The number of oxygen-starved dead zones in the world's oceans and seas is rising, according to a report of the United Nations Environment Programme published 29 March-the result of excessive nutrients, mainly nitrogen, from the use of synthetic fertilizers in agriculture, as well as vehicle and factory air emissions. NASA's Opportunity Rover has found that some rocks on Mars probably formed as deposits in a shallow salt flat, or playa, rover science team members announced on 23 March. When scientists announced on 2 March that they had found strong evidence that a rock outcrop in Mars' Meridiana Planum region once was a wet and habitable environment, they had still been uncertain about whether the rocks had been laid down in liquid water. (See Eos, 16 March 2004.)