Terra Preta, or "Dark Earth" is the name for the super-fertile, man-made soil, covering a combined area, the size of France, that has been discovered in the Amazon. The above video and it's accompanying article at
http://news.nationalgeographic.com/news/2008/11/081119-lost-cities-amazon.html gives an excellent synopsis of what it is, and why it's such an incredible and significant discovery.
Terra Preta is now being intensively studied as a hopeful solution to the impending climate and agricultural crises.
Terra Preta seems to have many ingredients that seem to act synergisticly, but the key ingredient is charcoal. Below is an excellent video on how to make your own charcoal, in a non-polluting way, on a family garden-sized scale. The finished charcoal is ground up, and moistened, and mixed 50/50 with compost (and other needed soil amendments), and then it is tilled into the garden soil.