Why is earth the only planet with lifeforms?
141516
The only planet we know of that has life is earth. Based on that very limited knowledge we can only estimate that earthlike life forms would have had great difficulty evolving in the worlds, in and out of the solarsystem, that we know of today (new planets are discovered almost daily). It is probably possible for terrestrial organisms to survive and maybe even prosper if introduced to some shielded and protected water rich enironments on the other worlds described above but there is a great difference between merely surviving and evolving. Life requires very special environments and conditions for a very long period of time, hundreds of millions of years, to evolve. We cant say for sure that those conditions were ever present on any world other than earth. But once life is born on a world it is extremely hard to extinguish completely as it would constantly evolve to adapt to changing environments. Life has nearly ended on earth many times as environments changed but has always bounced back. So if there was life on any other world in our solarsystem it would be so plentiful by now that we would have found traces of it in their atmospheres or in their soils. But we havent.
226998
I think so.  Given the probable number of other planets (nearly infinite), it defies logic to think that Earth is the *only* place in the universe that life developed.\n\nI have not had any contact with extraterrestrials myself, however, so I am not speaking from personal experience.\n\nEdit 3/16\nAfter posting my answer, I watched a show on the History Channel about Meteors.  One of the things the show presented was a meteorite that is believed to have come from Mars and *may* have signs of fossils embedded in the rock, fossils of living organisms -- bacteria.  The meteor is called ALH 84001.  Here is a website about it:\n\nhttp://www.lpi.usra.edu/lpi/meteorites/life.html
408320
Very niave!  We have been shown that there are other living organisms on other planets that we have have snet out to study.  Just because they are not in human or (our) peoples form does not mean that the planet is not alive. We have also been shown to where some planets have shown previous life on them.
1132699
Well.. \nI'm more scientific than religious in this matter. \nThe reason Earth has life is because of the certain climate, temperature, etc. which is perfect for life. \nHowever, there are always news stories about "possible life on mars" and as such. And I believe that for life to form, there needs to be a certain set conditions which allow life to be formed and which support and maintain it. \n\nTherefore,  most definitely there could have been life in other planets, maybe some organisms or something else which is suited to that planet's climate, temp. and etc. It could be that we either can not detect that life on the other planets or the planet is undergoing some sort of climatic change which does not support life due to variant pressures. \n\nDid god stop at Earth-- well, that is a question which is a matter of belief- if we consider god as a positive force which stimulates life- then no, god wouldn't have stopped only on Earth. \n\nSome research even claims that there are other solar systems with other stars (like our Sun) in which a planet is very like Earth- almost same which supports life. \n\nSo, whether life is or not- is a personal decision. I think there is- but as you say, there is no real solid evidence supporting or contradicting existence of life in other planets
199746
having life only exist on earth is like picking up a single grain of sand and saying that that grain was the most perfect grain in the entire world...it would be impossible to know this unless every other grain was examined, and the fact the new grains are constantly being made.  there are over 200 billion galaxies in the visible universe and a couple hundred billion more out there, all containing stars and planets that maybe able to sustain life.  and by "life" that also takes into account of any micro-organisms like bacteria and viruses and any other forms of life that might exist.  So to say that there is no life on other planets would be incorrect to assume, it's just a matter of time in trying to find it, whether it exists in our solar system is still debatable as micro-organisms can live in harsher conditions that larger organisms arent able to
508538
life on other planet would not mean they should be all humans. don't forget on our little planet there are 1000s of different living creatures, they are not all human. therefor there might be life on other planets in different shapes and different creatures, that would not mean there was some other God who created them.\nThe Bible says god created the heavens and earth. it doesn't say if God created or didn't create any creature elsewhere.\nthe bible was sent to us earthly human to learn about God and how to worship Him. There was no point to intriduce other worlds to the ancient humans because of their lack of understanding.\nour understanding of how to interpret the bible changes through time and history.\nThe early church thought of science as anti-religion. and they thought the earth is the center of the universe, even though the bible doesn't say that, it was implied that God will create the earth and give it so much attention only to make it the center of everything. But as we learn more things about the universe we read the bible and see there is nothing in the bible that contradict it. so if one day we discovered life some other place, there is nothing in the bible that says that should or could not happen. it is only our understanding now that assumes God created only living creatues on earth..
