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? uranium-238 rubidium-91 iodine-131 cobalt-60

the only one of these materials that allows studying processes of a very long period of time is Uranium 238

Explanation:

In a radioactive material, half of the atoms decay each life period, in carbon 14 this period T = 5730 years, so for a time of 40,000 years there are 7 life periods, so there are very few atoms left without decomposing .

To study older samples, materials with a longer life period are needed, let's show the visa time

²³⁸U     T=  4.5 10¹⁰ years

⁹¹Rb     T =  58 s

¹³¹I        T= 8.04 days

⁶⁰Co     T= 5.27 years

Therefore, the only one of these materials that allows studying processes of a very long period of time is Uranium 238

see earlier