Sentence:  bursting from the lips of a charging cavalry trooper was the last sound heard on this <WSD>earth</WSD> by untold numbers of Cheyennes , Sioux and Apaches , Mexican banditos under Pancho Villa , Japanese in the South Pacific , and Chinese and North Korean Communists in Korea . 
Meaning of the word marked with <WSD> tags:  the 3rd planet from the sun; the planet we live on