What are the chances that only Earth has life?
549644
A bunch of experts (astronomers, biologists, etc.) once met to answer your question in Greenbank, West Virginia in the 1960s.  They only concerned themselves with life in the Milky Way.  They developed a formula, sometimes called the "Drake Equation".  Depending on the numbers you place in the seven variables of the equation, you can come up with answers that range from "a million" down to "one" as the answer.
1133600
Yes. There has to be! In the trillions of stars and billions of planets, by virtue of the odds, there has to be. Will we be able to find life? Very doubtful.
261850
Statistically, it is very hard to believe that we (Earthliens) are along in the universe, there must be something else out there.\nAt the same time, the odds that life would develop independently on both Earth and Mars in the same solar system is pretty slim (unless life is actually not nearly as rare as we might think).\n\nThere is of course a chance that life may have developed on Mars in the past when the conditions were more suitable, but so far, we havent found anything.  Although there is the possibility, I am leaning towards no.\n\nBut think what that would mean if we discovered life outside of Earth (especially on Mars), it would be the most important discovery...ever.  If life can develop independently on two planets in the same solar system, either we are very lucky, or it the whole universe must be crawling with life (or you could throw the God factor in if you wish).
1071064
Absolutely not and I think it would be incredibly arrogant of us to think we are the only life in the entire universe, considering how many billions of planets, if not galaxies, there are.  There are more that can sustain life.
1089400
It seems very possible that asteroids seeded this planet with life. That might have not been as accidental as some people think.
160820
most probably.. life of other planets is probably totally different from that of our planet.. but it definatly exists
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
888149
If Earth suppports life, the least you can do is support the earth!\n\nEarth the supporter of LIFE ... LIFE the supporter of YOU!
362430
I think we would be very naive to believe we are the only life form in the universe.As vast and diverse as it is,I believe there has to be a reason for the formation of these planets to sustain life.That said,who knows when the life was present on these planets?And who knows what life forms are out there as we speak?Perhaps Mars and Pluto had life trillions of years ago but there are no remnants now for us to find.It's a fascinating topic.If you think about the possibilities,it's incredible.
356504
Yes, the Bible says God put life on Earth and no where else.  Therefore there are no UFO's or life of any kind on any other planets.
671308
Of course I think life exists!  Infact, I beleive there is life in the solar system.  How do we know if there isnt life floating in the clouds of a gas giant, or icy crystal like things on pluito?  We havent searched hard enough for these yet!  Duh!\n\nLife outside of the solar system might be a little hard, considering that there are only "hold jupiturs," and "frozen earths."  Both are to hot or cold to support life, and they are massive and have insane gravity.  However certain single celled organisms, say bacteria or such, might reside on the planet.  I always thought that might be.\n\nIn addition, Europa, a moon of Jupitur, has ice flows on it that scientists think liquid water might reside under!  It might be interesting to see what could live there.  From the means of life there, I came up with a skating green creature who could move around on the ice, absorb the moisutre of the water, and undergo photosynthesis to obtain energy.  \n\nEnjoy!\n\nNote: I do beleive in aliens, but dont beleive in UFOs.  Considering how many hot jupiturs there are, I dont think we will even see any life as smart as we were as cavemen until alot later in time...
22092
How can we be alone?\n6,487,053,332 humans moving on the planet (http://www.census.gov/main/www/popclock.html) and u say we are alone!!!\nJokes apart... there is enough probability for life to exist in the universe.... if we are existing here... then there can be some other organism existing elsewhere...\n\nDefinitely there is life elsewhere... only problem... it'll take time to find them out...
299526
As far as we know, Earth life specifically uses only one chirality, and in fact this is one reason we may not be able to live on other planets that have life (science fiction premise).  If you have found a life-form, then that would be one way.  A more direct way would be to partially sequence the DNA, to determine if there are shared genes (all life shares some genes, from human to bacteria, that shows the evolutionary relationship).  You might also examine the cells to determine if the intracellular organelles are normal (presence of mitochondria, etc), and sequence the tRNA-transfer RNA in eukaryotes (multi-cellular cells) is all very similar, and that of prokaryotes is similar.  Also, run an analysis of the amino acids- Earth life uses a small minority of the types of amino acids that are possible-presumably alien life would use at least some different ones.
13800
The problem with your question is that assumes that there are only to possibilities; we're alone, or there are little green men walking around.  \n\nChances are that there is some form of life other than ours in the universe, but it more than likely will be much more different than just having different skin and being a different size.  Think about how weird all the animals at the bottom of the ocean.  Then think about how similar their need for water, oxygen, food, how similar their DNA is to ours.\n\nNow try to imagine life evolving on world rich in totally different elements, exposed to total different frequencies and concentrations of energy.  The thing about life on other planets isn't really whether or not it's out there, but whether or not we'd even be able to recognize it when we see it.  \n\nThat and the fact that it takes years just to move from one solar system to the next.  Just getting to another planet capable of supporting life would more than likely take decades, even centuries with any conceivable technology(though an alien lifespan could make that less significant).  Any alien capable of travelling that distance, whether by nature or technology, would once again likely be so different from us that we would never recognize one another as living beings.  So there you go, little green men, probably not, alone in the universe, who can say.
728914
We don't know for sure, but probably there is.  \n\nScientifically, think about it.  If there is a .001% (a random low number) chance of life living in a solar system, and .001% chance of life on a planet in the solar system, and a .001% chance of the life being intelligent, the chances are really good.\n\nIf the universe is unlimited in size, then then these figures will mount up and eventually the probably will get to 100% that intellegent life exists somewhere.  \n\nLet me clearify: you can say that if a galaxy has 10 planets and there is a .001% chance of life existing in that one galaxy, there's a .01% chance of life existing there.  However, the universe (as far as we know) is unlimited in size.  There is an unlimited amount of planets in the universe, therefore, you can speculate that there is a 100% chance of life existing in outer space (because there are unlimited number of planets).  I think that I clearified it, if not let me know.  ownager@sbcglobal.net
611976
Definitely.  Even if its just some microbes out in space, just the sheer number of planets and stars etc I would think there would have to be other life out there!
1184402
Yes, we will discover other planets that also sustain life, and we will do so within our lifetime.  I do not mean that we will physically go to these planets but we will discover this by placing much more powerful telescopes in orbit around Earth.  There is a definite signature that we will be looking for and that will be the presence of Oxygen in another planet's atmosphere.  If a planet does not have any oxygen in its atmosphere then it would not be able to support life.  There was a time billions of years ago on Earth when there was no oxygen in the atmosphere and at that time there was no life on Earth.  We may not discover other intelligent life on other planet's during our lifetime but i am sure that we will discover other planets that are supporting at least plant life if not primordial single cell life as well.