The carbon in their bones allow them to know what time period it comes from. This is called carbon-dating.
Zia used hypothetico-deductive reasoning.
The Hypothetico-Deductive method is a scientific model of reaserch. You make a hypothesis of what the problem is - keep in mind that, according to Einstein's thoughts, these hypothesis cannot be 100% verified, they can only be proven wrong - and once you have that, do deduce what the consequences might be.
The function of the semi permeable membrane is to allow substances to diffuse (transport) across it, because its only semi permeable the substance are able to cross. If it was a non permeable membrane it wouldn't allow the transport of substances.