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Rio Tinto, Spain

The Rio Tinto gets its reddish color from the iron present in its water; scientists have studied its ecosystem because of its similarities to the planet Mars.

demarfa/iStock/Thinkstock

Spain's Rio Tinto river conjures up images of what a river might look like on some alien world that future astronauts had turned into a mining colony.

For thousands of years, generations of miners have dug shafts into the local soil in pursuit of mineral wealth. The Romans fashioned some of their first coins from the Rio Tinto area's gold and silver, and today, the area is one of the most important sources of copper and sulfur on the planet.

But the pollution runoff from thousands of years of mineral extraction has taken its toll upon the river, whose waters have turned deep red due to high acidity, heavy metals and bacteria that oxidize iron and sulfur — life-forms akin to what scientists hope they will find on distant worlds such as Mars or Jupiter's moon Europa [source: Bordenstein].

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