'Seventy Years' in the Bible

Then the Angel of Jehovah answered and said, O Jehovah of Hosts, how long will You not have mercy on Jerusalem and on the cities of Judah against which You have cursed these seventy years?

Speak to all the people of the land, and to the priests, saying, When you fasted and mourned in the fifth and seventh months, even those seventy years, did you truly fast to Me, even to Me?