From a Brazilian mine where 50,000 mud-covered men haul heavy bags of dirt up and down slippery ladders in search of a stray nugget of gold, to a former lake in western Africa now swallowed by the encroaching desert, where emaciated, starving people walk over its surface of sand, photographer Sebastião Salgado explores the live of the planet's often ignored people with a critical eye and an empathetic heart.