No. Yes. No.
Work Step by Step
The half-life of C-14 is 5730 years. If the samples are just a few years old, too little carbon-14 has decayed. It would be difficult to distinguish between, say, organic materials from 5 years ago or 20 years ago. Shorter-lived radioactive isotopes must be used. For samples that are a few thousand years, enough carbon-14 has decayed for the technique to be effective. Radioactive dating is most effective when the ages are of the same order as the half-life of the isotope. If the samples are a few million years old, too much carbon-14 has decayed, and there will hardly be anything left. It would be difficult to distinguish between, say, organic materials from 10 million years ago or 100 million years ago. Longer-lived radioactive isotopes must be used. This is discussed on page 631.