You are right, God was NEVER on earth. The one that came to earth to give his life as ransom sacrifice was his first born son, Jesus. This is father and son, two distinct and separate individuals, not the same, as trinitarians believe. It is clearly seen in these two scriptures:
John 3:16 "For God loved the world so much that he gave his only-begotten Son, in order that everyone exercising faith in him might not be destroyed but have everlasting life." John 17:3 "This means everlasting life, their taking in knowledge of you, the only true God, and of the one whom you sent forth, Jesus Christ."