An oil tanker carrying twice as much oil as was lost by the Exxon Valdez in 1989 split in two today and sank in the Atlantic Ocean, threatening to cause an environmental disaster on the Spanish coast 133 miles away. The tanker “Prestige” first ran into trouble almost a week ago when its hull cracked in a storm; even before today’s development, oil had been pouring from the boat, landing as thick sludge on seashores. Thousands of birds and fish are caked with the stuff, and fishing in the region has been banned. Some observers are hoping that the oil on the now-sunken ship remains encased in containers or that cold temperatures will solidify the oil and keep it resting on the ocean floor. Environmentalists and many fishers, however, weren’t so hopeful. Maria Jose Caballero of Greenpeace said, “It’s a time bomb at the bottom of the sea.”