Comment Carbon dating... (Score 1) 336
ahref=http://en.wikipedia.org/wiki/Carbon_datingrel=url2html-21275http://en.wikipedia.org/wiki/Carbon_dating> only works for things up to ~50,000 years old, so it wasn't used for those old rocks. For things older than ~100,000 years folks use ahref=http://en.wikipedia.org/wiki/Potassium-argon_datingrel=url2html-21275http://en.wikipedia.org/wiki/Potassium-argon_dating>. The applicable time period is based on the half-life of the isotope. Carbon-14 has a half-life of 5730 years while Potassium-40's is 1.248e9 years.