Age earth radiometric dating
Of course, there are many problems with such dating methods, such as parent or daughter substances entering or leaving the rock, as well as daughter product being present at the beginning.
• RATE-Project Claims [about Helium in Zircons] by Rodney Whitefield Radiocarbon Decay (trace amounts of C-14 radiation) • RATE's Radiocarbon: Intrinsic or Contamination?
Most scientists today believe that life has existed on the earth for billions of years.
This belief in long ages for the earth and the existence of life is derived largely from radiometric dating.
(from ICR's homepage for RATE) / For an overview of RATE you can read descriptions, by young-earth creationists, of Thousands not Billions (conference), Thousands not Billions (Radioisotope Age Dating Set, with popular-level book, study guide, two DVDs), Radioisotopes and the Age of the Earth (technical-level book), and a free presentation (video or powerpoint).
You can explore educational web-resources that explain the principles of radiometric dating in the homepage for AGE OF THE EARTH — SCIENCE where you'll see different perspectives (conventional and young-earth) on the reliability of scientific conclusions about the earth's age.