Agence France-Presse: US actress Sigourney Weaver marked Earth Day on Thursday by taking on the role of a real-life environmentalist, urging lawmakers to take action to stop the world’s oceans from turning into deadly acid baths. “I’ve done enough science fiction to know that our Earth will survive through various nightmare scenarios,” Weaver, who played a feisty environmentalist in James Cameron’s blockbuster movie “Avatar,” said at a Senate hearing on ocean acidification, which is caused by carbon …