The unstable isotope nickel-59 can be used to date rocks that contain it. nickel-59 decays into the more stable cobalt-59. the nickel isotope has a half-life of 76,000 years. which statement about nickel-59 is true? a) after 76,000 years, all the nickel-59 in a rock decays into cobalt-59.b) nickel-59 can only be used to date rocks that are younger than 76,000 years. c) all the nickel-59 stabilizes after it completes one half-life period of 76,000 years. d) the amounts of nickel-59 and cobalt-59 remain the same over a half-life period. e) the amounts of nickel-59 and cobalt-59 tell how long ago the rock cooled to closure temperature.