778934
Well, the Earth is the only planet with a magnet field in our star system. The reason is because we have a liquid core and a solid surface. Other planets are either solid (like Mars) or gassy (like Jupiter and Saturn)
18963
This is a little hard to answer.\n\nFirst, we haven't found any.  So there's no positive evidence, so it's hard to be really sure. \n\nBut on the other hand, there are billions and billions of planets like ours, and it would be really weird if ours was the only one to have life on it.\n\nSo most astronomers think there's probably life out there somewhere.  I hope we find it.
234001
This is a tough question...\nIf you mean life as we humans know it then the number is pretty small. - For life we need air,water,warmth and gravity.\nWe need to be near a sun - have oceans and land - the correct rotational axis to promote changes in seasons and lastly, a moon to create the tides.\n\nBut if you mean life as a whole... \nThen any planet that can support it would indeed have it.\nThese are a much larger group. We have even seen existance of life on Mars (microscopic bacteria).\n\nMy belief is that there is more than one Earth like planet ou there. We may even see it someday.\nWe have believed that they would seek us out - I believe we will seek THEM out.
503194
There is a possibility of other living matter existing other than the humans.There are billions of stars and there may be many more earth's around them.When the conditions of existance of life prevails ,like for earth -water,atmosphere,essential gases and many more exist.Ofcouse there may be different conditions in other galaxies but there is a possibility that life exists.Them being friendly or visious depends upon the way we try to communicate with them.If the way we communicate is wrong they may prove to be more visious than friendly.
438713
your right. i also believe that life on another planet dosent need to have water present to sustain life.\n\nits just that they are trying to find life on other planets and if they find water there is a chance that there was or is life on other planets.
386417
Every being on earth's appearance is determined by their lifestyle/environment/etc, up to a point, and I wouldn't expect anything else for life forms of other planets.\n\nAre we talking about other carbon-based life forms, or are they methane-basted? Or ethane-based? Or, why not, even hydrogen-based? What kind of environment do they live in? What type of atmosphere does their planet have? What is the climate?\n\nAsking what an alien like is sort of like asking what an animal looks like. I bet there are so many different types...\n\nOne failing of a lot of science fiction is that, in the designing of the aliens, they just wanted to make them as weird a version of humans as possible, without thinking about what sort of biology their home planet would naturally produce.
320654
Scientifically, since life evolved on earth it has to occur somewhere else in the universe because of the sheer number of stars and planets out there.  Most astrobiologists will actually concede that life is fairly common in the universe, but the main argument is about intelligent life.  Since we don't know enough about the evolution from single-cell organisms to intelligent life, we really have no idea if we're being visited by little green men.
244698
Because it is enormously incredible that in a universe made up of billions of stars, we are the only "intelligent" life that the universe has developed over millions and millions of years. The only thing more exciting than finding fellow intelligent ctreatures in the universe would be for them to find us.\n\nWe know that evolution on this planet was interrupted several times by earth-shattering events. What if those events did not happen on another planet in another galaxy (yes, even one)? How much further evolved and developed would they be? And if that other planet did not have the dead end dinosaurs turned out to be? Millions of years and no sign of intelligence. It took giving a little shrew-like creature a chance to evolve to get to us.\n\nHumans have gotten where we are because of curiosity, a need to find out why things happen and what is happening. Societies that stifle curiosity are the backward ones, destined to be lost in history.
185479
It would be very arrogant to think that this would be the only planet in the whole universe where any sort of life has developed.  There are so many stars and planets in the universe that even if only a fraction of a percentage were capable of supporting life as we know it, and only a small number of them developed "intelligent" life forms, there would still be billions of alien species.
605325
the Earth 3rd planet from the sun; the only planet were life exists; the Earth moves around the sun.\n\nto know more about the earth or the astronomy and space contact me :)
663417
ok well think about this: ours is the only planet we know of that has liquid water on the surface. others have no water or the water is frozen. If there were life on every single planet that has liquid water on the surface, we still would not yet have discovered extraterrestial life.