The United Nations says it'll take at least 25 years to

clear up

pollution from oil operations in the Ogoniland region of Nigeria. A report by the UN Environment Programme said oil spills had contaminated land, sea and air to such an extent that it seriously threatened public health in some areas. A spokesman for the UNEP, Nick Nuttall, told the BBC about the scale of the problem.

"The United Nations Environment Programme over 14 months has toured the length and breadth of Ogoniland to assess the oil pollution. It is serious.

It has gone much further and much deeper into the land than previously had been supposed.

It's going to take at least 25 years to

restore

the health of Ogoniland back to pre-oil days."

Riot police in the Chilean capital Santiago have used tear gas and water cannon to break up protests by students. More than 100 people were detained as they tried to march to the city centre. Chile has endured weeks of protests by students and teachers demanding education reforms. They've called for

fundamental

reform and increased investment in the public education system. President Sebastian Pinera has offered extra funding.

Scientists have found what they believe may be the first evidence of flowing water on Mars. Nasa researchers say images taken by one of their spacecraft show clusters of dark lines on some slopes of the planet. These markings disappear in the winter. The scientists say their best explanation for this is the flow of salty water, possibly underground, although they say the findings don't provide direct evidence of water on Mars.