Vast assemblages of molecular gas with masses of 104–106 times the mass of the sun are called Giant molecular clouds (GMC). The clouds can reach tens of parsecs in diameter and have an average density of 10²–10³ particles per cubic centimetre (the average density in the solar vicinity is one particle per cubic centimetre).
GMCs are so large that "local" ones can cover a significant fraction of a constellation such that they are often referred to by the name of that constellation, e.g. the Orion Molecular Cloud (OMC) or the Taurus Molecular Cloud (TMC). These local GMCs are arrayed in a ring in the neighborhood of the sun coinciding with the Gould Belt. The most massive collection of molecular clouds in the galaxy, the Sagittarius B2 complex, forms a ring around the galactic centre at a radius of 120 parsec. The Sagittarius region is chemically rich and is often used as an exemplar by astronomers searching for new molecules in interstellar space.
Having established that these clouds are big, and don't create single stars, we can assume then that, it would be strange to find things were not extremely similar. Couple this with the idea of panspermia, which has been brought up several times recently by very rational and intelligent people, and you have an interesting possibility.
ATS Post on recent news & Another news source on a different perspective of panspermia.
This possibility is that, within the same nursery that created our sun, the building blocks of life were also formed. So, you have the possibility that basic life is created externally and eventually rains down on a forming planet like the rest of the matter. If this is the case, which it appears there may be reason to believe it is, than we should assume that planets, formed from the same basic building blocks (essentially H2), as life. That being said, if another planet in our vicinity was seeded, and life successfully took root, it would be subject to evolution similar in nature to earth.
Even on earth we have examples of convergent evolution. Where several different species will find different means to the same end, for instance, flight. So, one could assume that, if another conscious lifeform arose, and it was near enough to us to have visited, we may well find that this life is very much like us. Subject to the same requirements for sentience as us. Probably bipedal in order to elevate the brain, standing upright to avoid overheating, with limbs and sense organs etc. Not to say that biologically they wouldn't have taken a very different route. It is highly unlikely we will find any planets that are EXACTLY like earth.
This however should not discourage the possibility of nearby life, as we have life in the darkest coldest most inhospitable places of the planet. The trouble life has is starting, it can survive just fine. If the new insight into panspermia theory proves correct, and we truly are descendant from microbes carried by comets, than we most certainly weren't the only planet lucky enough to be seeded. The comet was part of a certainly larger cluster, perhaps the same cluster that brought our water.
Nonetheless, at least in my opinion, we cannot rule out the fact there is the possibility for earth-like life of all types to exist near us, and that life further away, formed from different GMC's would yield different results.
Post continued below...
[edit on 6-2-2010 by JunoJive]
