Archeologists have gotten increasingly better at reading the dirt. Over time, they’ve learned to pull more and more data from smaller and smaller samples of Earth.

A technique called microstratigraphy pushes that concept to the limit. It allows archeologists to detect miniscule traces of human and animal presence that conventional excavation techniques may have missed.

Although not considered a new methodology, a team applied it to a site in Southeast Asia and reconstructed the ground conditions in the Tam Pà Ling cave site in northeastern Laos between 52,000 years and 10,000 years ago in an article published in Quaternary Science Reviews.

“Our paper puts microstratigraphy at center stage,” says Vito Hernandez, a graduate student at Flinders University in Australia, who participated in the investigation.

What Dirt Tells Us About Ancient Lives

So what does this particular dirt say about the cave and the ancient people who lived in or near it?

“How dirt is built up, or its structure tells a lot,” says Hernandez. “Laterally compressed crusts of dirt suggests that these have been trampled on, perhaps by humans or even animals. A bottom-up stacked series of very reddened sediment, charcoal, burnt bone, and ash suggests that a hearth was built, and that this was likely used for cooking.”

Examining the sediment surrounding the human fossils provides a clearer idea of how they reached their final resting place. The archaeologists’ soil analysis revealed that cave conditions fluctuated from wet to dry, depending on the season.

“This change in environment influenced the cave’s interior topography and would have impacted how sediments, including human fossils, were deposited within the cave,” Mike Morley, a Flinders University professor who participated in the study, said in a press release.

“How early Homo sapiens came to be buried deep within the cave has long been debated, but our sediment analysis indicates that the fossils were washed into the cave as loose sediments and debris accumulating over time, likely carried by water from surrounding hillsides during periods of heavy rainfall,” he said.

Read More: How Archaeologists Know Where to Dig

Arrival of Early Humans in Southeast Asia

The group had previously dated layers from different depths of the cave, which, in turn pushed back the arrival of early humans in Southeast Asia.

Although the technique allows archaeologists to recreate pictures of the past using just a few fragments, it does have limits. For instance, they can’t definitively tell whether some of the ash the uncovered came from cooking or forest fires.

“The environmental context of the ashes need to be studied in more detail, and therefore there is still much more work to do in the site and area,” says Hernandez.

Read More: The Story Of Southeast Asia Through Ancient DNA

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Before joining Discover Magazine, Paul spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.