Nishat Ahmed HW #1 Aim: How did Native American peoples respond to their environment? 1. The Shaping of North America ? Western North American mountains were born 135 to 25 million years ago, after the continent took on its separate identity. ? Canadian Shield - a zone undergirded by ancient rock. This anchored the northeastern corner. ? Great Ice Age took place 2 million years ago. ? When the glaciers retreated about 10,000 years ago, they left North America as we know it today. 2. Peopling the Americas ? Most people probably came to the Americas by land. ? The Ice Age caused sea level to drop and exposed a land bridge connecting Eurasia with North America. ? As sea levels rose, the land bridge inundated.