How do scientists determine the age of fossils?

[GeorgeTFS]

How do scientists determine the age of fossils? Is one method preferred over another? 

[fernandojb]

It depends on the kind of fossil, sample availability, conservation of the specimen and the age of it. For example, carbon-14 dates could be useful for those materiales younger than 40,000 years and well conserved. Uranium-thorium isotope ratios (uranium series) can be measured to estimate the minimum age of fossils younger than 500,000 y. The most powerful techniques for U-Series are based on mass spectrometry MC ICP-MS or TIMS (Thermo NEPTUNE or Thermo TIMS), but not limited to them. Also other techniques can be applied for fossil age determination like Electron Paramagnetic Resonance (EPR / ESR) for certain fossils, and other isotope systems (U-Pb) by ICP-MS techniques are also commonly used for older fossils.