This topic reminds me greatly of my old topic,
What Really Matters? But that topic is in a more spacial regard while this one is in a temporal one. Can they answer be any different? If you as one human lived forever on Earth would you still say you or your life has some special so-called 'purpose' or 'meaning' considering how tiny you are spatially? If it turned out that actually the Earth was flat and the existence of outerspace was a hoax but you still were mortal and would be dead in a 100 years or so and forgotten in time, would that allow your life to have this special so-called 'purpose' or 'meaning' considering your existence would be tiny temporally speaking and you would eventually be forgotten for longer than you were alive or remembered? It seems to me this special so-called 'purpose' or 'meaning' is impossible without one living forever in a spatially tiny universe. If one can at least find importance and value in some sense of the word despite being small spatially then I think one can do it temporarily, but I think it is easier to start with the first as thinking in terms of time is not only more complex but raises one's strong instinctive and perhaps irrational fears of death.
Nonetheless, I suspect the conclusion that one's life or even humanity itself is completely purposeless and meaningless in either case stems from a
false dichotomy fallacy. One seems to think that if one cannot have this super-special purpose or meaning in the strictest most extreme universal sense that then one is purposeless and meaningless. Those who point out the various potential forms of subjective meaning and purpose are only directing hitting at that fundamental fallacy by pointing out with an example that there is other options besides those implicitly or explicitly implied by this false dichotomy fallacy. This false dichotomy fallacy is particularly remarkable because it first requires only considering the potential for purpose or meaning in the most universally extreme sense if not inherently impossible at least so unlikely even hypothetically to be absurd, and then concluding from the lack of that most extreme, unlikely, absurd form of meaning or purpose that the other extreme--perhaps as absurd or even more absurd--that nothing we do matters at all in anyway and has no purpose or meaning and that we might as well commit suicide by self-starvation now because there is no point in eating or anything we do. This is uniquely fallacious like assuming that there are no 5-ton big talking blue ducks with spaceships that there are no ducks at all in that not only is it false dichotomy fallacy but it is an especially misleading one by making us choice not only between a falsely limited number of options but by making at least one of the options patently absurd as to make the other the only option. (Please note, I'm not accusing anyone of being intentionally dishonest or misleading or accusing anyone of being especially illogical, but rather think this is a common extreme fallacy many if not most if not almost all people are prone to make on their own.)
Personally, I do not care much what happen on planets like Jupiter or Mars or the various extrasolar planets, but I care very deeply in some cases about what happens on Earth particularly in certain places. Importance of course is subjective, and thus provides for a special kind of locally subjective so-called meaning or purpose. The same goes for time. I care about what happens here and now, not a billion years from now. The fact that what happens in a billion years on Earth doesn't matter much to me or anyone I know--at least not nearly to the degree as what happens now on Earth--does not make what happens now also unimportant to me anymore than the fact that I do not care much about the day-to-day happenings on Pluto and all other planets means I care less about what happens on Earth.