What is the best method of radioactive decay for something that is approximately 48,000 years old?

Sort each of the planetary properties below based on whether they apply to some, all, or none of the four jovian planets in our solar system. jupiter and saturn only: -interior is mostly liquid or metallic hydrogen -composed mostly of hydrogen and helium uranus and neptune only: -blue color because of methane -composed mostly hydrogen compounds all four jovian planets: -approximately 10 earth-mass core -orbited by rings of ice and rock -magnetic field stronger than earth's -strong atmospheric winds and storms no jovian planets: -solid surface under a thick atmosphere