Early humans in America endured climate chaos—new research

Around 23,000 years ago, people walked across the muddy edges of an ancient lake in what is now White Sands National Park, New Mexico. Their footprints have provided crucial insight into when humans first arrived in the Americas, dating earlier than previously accepted sites. However, the story of these early humans is more complex than just their presence.

Our latest research, published in Science Advances and Fossil Studies, reveals that these early inhabitants experienced significant climate change during their time at White Sands.

The footprints were found in 20 different layers of sediment, spanning nearly 2,000 years from about 23,500 to 21,700 years ago, during the last glacial maximum. As the sediments were analyzed, a detailed environmental history emerged alongside the footprints. The area was once dominated by a large lake, Lake Otero, with surrounding conifer forests and cold temperatures.

However, this landscape underwent dramatic changes over time. The lake began to shrink as temperatures rose, conifer forests declined, and the environment became increasingly arid, with conifer forests replaced by oak and sagebrush.

This larger climatic shift was punctuated by more abrupt changes, such as a severe drought around 23,200 years ago. During this period, rainfall decreased, the lake became saltier, and drought-tolerant vegetation expanded. Remarkably, these climatic shifts coincided with the earliest footprint layer found at White Sands. The footprints thus offer a snapshot of a world undergoing rapid environmental changes, highlighting the resilience and adaptability of early humans in facing such challenges.

However, the story of these footprints is not straightforward. While they provide a clear indication of human presence, the preservation of these footprints is not uniform. Our agent-based computer model, which simulates human activity around a fluctuating lake, supports this observation. The model demonstrates that footprints are likely to be preserved during environmental transitions, such as periods of drought and subsequent wetting, which create the right conditions for mud to be exposed and then buried by sediment.

This model's findings align with the real White Sands record, where footprint surfaces appear as irregular pulses clustered around times of climatic and hydrological change. This pattern suggests that the presence of footprints is not a direct measure of population size or activity but rather reflects the specific geological conditions at the time of their formation.

The gaps between these footprint surfaces do not necessarily indicate that people were absent; rather, they highlight the limitations of the fossil record in capturing the full picture of human activity.

In conclusion, the footprints at White Sands reveal two intertwined histories: the human history of early inhabitants who lived in this landscape for almost two millennia as the lake shrank, vegetation changed, and the climate swung between wetter and extremely dry conditions; and the geological history that determined which fragments of human life were preserved.

The footprints offer a unique glimpse into the adaptive strategies of these early humans, but they also underscore the complexity of interpreting archaeological evidence, reminding us that recorded history is often incomplete and shaped by the circumstances of preservation.