How old is the earth? Scientists today believe the universe began with a Big Bang nearly 14 billion years ago, though young earth creationists disagree. While they don't necessarily go along with him in detail, their views are in line with those of Archbishop James Ussher (1581-1656).

Ussher was the Archbishop of Armagh in Ireland during the most turbulent period of modern British history, the terrible Civil War. He was a fervent anti-Catholic Protestant, though a Royalist who supported King Charles; he watched his execution, but fainted before the axe fell.

Ussher believed the creation began on Sunday, October 23. So this isn't just the first day of the week , but the first day of everything.

He published his findings in 1650 in a book called Annales veteris testamenti, a prima mundi origine deducti (Annals of the Old Testament, deduced from the first origins of the world').

But how did Ussher decide on this particular day?

Ussher was a formidably learned man, who understood astronomy, ancient languages and ancient history.

There are long genealogical tables in the Old Testament – see Genesis 5, for instance – that provide a framework for calculating the age of the earth. But that isn't helpful unless you have a starting date. You also have to know which calendar to use.

Ussher also had to decide which text of the Jewish Torah to use, as they gave different figures for the number of years between the Flood and the Creation. In the end he chose the Masoretic version, which gave a figure of exactly 4,000 years before 4 BC, when it's generally accepted Jesus was born; the Greek version, the Septuagint, is 1,500 years out. Furthermore, the Masoretic text gives the Temple of Solomon's completion at 3,000 years after the Creation – so exactly 1,000 years before the birth of Jesus.

He also had to cross-reference the period of the Jewish Kings with events known from outside the Bible, as the chronology isn't clear. Ussher used the Jewish calendar to establish that the Creation began in the autumn – the Jewish new year – on a Sunday near the autumnal equinox. It had to be a Sunday because on the seventh day – the Jewish Sabbath, or Saturday – God rested from his work. He used Kepler's astronomical tables to fix the final date.

Ussher was not the only person to try to fix the date of creation. The Venerable Bede had calculated it at 3952 BC. The Saxons thought it was about 5,200 BC (Bede was accused of heresy for disagreeing). Jospeh Scaliger (1540-1609), the great French scholar, after immensely complicated astronomical calculations, thought it was 4713 BC. Sir Isaac Newton fixed it at 4,000 BC.

But we tend to remember Ussher, and it may be that the reason is just an accident of publishing: from 1701, editions of the King James Bible included his chronology in their margins.

Nowadays, even young earth creationists who take a very literalist view of Genesis would be reluctant to be so exact about the beginning of creation; the furthest they tend to go is that the world is a few thousand years old rather than a few million. But that doesn't mean Ussher and his fellow scholars were simply being foolish. Scientist Stephen Jay Gould – himself an atheist – said his work was "an honorable effort for its time" and that "our usual ridicule only records a lamentable small-mindedness based on mistaken use of present criteria to judge a distant and different past". He said: "Ussher represented the best of scholarship in his time. He was part of a substantial research tradition, a large community of intellectuals working toward a common goal under an accepted methodology."

However, it's fair to say that things have moved on. Scholars – and preachers – today are more interested in the theology of Creation than its date. The Bible tells us that the world was created good, and that we are not the products of blind chance. It tells us we are the stewards of creation, not its masters; it tells us how important Sabbath is. It tells us we are made in the image of God.

Follow Mark Woods on Twitter: @RevMarkWoods