purpose of this life

A good friend of mine posted the same question to our group “ what is the purpose of this life?” . We are a group of friends who have studied together so generally open books to each others. "Jindagi na milegi dobara" was the first response, live it to the full, least you regret it later. Few of us just checked on the health of the questioner, to pose such questions too early in life. It pushed me deeper in my thoughts  but other posts and the routine drowned the essence of the question.
Is there any purpose of this life? I, some times back, read Paulo Cohelo’s The Alchemist, where the boy knew his destiny and his purpose was to reach it. Must be a lucky guy at least someone told him and he followed it in letter and spirit. But  is the purpose of our life is to reach ones destiny? I had read somewhere we are here on this earth for a specific cause, purpose, like Ram was here to defeat Ravana, Krisna was here to give Bhagwad Gita, Jesus, Guru Nanak, Mohammed they all had a purpose. Were they told at birth or sometimes later the purpose of their lives or its their action at certain critical situations made them the GODs. 
My mind drifted towards the discovery channel and saw how the tigers are responsible for maintaining the ecological balance of the environment. Each and every living being was part of the ecosystem and every living being had some purpose. But we human beings aren't part of the system, in fact we are the ones who destabilise or unbalance the ecosystem. May be, that could be our purpose.
So the question itself is incorrect. Some one may whisper it in your ears, but then its up to you firstly to believe in it and how far you can reach with it. I doubt anyone did it for the great people we read of and any one who tells you about it may have his own motive behind it.
The mind is always searching, searching for food when hungry, searching for water when thirsty, searching for friends when lonely, searching for a shelter when in trouble, searching for a place to retire when tired. Its that search be it knowledge, pleasure, power, satisfaction which will decide your path.