Scientists have long been baffled by the true origins of several strange-looking and densely packed mounds found across large areas in South America.
Now, a new study suggests a plausible explanation for how these mounds were formed.
Apparently, these regularly spaced mounds, which are also known as surales, are ejected by the guts of earthworms. In other words, they're earthworm poop.
How Surales Were Formed
In order to figure out how the surales formed, a team led by archaeologist José Iriarte of University of Exeter analyzed the chemical and physical makeup of the mounds.
They applied remote sensing techniques, and used satellite images and aerial photographs captured by a drone to study the landscape.
The surales, which were located throughout the Orinoco Llanos wetlands of Venezuela and Columbia, differ in size. The most massive mound can measure up to 196 inches (5 meters) in diameter and up to 78 inches (2 meters) in height, researchers said.
Up to 50 percent of the soil mass of the mounds were composed of earthworm casts or the muddy soil ejected from worm guts.
It was no surprise that earthworms left their casts behind, but how did the piles of poop become so massive?
Iriarte and his colleagues found that the surales are formed when big earthworms feed in shallow, flooded soils in the wetlands. As these creatures leave their larger wastes behind, the poop gets piled up into mini towers that begin sticking above the water's surface.
Over time, the pile of poop becomes large enough to form a mound. The largest ones are often created when the smaller ones are close enough to fuse together.
Implications Of The Findings
The new study has helped scientists solve the long-standing mystery of how these mounds were formed. Past studies have suggested that the mounds were formed due to termite activity or land erosion, but experts can now dismiss those theories.
Iriarte said the findings of the study helps scientists map and comprehend how massive landscapes such as mounds were formed. He said it will change how they think about human-built landscapes and naturally formed landscapes in South America.
The study is published in the journal PLOS ONE.