Chapter 3: conflict and conquest: the historic shaping of the canadian landscape. Some scholars have proposed an arrival date as early as 40,000 bp; others most focus on the period between 15,000 and 25,000 years ago. Last ice age was at its peak, some 20,000 years ago; seawater were locked in the ice sheets that covered most of northern north america. Free of ice because of its dry climate, this area was known as beringia. Hunter-gatherers -- gradually made their way south via an ice-free corridor through the mountains. Beringia facilitated the diffusion of many species besides humans, from plants to animals such as caribou, bison, musk, ox, and mammoth. Extinction of some species -- a crucial factor in these events was climate change; warning trend began roughly 15,000 years ago. Nomadic peoples: hunting and gathering groups who moved from region to region in search of food without establishing permanent camps.