By Viv Forbes – Re-Blogged From http://www.WattsUpWithThat.com
Most chapters of human history are defined by the tools and machines that were used.
In the Stone Age, the first tools were “green tools” – digging sticks, spears, boomerangs, bows and arrows made of wood; and axes, clubs, knives and grinders made of stone. These were all powered by human energy.
Then humans learned how to control fire for warmth, cooking, warfare and hunting.