Are mixtures pure substances that cannot be changed into smaller substances?

Idon’t know the answer and i’ve been stuck on it for a while now skskskskks

Which set of terms best describes a community of miners who live out in the countryside of west virginia and use specialized geological equipment to analyze the composition of rock?

Ihave no idea how to solve these. plus there's another question that is 2) a 10 kilogram meteorite is collected in space and brought back to earth. it is composed of 1.25 kg of uranium-238 and 8.75 kg of lead-206. how many u-238 half lives have passed? what is the approximate age of the meteorite?