Blue whale, the largest animal to have lived on planet earth, weighs about 1,80,000 kilograms. Interestingly, its tongue can weigh as much as an elephant, at about 2,700 kilograms. The blue whale also has the longest lifespan for a mammal, with an average age of 80 to 90 years. They mainly catch their food by diving, and descend to depths of approximately 500 m.