Well, I'm assuming you're talking about these terms...
Species, Genus, Family, Order, Class, Phylum, Kingdom, Domain
A good way to remember this is;
Does King Philip Come Over For Great Spaghetti
(However, this is in order from most specific to least specific)
A. parasitism. The plasmodium is helped while the human host, harmed.
b. mutualism. The bacteria is supplied with a living environment while the host human is supplied with vitamin K
Radiometric dating depends on radiation from carbon atoms which means only carbon based things can be dated. And life is based on carbon so basically only living things can be dated.