To believe in a YEC-style 6000 year old earth, you'd have to ignore evidence from nearly every corner of the sciences. The original evidence for an old earth came from geological processes like river sedimentation, but even stronger evidence is available today from continental drift and radioactive decay rates. Essentially all the earth's helium, for instance, comes from the radioactive decay of heavy elements with half-lives of millions of years; if the earth was only thousands of years old, then virtually none of these atoms would have decayed yet. In biology, the great age of the earth is demonstrated by rates of change of DNA. Historical linguistics shows that many modern languages evolved from a smaller number of parent languages, and the rate at which languages change is too slow to allow this linguistic evolution to have occurred within 6000 years. There is also a great deal of astronomical evidence. Measurements of the rate of cratering in our solar system show that the moon must be billions of years old. The ages of star clusters can be determined based on models of how the structure of a star changes as it uses up its hydrogen fuel.