How closely do you think a planetary environment would have to resemble that of our Earth in order for life to exist there?

I never understand why we seek out only earthlike planets to look for life. Who says alien life has to look anything at all like earth life?

Life on other planets would go through completely different evolutionary processes and would presumably look completely different from what we’re used to, but it is entirely possible it could adapt to environments we consider inhospitable.

For humanity to find a new home, temperature and atmospheric pressure are negotiable; we have ways of surviving from -70F to 120F with little difficulty, and some people are acclimatized to the thin atmosphere that Earth has at 20,000 feet. Oxygen composition is less negotiable, though dependent on atmospheric pressure; a lower concentration at higher pressure yields the same amount of oxygen.

For non-human life, all bets are off. Read GURPS Space to get a good idea in an easy-to-read manner; they devote a couple of chapters to alien life, and more to planetary formation.

I don’t think anyone has ruled out planets that are not comparable to our own as possibly sustaining some sort of life, or at least having done so in the past. But finding other planets like our own probably increases the odds of a planet having life since we know that this planet does sustain life -and so far we haven’t found it elsewhere.

How about geese that can fly over 100mph at the altitude of a jet?

How does his little head not explode?

Life on Earth persists in the most inhabitable places, the coldest glaciers, the dryest deserts, acid, deep see around ‘smokers’, deep inside the earth where they literally eat rocks.
Planets do not need to be close terran conditions for life to exist.

I meant of course UNinhabitable.

^^As well as terrain…of course.

@ucme
No, I meant terran.

Silly me, you & sci-fi are never far apart…should’ve known.

Back to the question, life needs only 3 “staples” to flourish…water/things to have sex with & television, all else is purely cosmetic.

I don’t think it would have to be similar at all. Life existed on this planet way before this planet was anything like it was now. In fact the first forms of life on our planet were all about methane, there was not even any oxygen on the planet by the time it first had life.

I think however, that we should focus on planets similar to ours. Simply because it is too early in the game for humans to be predicting tricky places to find life, our best chance is probably to look for life based on us, based on what we know and can prove so far.

Here is an interesting thought…

What if the reason aliens have not visited us yet, is because they would never expect to find life on a planet covered in water and oxygen. Perhaps we are the freaks, for all we know, 99.9% of all life could start off on gas giants, or planets with poisonous atmospheres. For all we know, collagen, oxygen, carbon, and so on, could be considered illegal toxic substances by the aliens.

I understand the argument that just because life is carbon based here and depends on water here doesn’t mean that it couldn’t be something vastly different on another planet. The thing is, think about how much more complicated the search would get if we started surveying every planet we come across for life. Looking for earth-like planets is just a filter system. We know it works like that here on earth so chances are it will work like that elsewhere.

What of plasma-based life living in a star? Silicon-based life forms?

The biggest problem really is defining “life”, followed closely by recognizing life when we see it.

@poisonedantidote
Carbon is one of the most abundant and reactive elements in the universe. Hydrogen and oxygen are also at the top of the list when it comes to availability. There are more different possible molecules of carbon than there are all other elements combined. If there is life out there in the universe, it is most likely carbon based.

Planets still need similar conditions as on earth for life to begin such as water. Then for life to become complex and intellegent we need something else. Alot of luck!

@Mariah I should think it’s not only entirely possible that alien life could “look completely different from what we’re used to” and that “it could adapt to environments we consider inhospitable”, it’s highly likely that will be the case.

@jerv GURPS Space, One more book for my lengthy reading list. Thanks for the suggestion.

@DigitalBlue I don’t agree. We should examine Mars, Venus, Mercury, Jupiter and Saturn at the very least. And, for good measure, throw in the Sun for plasma based life. All are far more accessible to us than an Earthlike planet 20 light years away, which would take our fastest spacecraft over 8,000 years to reach.

@bucko Definitely amazing. But geese are amazing animals. And their little heads have evolved over billions of years so that they can accurately navigate thousands of miles and fly at high altitudes and speeds without their heads exploding. We humans may be at the top of the evolutionary tree, but if we tried to do that, our big heads would explode.

@ucme Life we know needs water. Why must all life be just as life we know? Why not liquid methane on a gas giant like Jupiter?

@poisonedantidote It is an interesting thought, isn’t it. Wouldn’t it be a hoot is sentient aliens have visited our solar system, and set up outposts on Jupiter, Saturn and Neptune, but never bothered to even examine Earth because they considered it a toxic environment unfavorable to life, all mired in water and a toxic atmosphere of corrosive oxygen as it is.

