In the absence of sufficient archaeological or genetic data, this study uses linguistic models to calculate an estimated time frame for Homo sapiens' settlement of the Americas. The southernmost point of settlement is marked at Monte Verde, Chile, a site with archaeological evidence suggesting that humans began to descend the Americas from Beringia after 14,500 years before present. Nichols tests and falsifies the null hypothesis that the date ancestral Monte Verdeans began this journey was not before about 15,000 years ago (-a time period after the last glacial era had ended). The results from her calculations about language spread rates suggest that the human entry date took place more than 22,000 years ago, during the height of the glacial era. Furthermore, theories about the glacial maximum blocking inland human movement imply that the entry point would have had to have been before the glacial maximum, or over 24,000 years ago.

Definitions of linguistic terms are provided as well as explanations of the methodology used to obtain language spread rates. Because several languages from the last few thousand years have known geographical ranges and estimable ages, their spread rates can be calculated, and these figures are presented in tables. The author acknowledges factors that would differentiate recent language spread rates from a rate for the linguistic frontier, such as the accelerating effects of social organization and transport as well as distinct mechanisms of spread such as language shift, migration or expansion. It is stated that natural ecology (not cultural context) is the most reliable factor for estimating pre-transport, pre-state land frontier spread rates, and that interior spreads are considerably faster than coastal ones. Using as models the two languages (the Numic branch of Uto-Aztecan and Western Desert from interior Australia) most applicable to the theorized circumstances of the linguistic frontier, its spread rate is estimated in order to find the journey time required to make it to Monte Verde by the date proposed by the null hypothesis. Even using the fastest plausible spread rates, the time required for the language frontier to reach Monte Verde greatly exceeds the time alloted by the null hypothesis.