I have thought about this question a great deal and have decided that the meaning of human life is that we are a gigantic experiment by Nature to see if an animal capable of rational thought can survive, and I believe the jury is still out.
I say it is a gigantic experiment not because human being are so abundant, though considering our physical size, we are, but because of our ability to drive other animals and plants to extinction by various means, even live in hostile environments with the invention of clothes and discovery of fire, and have an effect on the surface temperature of the Earth. We invented agriculture to have the ability to maintain so many billions of people living on Earth. We have invented destructive items that theaten our very existence, such as the atom bomb, which is why the jury is still out.
While our ancestors have been around for about six million years, the modern form of humans only evolved about 200,000 years ago. Civilization as we know it is only about 6,000 years old, and industrialization started in the earnest only in the 1800s. While we’ve accomplished much in that short time, it also shows our responsibility as caretakers for the only planet we live on right now.*
While humans being have been around for 6 million years, sounds like a long time, there are many animals that have lived far longer: Sturgeons have been around nearly 200 m.y. (million years) (but we may drive them to extinction), Lampreys and Coelacanths have been around about 360 m.y., Horseshoe Crab has survived for 445 m.y., Jellyfish 505 m.y., and the record goes to the Sponge that has been around for 769 m.y. Yes, human beings have a long way to go to compete with animals with the longest histories.**
Also see : Global Housekeeping:The Challenge Is Issued (1990) and Is The Atmosphere An Infinite Sewer?***