Actually, there was plenty of oxygen on Earth from its beginning, and much more arrived in the form of water carried by asteroids in the early and late bombardments. But oxygen being a highly reactive element was not in early Earth’s atmosphere. Only after plants evolved that took in CO2 and used photosynthesis to draw energy from it, and exhale free oxygen did our planet’s atmosphere begin to be hospitable to most of the life we recognize as life today.

@uberbatman Same comment I listed for @DigitalBlue above. Why is it so much easier to survey a planet it will take us 8,000 plus years to even reach than to check ones we have already sent probes to?

@jerv I would suspect that silicon based life forms are possible. If we push computer technology far enough, we may develop the first silicon based sentient life on Earth. That’s not to say silicon based life hasn’t independently developed somewhere else in the Universe already.

@Barbs666 What evidence do we have, aside from the fact that life here developed in water, to know that life cannot possibly evolve without it?

@ETpro is that not what we’re doing on Mars right now? I’m not saying we shouldnt check our neighbors but to be doing in depth studies on every planet around doesn’t seem cost or time effective, we need to somewhat filter our search until we at least know more about how life is created.

I just listened to a great NASA talk about this topic. I will see if I can find it in file format.

They went round and round in the past with the water argument, and they just think that it really comes down to the chemical combinations and the properties of the elements themselves. The believe water is thier best bet.
Good reading:
http://spacescience.arc.nasa.gov/branch/ames-center-exoplanet-studies-aces

It was a NASA google plus talk… but it hasn’t been posted. darn it. But here one to watch that looks worthwhile. http://www.youtube.com/watch?v=u5D_y9Sym1Q

@uberbatman Just saying that one filter is it takes a year or so to reach one of our inner planets to take a look, and over 8,000 years to reach the nearest known Earth-like exoplanet.

@cazzie Thanks for the links. It’s late tonight, but I will definitely listen tomorrow.

@ETpro what do you mean you don’t agree? I don’t even understand what you don’t agree with. Nowhere did I suggest that we should not explore the possibility that life can or does or may have existed in environments that we don’t typically think of as being capable of supporting life, including places within our own solar system. Are you suggesting that we should just ignore Earth like planets? To the best of my knowledge, the excitement over findings like that is simply in their existence – we won’t be venturing there any time soon. Should we just not be looking at anything beyond where we can physically go? I can’t imagine many people would suggest that we just skip over all of the parts that may be within our reach to attempt to explore something that we can’t even get to.
Personally, I’ll take all of the information we can get about what’s out there. Whether or not we ever find life anywhere else in the universe (or, hypothetically, universes.)

@ETpro http://techland.time.com/2012/09/19/nasa-actually-working-on-faster-than-light-warp-drive/

@uberbatman
And that shoots down the energy requirement argument against warp drive.
It was the same for rockets. They said that they needed so much fuel to reach escape velocity that they would become too heavy to do so. Then engineering came up with the multi stage rocket. Problem solved.

Same here. They say that the warp drive requires too much energy to operate.
Engineering solution: adjust warp field geometry.

@ragingloli yea, I’m pretty confident this is a problem we’ll be able to solve in my lifetime, at least I really hope so.

@ETPro. I am just saying it is best to start with the type of planet we already know about if we are going to find other life on planets. I am almost sure that life can develop differently on other planets in different evironments such as ours though.

@DigitalBlue My bad. Rereading your original answer, I see I read words in that were not there. You wrote planets, and I read exoplanets. Rereading what you actually wrote, I have no quarrel with it. Sorry.

@uberbatman If and when we develop warp drive, that changes the search for life equation substantially. But till we perfect such technology, I think it makes sense to search the nearby planets within the solar system. Even if we find no trace of exotic extremophile life there, we’re sure to learn a great deal about building probes capable of operating successfully in extremely hostile environments. And who knows? If we do find extremophile soaring birds flying inside Jupiter’s Great Red Spot just imagine how that redefines our notion of where advanced life might evolve.

@Barbs666 Well, Mars may have had liquid water and an atmosphere early in its existence, so we are currently exploring it to see if life developed there while conditions were more Earthlike. Other than Mars, Jupiter’s moon, Europa likely has enough oxygen-rich liquid water to support complex life. Plans are in the works to check that possibility. No Earth-like exoplanet is near enough for a probe to reach for study in a reasonable time (8,000 years is too long to wait) until warp drive or some other means of outwitting the Universal Speed COP comes along.