 Several hundred years later, the climate of Minnesota warmed significantly. As large animals such as mammoths became extinct, native people changed their diet. They gathered nuts, berries, and vegetables, and they hunted smaller animals such as deer, bison, and birds. The stone tools found from this era became smaller and more specialized to use these new food sources. They also devised new techniques for catching fish, such as fish hooks, nets, and harpoons. Around 5000 BC, people on the shores of Lake Superior (in Minnesota and portions of what is now Michigan, Wisconsin, and Canada) were the first on the continent to begin making metal tools. Pieces of ore with high concentrations of copper were initially pounded into a rough shape, heated to reduce brittleness, pounded again to refine the shape, and reheated. Edges could be made sharp enough to be useful as knives or spear points.
