Conquistadores, exploreres  and archeologists have searched in vain for ancient cities in the amazon basin.  Early European expeditions to the area reported large, well organized  and prosperous garden communities but  modern scientific analysis judged the  soil of the region to be too poor to support agculture and the early accounts to be fiction. Terra preta, dark earth, is the term for deep deposits of black and intensely fertile soil in the amazon basin where  plants grow many times quicker and large.  Deposits are located along rivers and sometimes in areas raised above the floodplain, comprising in total an area about the size of France. Archeological digs have discovered that these areas were created by a thriving and populous culture who raised fish and turtles in ponds and practiced "slash and char" agriculture, where wood was burned in big airless piles and the resulting charcoal incorporated into the soil.          
    Evidently, this culture was so quickly and utterly destroyed by the first European explorers that expeditions returning to the area 50 years later found no trace of the well ordered communities described in first reports. Their few descendants use slash and burn farming techniques, moving from area to area as the soil depletes. In the last few years this discovery has excited archeologists,  soil specialists , organic gardeners and, perhaps most of all climate scientists. James Lovelock, planetary superhero, is excited about this! He says:

           “There is one way we could save ourselves and that is through the massive burial of charcoal. It would mean farmers turning all their agricultural waste - which contains carbon that the plants have spent the summer sequestering - into non-biodegradable charcoal, and burying it in the soil. Then you can start shifting really hefty quantities of carbon out of the system and pull the CO2 down quite fast.”
  

        That got my attention,  so i looked into the subject.  The further i look the more i see,  and the more i see there is the see.  The discoveries in the Amazon show us a way to sequester significant amounts of carbon and revolutionize our agriculture at the same time. Terra preta has been called a "terrestrial coral reef" and it is teeming with biological activity. The process Lovelock was referring to is now called “biochar” and is the subject of tens of thousands of websites, videos, scientific papers and backyard experiments. One website by a guy named Albert Bates, who is all full of enthusiasm from just attending the second annual International Biochar Initiative informs Us that:

“One gram of biochar has a surface area of 1000 square meters. The way it accomplishes this is through micropores, the crystalline-like surfaces formed, randomly and chaotically, during pyrolysis. Terra preta’s carbon sequestration process uses a fractal dimension. In the soil, biochar’s cavities fill up with nutrient foodstocks for microbes, much like a kitchen pantry. The microbes move in, and pretty soon hyphae of fungi appear. The hyphae are a fast road for nutrients and moisture – a trade exchange route to plant and tree roots. Examination of biochar-amended soils a few months after treatment found that vigorous fungal colonization was common.”

"In 1542, the Spanish Conquistador, Francisco de Orellana ventured along the Rio Negro, one of the Amazon Basin's great rivers. Hunting a hidden city of gold, his expedition found a network of farms, villages and even huge walled cities. At least that is what he told an eager audience on his return to Spain. The prospect of gold drew others to explore the region, but none could find the people of whom the first Conquistadors had spoken. The missionaries who followed a century later reported finding just isolated tribes of hunter-gatherers. Orellana's story seemed to be no more than a fanciful myth. "

This excellent 45 min. BBC documentary  tells the story of ancient Amazonian civilization  and modern science.