The landscape along the Buffels River in South Africa’s Namaqualand region is dotted with thousands of sandy mounds that occupy about 20% of the surface area. These heuweltjies, as the locals call them (the word means “little hills” in Afrikaans), are termite mounds, inhabited by an underground network of tunnels and nests of the southern harvester termite, Microhodotermes viator.

I’m part of a group of earth scientists who, in 2021, set out to study why the groundwater in the area, around 530km from Cape Town, is saline. The groundwater salinity seemed to be specifically related to the location of these heuweltjies. We used radiocarbon dating; dating the mounds, we reasoned, would allow us to see when minerals that were stored in the mounds were flushed to the groundwater.

The tests revealed far more than we expected: Namaqualand’s heuweltjies, it turns out, are the world’s oldest inhabited termite mounds. Some date as far back as between 34,000 and 13,000 years. The oldest previously known inhabited mounds were 4,000 years old (from a different termite species from Brazil) and 2,300 years old (from central Congo).

This is more than just an interesting scientific find or historical curiosity. It offers a window into what our planet looked like tens of thousands of years ago, providing a living archive of environmental conditions that shaped our world.