Final answer:
The discovery of 12,000-year-old tools in South America caused scientists to re-evaluate theories of human migration into the Americas, suggesting earlier settlement than the Bering Land Bridge and coastal migration theories for arrivals from Asia previously accounted for.
Step-by-step explanation:
When 12,000-year-old tools were discovered in South America, it prompted scientists to reassess their understanding of human migration to the Americas. Previously, the Bering Land Bridge theory and the coastal migration theory were the most accepted explanations for how the first people arrived in the Americas, suggesting migration from Asia around 20,000-14,000 BP. These theories accounted for human movements over land, following the megafauna of the Pleistocene era, and also potential coastal routes by raft or canoe.
The discovery of these tools indicated the presence of humans in the Americas earlier than the oldest North American sites, creating a challenge for the Bering Land Bridge theory. It suggested that human migration could have also come from directions or via methods not previously considered, or at least that migration and settlement happened earlier than thought. Hence, archaeologists and scientists are continually revising theories as new evidence, such as the 12,000-year-old tools, comes to light.