Soru

In her 2018 study of Tiwanaku migration patterns in the middle Moquegua Valley, bioarchaeologist Elena Rostova analyzed strontium isotope ratios ($^{87}\text{Sr}/^{86}\text{Sr}$) preserved in human dental enamel to reconstruct individual residential mobility. Unlike bone tissue, which continuously remodels throughout an individual's lifetime, permanent tooth enamel mineralizes during early childhood and retains a permanent geochemical signature corresponding to the local geology of the water and food consumed during infancy. Rostova’s team established a baseline geological isoscaping map of the Moquegua drainage basin, identifying distinct isotopic boundaries between the high-altitude Altiplano interior ($^{87}\text{Sr}/^{86}\text{Sr} > 0.7095$) and the lower coastal valley ($^{87}\text{Sr}/^{86}\text{Sr} < 0.7078$). The isotopic sampling revealed that nearly thirty percent of the individuals interred in the peripheral Chen Chen cemetery possessed enamel signatures matching the high-altitude Altiplano rather than the local coastal valley baseline. However, while previous scholars posited that these individuals were seasonal agrarian laborers who migrated temporarily to the valley, Rostova observed that their isotopic ratios showed no progressive geochemical shifts across sequential molar tooth cusps, demonstrating that these individuals spent their entire childhood in the Altiplano before migrating permanently in early adulthood.

According to the passage, which of the following is explicitly stated regarding the strontium isotopic ratios measured across sequential molar cusps in the high-altitude migrants?