If civilizations exist around other stars they are likely to be just emerging across our galaxy right now, says Space Telescope Science Institute astronomer Mario Livio.

Before the universe could make life like us it had to make carbon atoms, the fundamental chemical building block of life as we know it. Carbon was created by nuclear fusion in the hearts of the universe's first stars, then ejected when the stars lost their outer gas layers. Based in part on Hubble Space Telescope observations, Livio calculates that carbon production in the universe may have peaked only two billion years before the Sun and Earth formed.

Though simple life forms appeared on Earth nearly 4 billion years ago, it's curious that intelligent life didn't appear until our Sun was halfway through its 10 billion-year lifetime, adds Livio. He believes the reason is that, because sunlight provides far more energy for life than other chemical processes, biological evolution is intimately linked to the Sun's behavior. For example, the complex evolution of our atmosphere is interrelated with the Sun. Our planet's atmosphere had to develop ozone to block out destructive ultraviolet radiation from the Sun before animals could emerge onto the land and then evolve into a species that could develop a technological civilization.

Based on these conclusions the very oldest civilization in the universe would be no more than 3 billion years old. Of course, that is an enormous stretch of evolutionary time. A civilization that far ahead of humans might find us as uninteresting as an amoeba is to us!