DETROIT >> Water covers three quarters of the Earth's surface. Austin Jackson covers the other quarter.That used to be the joke.Now who's going to cover the vast stretches of center field at Comerica Park, since Jackson's been traded to the Seattle Mariners?First crack will go to a combination of Rajai Davis - who has started 348 career games in center, but just five for the Tigers - and minor leaguer Ezequiel Carrera, who was called up after Thursday's trade.