bubbles the nozzle produced; and a given bubble is also louder when contracting than when growing. The work could be used to infer bubble size and state from sound, with potential uses including monitoring underwater gas leaks.
Cephalopods learned to adjust buoyancy and leave the seafloor almost as soon as they appeared
Palaeontologists have reported a set of small fossils roughly 515 million to 521 million years old, with shells about 4.5 millimetres long, internally divided into chambers, and preserving the soft-tissue siphuncle — the structure modern cephalopods use to pump gas in and water out of the chambers to control buoyancy. The oldest cephalopod fossils previously known were around 490-495 million years old, while cephalopods split from the other molluscan branches around 525-535 million years ago, leaving a gap of twenty to thirty million years. These new fossils fill that gap, showing that soon after cephalopods appeared they evolved chambered shells with adjustable buoyancy, which let 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 | around 430 (more than 40 of them new) | 0:45 |
| Period the earthworks were built | roughly 600 BC – AD 850 | 0:45 |
| Time for the fungal textile to decompose in soil | 41 days | 8:37 |
| Length of the cephalopod fossils | about 4.5 millimetres | 18:07 |
| How much older than the oldest known cephalopod | about 20 million–25 million years | 18:07 |
Glossary
- LiDAR
- A technology that measures distance with laser pulses to generate three-dimensional images of the ground surface, and can penetrate the forest canopy.
- geoglyph
- A geometric shape built at large scale on the land surface, common in ancient earthworks.
- siphuncle
- A soft-tissue tube inside a cephalopod shell connecting the chambers, used to regulate buoyancy.
How to listen
Archaeology enthusiasts and environmental professionals who follow pre-Columbian Amazonia, and also biology students interested in cephalopod evolution.
The research highlights in the last two segments can be skipped according to interest without losing the Amazon thread.