if something is a source of something else then that something else comes from that something & the sun is the source of energy for life on earth ->  energy on earth comes from the sun  energy on earth comes from the sun & living things all require energy for survival ->  living things require energy from the sun for survival  living things require energy from the sun for survival & if a living thing requires something for survival then that living thing depends on that something -> living things depend on energy from the sun