It's a matter of faith.
Good luck getting them to admit it, though.
It's a matter of some fairly complex, but well tried and tested, chemical and radiological techniques.
Your average mainstream media science article isn't going to take about 10 pages filled with chemical formulas explaining how rocks and fossils are dated EVERY single time they mention some date from a scientist that annoys some idiotic Young Earth Creationist because it's older than 6,000 years.
In terms of the popular press probably the most extensive and understandable explanation of dating of rock is in the "Crossing the Craton" section of John McPhee's "Annals of the Former World."
1. It reminds me of what Mecca should look like if there's another 9-11 type attack.
2. Danny and geezer - go pick your fight on one of the evolution/creation threads.
Please stop repeating lies.