Before Prithu Maharaja, an incarnation of Krishna, became king of the earth, it was ruled by a demoniac king. Therefore the earth held back her natural resources. After Prithu was enthroned, the earth still refused to deliver her resources. Therefore He became angry at the earth and attacked her. The personified earth took the form of a cow and fled.

(Srimad-Bhagavatam 4.17.9-11)