TW, quite right. I do need to revise this subject because others like Jeremy are saying Daniel isn't true prophecy and we need to answer that.
Here's what I mean- this is something I had forgotten:
The 70 years spoken of by Jeremiah speaks of the return of the Jews from Babylonian captivity. God decreed that the land of Judah was to lie desolate for 70 years. The book of II Chronicles tells us why their punishment was to run for that particular amount of time:
II CHRONICLES 36:20 And those who escaped from the sword he [Nebuchadnezzar] carried away to Babylon, where they became servants to him and his sons until the rule of the kingdom of Persia, 21 to fulfill the word of the LORD by the mouth of Jeremiah, until the land had enjoyed her Sabbaths. As long as she lay desolate she kept Sabbath, to fulfill seventy years. (NKJV)
As recorded in the 26th chapter of Leviticus, God warned Israel through Moses about this very punishment for disobedience:
LEVITICUS 26:31 "I will lay your cities waste and bring your sanctuaries to desolation, and I will not smell the fragrance of your sweet aromas. 32 I will bring the land to desolation, and your enemies who dwell in it shall be astonished at it. 33 I will scatter you among the nations and draw out a sword after you; your land shall be desolate and your cities waste. 34 Then the land shall enjoy its Sabbaths as long as it lies desolate and you are in your enemies' land; then the land shall rest and enjoy its Sabbaths. 35 As long as it lies desolate it shall rest – for the time it did not rest on your Sabbaths when you dwelt in it." (NKJV)
Apparently Israel did not keep the sabbatical years for a period of at least 490 years (70 times every 7th year). Therefore, God allowed the land to be desolate for 70 years in order for it to observe those neglected Sabbaths.
http://www.herealittletherealittle.net/index.cfm?page_name=70-Weeks-DanielThis shows that the seventy sevens in Daniel 9 should probably be taken to mean a literal period of 490 years.