life before us?

[claymore]

How long after the beginning of the universe would it have taken for the first signs of life to appear? What I mean is when was it stable enough for life to begin? If you subscribe to the belief that life is spread throughout the universe, could great civilizations have risen and disappeared long before our solar system came into being .

[wildwood]

About 10 billion years, give or take a couple of hours.

So far there is no solid evidence that life evolved anywhere other than on Earth. When you mention 'civilizations' you assume that if life is(was) present somewhere else in the Universe, it is in the form of humans. This is somewhat of an misguided perception of evolution. Life on Earth has progressed nicely without humans for billions of years and now that we have arrived in a twinkle of an evolutionary moment, we will destroy most of the lifeforms if not the whole planet.

It is remotely possible that life is/has been somewhere else but just because it is possible doesn't mean it is/has.

[jake-the-peg]

Well the first thing you need is heavy elements. Everything heavier than Helium was created in the first generation of ( cunfusingly named population II ) stars. These have to run the course of their lives before they can explode and seed the area with heavier elements.

The sun is one such second generation star and that is about 4 billion years old and the Universe is probably about three times as old. But the first generation stars may well have been much more massive and longer lived .

So I guess it depends on how much earlier you are looking for these civilisations.

If you're talking about hundreds of thousands of years earlier then there was definately a window where they could have existed on Earth (but we're pretty sure they didn't) so they definately could have existed elsewhere.

Similarly if you're talking billions of years then probably not, but I don't see why they couldn't have existed in the middle.

It would be somewhat arrogant to assume that our planet won the "race" to produce an intelligent life form.

[beso]

Slight correction to Jake's post. Bigger stars have shorter lives.