'Seventy Years' in the Bible

Then the LORD's angel gave answer, and said, 'O LORD of Hosts, how long wilt thou be unmerciful to Jerusalem and to the cities of Judah, with whom thou hast been displeased now these seventy years?'

"Speak unto all the people of the land, and to the priests, and say, 'When ye fasted and mourned in the fifth and seventh month, now this seventy years, did ye fast unto me?