The Ussher chronology is a 17th-century chronology of the history of the world formulated from a literal reading of the Bible by James Ussher, the Archbishop of Armagh (Church of Ireland). The chronology is sometimes associated with young Earth creationism, which holds that the universe was created only a few millennia ago by God as they believe is described in the first two chapters of the Biblical book of Genesis.
The full title of Ussher's work is Annales Veteris Testamenti, a prima mundi origine deducti, una cum rerum Asiaticarum et Aegyptiacarum chronico, a temporis historici principio usque ad Maccabaicorum initia producto. (""Annals of the Old Testament, deduced from the first origins of the world, the chronicle of Asiatic and Egyptian matters together produced from the beginning of historical time up to the beginnings of Maccabes"")
Ussher's work was his contribution to the long-running theological debate on the age of the Earth. This was a major concern of many Christian scholars over the centuries.
The chronology is sometimes called the Ussher-Lightfoot chronology because John Lightfoot published a similar chronology in 1642â??1644. This, however, is a misnomer, as the chronology is based on Ussher's work alone and not that of Lightfoot. Ussher deduced that the first day of creation began at nightfall on Saturday, October 22, 4004 BC, in the proleptic Julian calendar, near the autumnal equinox. He elsewhere dates the time to 6 pm. Lightfoot similarly deduced that Creation began at nightfall near the autumnal equinox, but in the year 3929 BC.
Ussher's proposed date of 4004 BC differed little from other Biblically based estimates, such as those of Jose ben Halafta (3761 BC), Bede (3952 BC), Ussher's near-contemporary Scaliger (3949 BC), Johannes Kepler (3992 BC) or Sir Isaac Newton (c. 4000 BC).[1] Ussher's specific choice of starting year may have been influenced by the then-widely-held belief that the Earth's potential duration was 6,000 years (4,000 before the birth of Christ and 2,000 after), corresponding to the six days of Creation, on the grounds that ""one day is with the Lord as a thousand years, and a thousand years as one day"" (2 Peter 3:8). This view continued to be held as recently as AD 2000,[2][3] six thousand years after 4004 BC.
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All details taken directly from provider content at http://en.wikipedia.org/wiki/Ussher_chronology