Launched in 1764 as a coal carrying ship Earl of Pembroke , she was bought by the Navy in 1768 for a scientific mission to the Pacific Ocean . She was also to search for the unknown southern land , Terra Australis Incognita . Launched in 1764 as the collier Earl of Pembroke , she was purchased by the Navy in 1768 for a scientific mission to the Pacific Ocean , and to explore the seas for the surmised Terra Australis Incognita or `` unknown southern land '' .