The meaning of life

Yes, that stupid question that's caricaturised in so many situations it's become a cliché.
Nonetheless, I would say it's a good start.
I try to view the world scientifically, so for that to happen we must first get out of the way the religious explanation. That explanation is that God put us on earth to look after his creation. If that's true I can imagine he just gave up when we hit the industrial revolution....
Anyway, this ties in with an interesting theory that I'll explain later, the ancient astronaut theory.
It's a stupid idea that I might explain in a later post.
If I feel like it.

Scientific reasons for existence
Scientifically, nothing needs a reason to exist. It just does. However, the very molecule of life, DNA, seems to have a meaning for us as its vehicles. Deoxyribonucleic acid is an interesting and unique chemical. Humans are now able to engineer chemicals, that is, they can take individual atoms and design on a computer a molecule that will do a specific job. This is how most polymers (plastics) were discovered and how "smart" materials are designed. Now, if you were to create an ultimate engineered chemical, the one that would be the hardest to make and also the awesomest, it would be DNA.
Why?
well, why do we exist? we exist because DNA. Yes, DNA which was "accidentally" (depending on what version of the bigger picture you subscribe to) made in that pool of primordial meteorite slime and just happened to have the perfect composition that gave it a sort of "intelligence" that then led to create everything that we know as "alive". DNA works on 2 rules: divide and occasionally mutate. With these two simple rules over millions of years DNA has evolved into you, me and all the pointless creatures that live forever alone under various rocks. This molecule IS us. it is life itself. Scientifically, your soul, or your essence of existence is this DNA. In this sense there is life after death, but that life doesn't continue on when you die, you continue when you knock up a potential partner. Your children are your continuity, and we are just a very VERY complex tool for DNA to replicate itself. In essence, we are all huge dicks.

Ancient astronaut theory
If science left you feeling like a penis and this disappoints you, then you can always turn to religion. While depending on which religion you choose or don't have a choice in you may feel more or less satisfied. Nonetheless, I won't touch on religious beliefs because everyone has their own and these are often kept very close at heart. Instead, I'll offer an alternative reason for being that should satisfy the pious and infidels alike. See it as a story if you wish.
This crackpot theory, I imagine, was suggested for fun many many years ago over a few beers in some bar in Kent. From there it reached the ears of a handfull authors who wrote books on the matter and the idea reached cult status. The gist of it is that we were at some point in the past visited by aliens from space. It sounds strange but the insane thing about it is that it makes almost perfect sense  as in it's very difficult (some claim impossible) to disprove it and it provides a logical explanation that links every ancient religion in the world. But more on this later.
As I mentioned earlier, followers of Jesus would tell you that we were put here by the almighty to look after all the little critters that scurry around not being able to look after themselves the silly things. The AA (please excuse the abbreviation I feel ridiculous writing the name in full) theory would suggest that this was why aliens perhaps genetically enhanced the species on earth known as homo erectus (if that didn't make you snigger read it again) into homo sapiens. This sorta makes sense if you are willing to believe in aliens. Why does it make sense? because it fills in that little gap in evolution known as the missing link (although I think I found it reading youtube comments)
So why did they do this?
possibly for fun. I know that's why I've done almost every single worthwhile and otherwise thing in my life. But to keep in line with what I was saying in the last paragraph, let's say they did it to see how we would develop so that they could monitor and study us, to see when or if we are ever gonna figure out that we don't really have any other place than this planet and stop shitting in our cot.
Alternatively, they might perhaps have had bigger plans for us...

universal conscience
Picture this. with current growth rates, in 600 years we will need 3000,000 Earths just to accomadate the human race. That's with every family having 4 kids (which is about the average taking into account countries where multiple children are essential to any children at all, so don't judge) that means that families double with every generation and if a generation gap is about 17 years average with a current global population of around six billion; well, you do the maths.
The point is that sooner or later we will have to look into interplanetary colonisation. No, inter-stellar. If you want an idea of what that would look like, imagine the Europeans conquering America all over again, except 10 billion times the scale. Inter-stellar colonisation leads to a humongous growth rate and humans could, given a few billion years, colonize our galaxy. Technology also is growing exponentially and with that, our influence on our surrounding universe is also growing exponentially. Where is this leading us? well, the universe is slowly but surely rushing towards total enthalpy. Enthalpy is disorder. The universe is heading towards total disorder, a soup of nothing but light particles floating around in a constant fog of what used to be matter and molecules. Everything is broken down to it's elements and everything is the same, like wonderful and complex coral reefs becoming sand over time. Why does enthalpy do this? Well, there are a million ways for a room to be messy, but only one way for it to be tidy. Set off a small bomb a million times in your room and you might have a small chance of getting it perfect. But this doesn't seem realistic, because you can tidy it yourself, right? Exactly. you are conscious. you have control over your surroundings and therefore you are the only thing in that room that can fight enthalpy. Like yo momma said, your room won't tidy itself up so clean that shit up boy. In this way, presuming that we are the only concious beings in the universe, (not that it matters come to think of it) humanity is the only thing in the universe that can save it from total fuckdom.


Summary
Whatever you get your daily dose of answers from, my personal opinion on the meaning of life is make your own.
Whatever reason we exist or whatever the purpose of humanity as a whole is, your personal reason for existence is what you want to do with your life! whether it's to help others, leave your mark on history or just settle down and have kids, the purpose for you existing is to live. Too many people have worried about why they live and have ended up being consumed by this pondering and lost the essence of living itself.
well, not really.
The truth is that this is a dream and you're actually a fat amorphous lump of a human being in a machine that's being used to process alien shit. You're all just livestock at the end of the day ;)