Curious are you? Well you could try the links I gave you.
How Archbishop Usser worked out the age of the Earth.
Below is an excerpt.
The Bible gives some large time periods which enable us to do the same calculations as Ussher, without going into all the intermediate details as he did.
From when Abraham left Haran to enter Canaan and Egypt until the Exodus, exactly 430 years to the day (Genesis 12:10, Exodus 12:40, Galatians 3:17). 2513
Exodus to start of Temple, 479 years (1 Kings 6:1, in the 480th year or after 479 years). 2992
Start of Temple to division of the Kingdom, 37 years (Solomon reigned 40 years, 1 Kings 11:42, temple started in his 4th year). 3029
Division of the Kingdom to destruction of Jerusalem, 388 whole years, plus part of two years (Ezekiel 4:4–6). 3417
Kingdom fell in 588 BC Hence date of creation = 588 + 3417 - 1 = 4004 BC This gives a rough idea of how Ussher did his calculations.
Astronomy and Ussher
Astrogeophysicist Dr John Eddy, who was at the time Solar Astronomer at the High Altitude Observatory at Boulder, Colorado, made some revealing comments at a symposium in 1978, as reported in Geotimes 23:18, September 1978. ‘There is no evidence based solely on solar observations, Eddy stated, that the Sun is 4.5-5 x 109 years old. “I suspect,” he said, “that the Sun is 4.5-billion years old. However, given some new and unexpected results to the contrary, and some time for frantic recalculation and theoretical readjustment, I suspect that we could live with Bishop Ussher’s value for the age of the Earth and Sun. I don’t think we have much in the way of observational evidence in astronomy to conflict with that.”’