It's big, it's old and it lives under the sea -- and now an international research collaboration has confirmed that an ancient seagrass holds the secrets of the oldest living organism on Earth. Ancient giant Posidonia oceanica reproduces asexually, generating clones of itself. A single organism -- which has been found to span up to 15 kilometers in width and reach more than 6,000 metric tonnes in mass -- may well be more than 100,000 years old....