Background of Evolving European Chronologies and Present Debate

The study of early human migration into Europe has seen significant advancements over the past four decades. Initial findings from the 1980s placed the earliest human presence in Europe at approximately 0.7 million years ago (Ma). However, more recent discoveries have extended this timeline back to as early as 1.8 Ma in regions such as the southern Caucasus and 1.7-2.1 Ma in China. In Europe, precise dating of these early sites has been challenging due to the absence of volcanic materials for radiometric dating, limited magnetostratigraphic studies, and other constraints. This has led to a prolonged debate about the actual timeline of the first human arrival in Europe.

The Orce Sites

The Orce region in southeastern Spain has been a focal point for studying early human presence. Located in the Baza Basin, this area is rich in Early Pleistocene sedimentary strata and vertebrate fossils. Initial excavations in the 1980s at Venta Micena uncovered what was believed to be a human skull fragment, sparking controversy over its classification. Subsequent findings, including additional human bones and stone tools, further supported the presence of early humans in this region.

Methods

Geological Mapping of the Orce Region

A comprehensive geological map of the Orce area was developed, detailing the distribution of lithostratigraphic units and paleontological sites. This map is essential for establishing a chronostratigraphic framework for the region.

Lithostratigraphic Correlations

Stratigraphic sections were measured at various paleontological sites within the Orce region. These sections were correlated using key marker beds, polarity boundaries, and other stratigraphic criteria. This correlation helps in understanding the vertical and lateral distribution of different lithostratigraphic units.

Paleomagnetic Methods

A detailed paleomagnetic study was conducted on the Orce sedimentary sequences. This involved collecting samples from various stratigraphic levels and analyzing their magnetic properties to identify different magnetic polarity zones. This analysis helps in dating the sedimentary sequences by correlating them with known geomagnetic polarity timescales.

Micropaleontology

Rodent paleontological collections from the Orce sites were studied and compared with other Early Pleistocene localities in Europe. The measurements and comparisons of rodent molars provide additional biostratigraphic data to refine the chronology of the Orce sites.

Results

Geological Mapping and Stratigraphy

The new geological map for the Orce region provides greater accuracy in correlating stratigraphic sections. The map distinguishes between different lithostratigraphic units, which have been associated with specific faunal assemblages and geological features.

Magnetostratigraphy

The paleomagnetic analysis identified five magnetic zones within 80 meters of sedimentary strata, placing all paleontological and archaeological sites in the Vélez Valley between two normal zones. This sequence includes a normal zone correlated with the Olduvai subchron (1.93-1.77 Ma) and another with the Jaramillo subchron (1.071-0.991 Ma). The presence of these magnetic zones helps refine the age of the hominin sites within the Orce region.

Biostratigraphy

The paleontological data from the Orce sites, particularly the rodent assemblages, provide important chronological information. The presence of different species of rodents at various stratigraphic levels helps establish a more detailed timeline for the Early Pleistocene faunal succession in the region.

Bayesian Age Model

A Bayesian age-stratigraphic model was implemented to estimate the ages of the archaeological sites. This model, which considers all available chronostratigraphic data, indicates that the hominin sites of Venta Micena, Barranco León-5, and Fuente Nueva-3 were occupied between 1.32 and 1.23 Ma.

Discussion

Implications for the Oldest European Hominin Record

The findings from the Orce region provide the oldest and most accurately dated evidence of early human presence in Europe, suggesting that hominins arrived in southern Europe around 1.3 Ma. This arrival predates the known occupation of northern European sites and indicates a significant migration event from Africa to Europe through the Strait of Gibraltar.

Asia Occupied Before Europe?

The study suggests that the early human migration into Europe occurred after their settlement in Asia. The geographical barriers, such as the Mediterranean and Black Seas, as well as the climatic conditions in northern Europe, likely delayed the westward expansion of early humans into Europe.

Conclusion

The Orce region presents a unique and significant record of early human occupation in Europe, dating back to approximately 1.3 Ma. The integration of geological mapping, paleomagnetic analysis, and biostratigraphic data provides a robust framework for understanding the timing and sequence of early human migration into Europe. This study highlights the importance of the Orce sites in the broader context of human evolutionary history.

Read the whole research here: Magnetostratigraphic dating of earliest hominin sites in Europe