Rating is available when the video has been rented.
This feature is not available right now. Please try again later.
Published on Apr 16, 2009
For trade, humans overcame numerous obstacles--seas, deserts and mountains. First with rudimentary and then increasingly evolved means. By taming animals such as donkeys, horses and camels, humans were able to travel vast distances. When muscle power was no longer enough, oil and other types of fossil energy sources took over to fuel trains, trucks, cargo ships and airplanes that carry merchandise in ever larger quantities from one side of the globe to the other.