Recently scientists 1(found out, has found out, find out, have found out) more about life on planet Earth and now they 2(knew,have known, know, known) better where to look for life in outer space. For a long time, scientists 3(believe, believed, believes, have believed) that life 4(depended,depend,depends,have depended) on sunlight for energy. Then, in 1978,a submarine 5(dive,have dived, has dived, dived) to the bottom of the Pacific Ocean. Although there 6(were, was, has been, have been) no sunlight, and they 7(have found, finds, found, has found) tube worms, clams and crabs, and other life forms.
