Carbon-14 is the typical radioisotope used to date materials; however, it has a limitation to 40,000 years. A scientist who wants to date materials older than 40,000 years would most likely use which radioisotope?

To date materials older than 40,000 years, the scientist needs an isotope with a much longer half-life than carbon-14. Uranium-238 has a half-life of about 4.5 billion years, so it can be used to date very old materials. The other listed isotopes decay much more quickly.

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