One light ring plus one dark ring signifies one year of a tree’s life. Embedded in these rings is information about the climate in which the tree has grown, each circle a snapshot of the past. Hominins have time machine rings too, although they are trickier to spot. In a study released Wednesday, scientists gain incredible insight into the day-to-day lives of Neanderthals by examining where these rings take root: in teeth.

This study, published in Science Advances, is the first to use teeth to examine the influence of ancient climate on hominin development. The teeth the team analyzed came from three individuals, all uncovered in the same archeological site in the southeast of France: two Neanderthal children that lived 250,000 years ago, and one modern human child who lived 5,000 years ago. With the human child’s teeth serving as a point of comparison, the team discovered that Neanderthal children appeared to live especially harsh lives, marred by intense environmental elements.

Study co-author Shara Bailey, Ph.D. is a New York University associate professor of evolutionary anthropology. The Neanderthal teeth, she tells Inverse, reveal that the juveniles lived through some rough climatic times in which they “experienced stressful events that affected their development during the winter when resources would have been low.”

The fact that these harsh experiences are literally written in their teeth gives a glimpse into the day-to-day aspects of Neanderthal existence.

“It is difficult to make general statements about Neanderthals as a whole, given that this is a very limited study,” Bailey says. “However, these results suggest that the groups in which these individuals lived did not have sufficient cultural buffering, like food storage, that could have protected the children from nutritional or other environmental stressors.” Her colleague and the lead author Tanya Smith, Ph.D. explains how tiny teeth revealed so much information in the video below.

An explanation of the teeth examination process.

In the rings of the teeth, she and her team found barium, lead, and oxygen, which recorded each individual’s history of nursing, weaning, chemical exposure, and seasonal climate variation. As a tooth grows during fetal and childhood development, a new layer of trace elements is formed every day. Each “growth ring” pulls in the chemicals that circulate the body, and because the rings grow in layers, they reveal a chronological record of exposure.

The oxygen isotopes in the Neanderthal teeth revealed that these children lived through very cold winters and more extreme seasonal periods than the modern human child.

“What I find the most fascinating about this study is the amount of information we can derive about an individual’s life by analyzing what’s in their teeth,” co-author and Mount Sinai Icahn School of Medicine assistant professor Christine Austin, Ph.D., tells Inverse. “We were able to go back in time, 250,000 years, and pinpoint the seasons in which these individuals were born, nursed, and weaned, and when they got sick or were exposed to toxins like lead. That’s a lot of information from some very old teeth!”

Neanderthal tooth
A 250,000- year old Neanderthal tooth yields an unprecedented record of the seasons of birth, nursing, illness, and lead exposure.

One set of the Neanderthal teeth also contained elevated barium, which is directly correlated to consumption of breast milk. It indicated that the child was born in spring and was nursed for about two and a half years. While this may seem like a long time — the World Health Organization that babies exclusively nurse for six months — traditional modern humans who live in hunter-gatherer environments also tend to nurse their children for the same amount of time. This breastfeeding time period, the scientists reason, is perhaps a link between living populations and Neanderthals.

What truly surprised the researchers was discovering that both Neanderthal children were exposed to lead, which has never been documented before in prehistoric samples. Traces of lead in the teeth demonstrate that these children were exposed to lead at least twice during the deep winter or early spring. There’s still some speculation to how these children became exposed to lead in a pre-Industrialized world, but the scientists do have some theories.

“Lead mines are relatively close to the area where these teeth were found, so it’s likely there was a small amount of lead in the food and water these individuals ingested throughout their time there,” Austin explains. “The intense, short duration exposures we saw could be due to another source specific to the cooler seasons, such as to fires that contained lead containing wood or other materials.”

This handful of teeth paints a picture of what it meant to be a Neanderthal child, living in a harsh environmental world where the overarching rule was adapt or die. Seasonal stressors live on in the teeth of those ancient humans, little clues about our relatives huddled in the cold.

“I continue to marvel at the details on nutrition, stress, and weaning we can glean from fossil hominin teeth,” Bailey says. “The finding of lead was particularly surprising and I hope we can follow up with additional studies to explore this in other individuals.”

Photos via Tanya Smith, Tanya M. Smith/Griffith University