MARY LOUISE KELLY, HOST:

A team of archaeologists has announced a surprising discovery about our very early ancestors, Stone Age humans who were building with wood some half million years ago. As NPR's Gabriel Spitzer explains, it's thought to be the oldest known wooden structure in the world.

GABRIEL SPITZER, BYLINE: The Kalambo River snakes along the border between Zambia and Tanzania before plunging nearly 800 feet over Kalambo Falls. In 2019, up above the falls, Maggie Katongo and a crew of archaeologists were burrowing into the soggy banks.

MAGGIE KATONGO: Of course, as we went down and kept on digging, we found the water, and it kept on coming up. And we had to use buckets to kind of remove the water from the trenches.

SPITZER: Katongo is curator of archaeology at Livingstone Museum in Zambia. And that water they were baling was key to what they were looking for - ancient wood worked by early humans into tools and structures. Wood artifacts don't last like stone tools do. But after thousands of years under water and clay, fragments can survive. Larry Barham of the University of Liverpool was chief of the excavation. He says eventually they found more than just fragments.

LARRY BARHAM: When we first uncovered it, it didn't look particularly exciting. It's basically one log lying horizontally over another one. But then when you look closely and you remove the sand around it, you can see where the one sits on top of the other is a notch.

SPITZER: That notch and other parts of the logs showed telltale signs of being cut, chopped and shaped by human tools.

BARHAM: This thing was an intended component. It was, in a sense, engineered.

SPITZER: But engineered for what? Barham mulled over the question.

BARHAM: To interpret this, I drew on my childhood experience with a toy called Lincoln Logs. People laughed at me. They still do. Your listeners will all be familiar with Lincoln Logs and the notches which allow you to pile up and make a log cabin. And the Lincoln Logs really, really helped.

SPITZER: Barham concluded the wood formed part of a base or platform. If so, it's by far the oldest known example of people building with wood. The team dated it to about 476,000 years ago. That's well before modern humans evolved. Early hominins are thought to have been nomadic. This site suggests they could have had at least semi-permanent settlements. Maggie Katongo says that has experts rethinking their assumptions about Stone Age people.

KATONGO: When we make reference to these hominins, we always perceive them as primitive. But from the technology that we've been able to discover at the site, you'd see how sophisticated these hominins were.

SPITZER: The team's findings are published in the journal Nature.

Gabriel Spitzer, NPR News.