ukmicky said:
what I'm trying to find out is if life was something that was inevitable and theirfore happened more than once or if it was just a matter of extreem luck and only happened once, which would then have a major bearing on the chances of us finding extra terrestrial life.
This is arguably one of the most important questions facing science today, and like all good questions it has no clear answer.
I would recommend to you a book called
Rare Earth, by Ward and Brownlee. They examine the likelihood of life beyond the Earth. Their conclusion is that microbial life is common in the Universe, but that intelligent life is very rare, possibly even unique.
We have seen that life can exist in a variety of hostile environments, which a few decades ago we would have thought would have excluded life. So we now have the various extremophiles inhabiting very cold, or very hot, or very saline, or very acid environments. When Apollo astronauts recovered parts from one of the robotic Surveyor spacecraft from the moon, it was found that some microbes left on the craft accidentally were still viable.
This gives us a very wide range of habitats in the Universe in which life might arise and flourish. However, for complex multi-celled organisms capable of developing intelligence to emerge and survive, appears to be a much more challenging task, with a much more restricted range of opportunities.
One of the puzzles concerning the origin of life is how quickly it appeared on the Earth. The Heavy Bombardment Phase, that peppered the Earth and all the terrestrial planets with comets and asteroids, occurred 3.9 billion years. We have clear fossil evidence from 3.6 billion years ago. So it seems that life emerged in just 300 million years.
Now that seems like a long time, but consider this. The prokaryotes, microbial life forms without a nucleus, had the planet to themselves for one or one and a half billion years. They are often referred to as primitive, yet the difference between them and non-life is far greater than the difference between them and the eukaryotes (which include all the multi-celled plants and animals). So it appears as if this transition to life occurred rapidly, in comparison with the transition to complex life. That raises questions.
It may be that we shall discover self organising properties of organic compounds that lead inevitably to life. In that case we would expect that there may have been several forms of life which emerged at the outset, only one of which was ultimately successful. It is unlikely that we would be able to capture the signature of that life form. An alternative explantion would be that life arrived here from space on comets. This is an old idea that has enjoyed something of a resurgence of late: google for
pan spermia.
