"What is the purpose of life ?"  How many times do we ask our self that question ? I personally have three answers to it.
At one level the question is almost ridiculous. Take for example Elisabeth, a Darwin acquaintance of mine. Every evening without fail, at around 6 PM she walks into the Darwin Sailing Club, climbs on one of the high bar stools on the front veranda, and while sipping a glass of bubbly watches the sun go down behind the horizon of Fannie Bay (which during the dry season is sprinkled with yachts tied to their moorings).
To the best of my knowledge nobody has ever walked up to Elisabeth and asked : "What the hell are you doing there Elisabeth ?" (never call her "Liz", she hates that!) "What is the purpose of this ?"

Likewise if you happen to be in Broome (Western Australia) at the time that the Moon cycle and ocean tide combine in just the right way (about once every 3 weeks) you will be able to observe the Staircase to the Moon, without a doubt the most spectacular Moon rise you will ever experience in Australia. And while you are doing that, rest assured that no-one will ask you "What is the purpose of that ?"

So, at its most basic level the purpose of life is (experiencing) life itself ! It is a unique lifelong opportunity to see, to feel, smell, taste, hear, think, communicate, observe, learn, be aware.
I can not stand this lie, rammed through everybody's throat for centuries by the various religions that life on earth is only a valley of misery and tears, but if you behave you will, upon death, rise up to Heaven (But if you are bad, sorry my boy, it will be Hell for you.).   Mind you, I do believe in a Heaven and a Hell, but they are right here on earth, created by ourselves, the human race. We can't conveniently blame it on an imaginary Devil or a God.

This leads me to the second level of answer to my original question. The purpose of life is also to contribute to it. We can do this by helping to increase the "Heaven region" on our planet and to decrease (and eventually get rid of) the "Hell portion" of it.
Focus on that positive aspect of your character at which you are good.

• If you are a caring person, be caring to others, so that they will stop and think "Hey, I should be a bit more caring too!"
  
  
• If you are a generous person, be generous to others as much as you can, so that they will stop and think "Hey, I should be a bit more generous too!"
  (Remember, its effect will be the same as the gentle flap of a butterfly's wing at one side of the ocean which grows into a strong wind at the other side.)
  
  
• And if you are an intelligent person, share your knowledge and understanding with others, reducing their ignorance, increasing their insights and understanding.   For ignorance is the fuel that feeds the flames which rage in our earthly Hell ! .

Finally at a third level, you, I and everyone else, are tiny tiny contributors to the Evolution process of our Universe. This process started some 15 billion years ago with a Bang, transforming raw energy into simple matter (hydrogen and helium) > > Through the forces of gravity this matter clustered together forming stars > > which became the furnaces that forged and spewed out complex matter (all the other elements like Fe, Ni, Si, O, S, etc.) > > which in turn clustered together into planets like our earth > > where organic matter was formed > > Eventually this evolved (with the aid of sunlight and in the right chemical environment) into primitive organic life * > > then ever more complex life > > which at this point has become life with ever increasing intelligence and awareness of the world and universe around it.

Life on earth has evolved now for around 2 billion years. But it is important to realise that it in all probability will continue to evolve for twice that long. The human species is therefore merely a stepping stone, not a final destination. But we are tiny components of this important stepping stone to which we contribute in two ways. During our lifetime through the influence we exert on others, and into the future with our DNA, and the examples we did set and pass on to our children.

So there you have it, that is what I consider to be the triple purpose of life.