"Is that an era or period?"
Translation:זה עידן או תקופה?
Because עידן is a masculine noun. If it were the other way round, you could use ?זאת תקופה או עידן
So whether I would say זה vs. זאת depends on the first word I list after that?
Yes. If you want to be completely accurate gender-wise you could say זה עידן או שזאת תקופה, but it's a bit long.
Another option, which I'm not sure if grammatically okay but is very common, is just to use זה, since you're not sure what the gender of "that" is (could be either masculine if it's עידן or feminine if it's תקופה). The same way you'd only use זה in "מה זה" (what is that?).
Combination of זה with הוא (copula). So it means something like "this is".
Well, I think עִדָּן is always a particular span of time of historical dimension, like עִדַּן־הַקֶ֫רַח the ice age, עִדַּן־הַזָּהָב שֶׁל טֶלֶוִ֫יזְיָה the golden age of television or עִדַּן־הַגַּרְעִין the nuclear age. But the Hebrew word תְּקוּפָה period of time can mean the same, as the doublet עִדַּן־הָאֶ֫בֶן and the more usual תְּקוּפַת־הָאֶ֫בֶן stone age shows. And תְּקוּפָה can additionally also be a certain stretch of time in a person's life, like in זֶה הָיְתַָה תְּקוּפָה דֵּי שְׁחוֹרָה לְכֻלָּ֫נוּ this was quite a dark time for all of us or זֶה כְּמוֹ תְּקוּפָה חֲדָשָׁה בַּחַיִּים שֶׁלִּי this is like a new phase in my life.