"Is that an era or period?"
Translation:זה עידן או תקופה?
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.
We certainly seem to use them sort of interchangeably, but they are used in geologic time frames, with an Eon (several hundred million years) being made up of eras, and then eras are divided into periods (such as Jurassic and Triassic) and periods are made up of epochs, and epochs are made up of ages. The determination is by rock strata, not life forms. So for geologic purposes Eon>Age. For cultural reference, I think most of us would agree that Eons are really long, but the rest get muddled. There is no absolute reference such that an era lasts x-amount of years. Clearly "In our era" cannot mean millions of years, but the relative comparisons might be useful. If someone says, "It's been AGES since we talked." You could actually say, "No, more like an epoch!" You can get more detail by googling geologic time periods.
Well, interestingly the Greek word Eon, αἰών, used a lot in the LXX, is the equivalent of Hebrew עוֹלָם, the time out of mind, be it past or future, which is ultimately eternity, so you cannot use it for the big geological periods, so that you are stuck there with the term עִדָּן too, like עִדָּן הַטְּרִיאַס the Triassic eon.
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?).