Namib desert, Namibia, Africa

Multi-coloured layers of Mereenie sandstone at King's Canyon, Northern Territory, Australia

Petroglyphs carved 1000 years ago by Fremont Native American people in the iron oxide 'desert varnish' on the sandstone of Cub Creek Valley in this fossil park, Dinosaur National Monument, Utah, United States of America (USA), North America

Petroglyphs carved 1000 years ago by Fremont Native American people in the iron oxide 'desert varnish' on the sandstone of Cub Creek Valley in this fossil park, Dinosaur National Monument, Utah, United States of America (USA), North America

Petroglyph of male figure carved 1000 years ago by Fremont Native American people in the iron oxide 'desert varnish' on the sandstone of Cub Creek Valley in this fossil park, Dinosaur National Monument, Utah, United States of America (USA), North America

Iron oxide mine pollution, River Pelenna, Cwm Gwenffrwd, Tonmawr, Mid Glamorgan, Wales, Uk, Europe

Monument Valley Navajo Tribal Park, Arizona, United States Of America

Monument Valley Navajo Tribal Park, Arizona, United States Of America

R?o Tinto, Andalucia, Spain *** Local Caption *** R?o Tinto ("Red River") is very acidic (Ph 2) and has a deep reddish hue due to iron dissolved in water. The acidity of the watercourse is linked to the drainage of pyrite, which is very present in the subsoil. Extremophilic and endemic bacteria and algae colonize the river bed, forming a fragile biofilm that evokes the hot springs of Yellowstone Park in the USA.

R?o Tinto, Andalucia, Spain *** Local Caption *** R?o Tinto ("Red River") is very acidic (Ph 2) and has a deep reddish hue due to iron dissolved in water. The acidity of the watercourse is linked to the drainage of pyrite, which is very present in the subsoil. Extremophilic and endemic bacteria and algae colonize the river bed, forming a fragile biofilm that evokes the hot springs of Yellowstone Park in the USA.