It's possible for both dialects to evolve, but at different rates. Present-day Quebecois French is not identical to 17th century French, but it's closer to it than present-day Parisian French is.

You can't just make that kind of statement as a fact without providing any kind of source. Read any text from 17th century, languages have evolved quite a bit on both sides of the atlantic. One big reason why Parisian french would be quite different is that colonization to New France did not come from Paris.

People say this, but I've always thought it was just another piece of pop badlinguistics nonsense that you hear about practically every language. Do you have a reliable source?

Smaller populations very reliably have slower-evolving language. Icelandic is similar to old Norse and old English. Just like you'll hear a lot of Iowan accents in Atlanta but not if you drive 80 miles outside of town.

Believe it or not, there is an entire field called linguistics that studies human language and how it evolves.

Although Icelandic maintains an orthography close to Old Norse, the value of the letters is very different today indeed. The vowel system, for example, has been greatly restructured. Preaspiration became a quality of the consonants.

In terms of lexicon, much of the archaic flavour is actually the result of 19th-century language reformers trying to restore old words. In the meantime, Icelandic had borrowed heavily from Danish.

Indeed, there is the field of linguistics, and scholarly treatments of Icelandic (as opposed to pop-sci presentations of the language as a time capsule like yours) point out that Icelandic has undergone a great deal of innovation like any other North Germanic language.

It's true that languages generally change, but they don't necessarily change equally fast everywhere. See also this answer: https://linguistics.stackexchange.com/questions/4033/do-lang...