Ancient human faces believed to have been carved into rock up to 2,000 years ago have been revealed in the Amazon.The previously hidden petroglyphs were spotted on a riverbank after an extreme drought last week caused water levels to plummet to their lowest level in more than a century.Most of the engravings on the River Negro – a major tributary of the Amazon – are of facial expressions, some smiling and others looking grim.Several have been seen before but now there are a greater variety it should help to establish the origin of the carvings, experts say.'The engravings are prehistoric,...