 The presence of people in Mesoamerica was once thought to date back 40,000 years, an estimate based on what were believed to be ancient footprints discovered in the Valley of Mexico; but after further investigation using radiocarbon dating, it appears this date may not be accurate.It is currently unclear whether 23,000-year-old campfire remains found in the Valley of Mexico are the earliest human remains uncovered so far in Mexico.The first people to settle in Mexico encountered a climate far milder than the current one.