According to Doctor of the Church the Venerable Bede, the Earth was created today in 3952 BC. Bede was criticized for his conclusion, not because it was revolutionary, but because the calculations he used were considered heretical by the Church. Bede would probably be surprised to learn that the age of the Earth continues to be a source of debate today, both in religious and scientific circles.
Estimates of the age of our planet date back to before the birth of Christ. The 6,000-10,000 year estimate that some creationists argue in favor of today came first from St. Jerome, an Italian priest and scholar who declared, sometime around 400 AD, that the Earth was created four millennia before the birth of Christ. This is almost the same conclusion Bede reached some three centuries later, although Bede's methods, as we mentioned before, were more controversial.
The 4000 BC timeline survived for more than a thousand years after the death of Bede, and was subsequently reinforced by great scientists and scholars of every century. Not only did these men restate the belief that the Earth was less than 6,000 years old, but they attempted to give the act of first creation a date. In 1642, Dr. John Lightfoot, the Vice-Chancellor of Cambridge University, stated that man was created at 9 AM. Two years later, he wrote that it was 9 AM, Sunday, September 12, 3928 BC.
The most famous scholarly estimation of the age of the Earth comes from Anglican Archbishop James Ussher of Dublin, Ireland. In 1650, he published a book entitled "Annals of the Old Testament" in which he claimed the world was created on Sunday, October 23, 4004 BC. This date was later included in the King James Bible in the margins of the Book of Genesis. The notations remained there for centuries and came to be considered canonical by many Christians.
Archbishop Ussher arrived at his conclusive date by using the Hebrew Bible, since other versions gave different ages for the male lineage from Adam to Solomon. This lineage constituted what Ussher called the Early Times. The Early Age of Kings, which ran from the time of Solomon to the destruction of the Temple in Jerusalem, was computed using the length of various kings' reigns as found in the Bible and historical records then available. The Late Age, which ran from Ezra to the birth of Jesus, was probably the most difficult to measure; Ussher had to link events in the Bible with scant records from Middle Eastern society. After all this computing was done, Ussher added four years to his total because of the belief that Jesus had actually been born in 4 BC (we have Dionysius Exiguus, or Dennis the Small, to thank for this little counting error). In the end, he came up with 4004 BC as the year of the creation of the world.
During the 17th century, European naturalists began to conclude that the age of the Earth differed from what the Church had taught for more than a thousand years. Although ancient peoples such as the Greeks had studied fossil remains at differing levels below the ground, it was not until the end of the 18th century that these strata were used to calculate the age of the planet. British naturalist William Smith and his student John Phillips calculated, in the 1790's, that the Earth was about 96 million years old.
Over the course of the next hundred years, various means were developed by which scientists tried to discern just how long creation had been around. One popular method was to build a model closely resembling the Earth at the moment of creation and then compute how long it would take for the sphere to cool down to a habitable temperature from a molten ball of rock. This theory had several gaping holes in it, not the least of which was the fact that heat generated by radioactivity was not discovered until the turn of the 20th century.
Other methods were employed over the years, such as computing how long land erosion had to occur to bring the oceans to their present levels of saltiness. Each theory presented a different age, from 75,000 to over 100 million years. It took the discovery of radioactive decay in the last decade of the 19th century for a method to finally arrive that could rightly claim to be highly accurate. To this day, radiometric dating continues to be the way scientists measure geologic time.
Today, most scientists accept the age of the Earth as being 4.55 billion years. This date was first arrived at in 1956 and has held up well to most scientific scrutiny. But as with all things, there are people who question the methods by which this number was determined.