Thread: Why does life need an Earth-like planet to survive?

When looking around on New Scientist and the like, scientists say that they're excited to find Earth-like planets because that means there's a chance of life being there. This makes sense of course, since life survives on Earth, so an Earth-like planet may harbour life. But I can't help but wonder if it's ONLY on planets like Earth that life can survive. For example, why couldn't a life form evolve that breathes hydrogen and methane or something like that? (That's a very crude example I know, but it gets the general idea across.) The only explanation I can think of is that if scientists thought that way, they'd have to look at every planet, which would take forever. Any other ideas?

An example of a hypothetical life form is silicon based life. It's just generally considered more likely for life to exist on similar planets.

A good summary of Hypothetical types of biochemistry is located here.

I never looked at the criteria they use, but I remember some primary factors that we can detect. That the planet is within a given range relative to the star, and that it has a moon to provide a tide. Also that it has sufficient mass to hold an atmosphere without being too massive. I don't know how fine they can do spectral analysis to determine water and atmosphere, I doubt that's good enough.

The detected planet, must be close enough to the sun for warmth, but if it's too close, it gets too hot. They might also factor in the obliquity of the planet for seasons if we can detect that.

Remember, such beliefs of discovery are still just hypothetical. Not quite to the theory stages yet where we can test the hypothesis.

I just wonder when we will uncover the startgate.

It seems to me that you could easily have an icy moon in orbit around a gas giant that could maintain oceans of liquid water thanks to tidal heating. In that case, the nature of the star etc. is pretty irrelevant. If the ocean is trapped under a few km of surface ice, the mass of the moon becomes pretty irrelevant too.

In Drake's equation, the third factor is the number of planets that can support life.
http://en.wikipedia.org/wiki/Drake_equation
The only planet that we know of that meets this requirement is the Earth. So we start by looking for Earth-like planets. However, scientists are examining many possibilities.
http://astrobiology.nasa.gov/
Bacteria exist on Earth that thrive in the radioactive cooling pools of nuclear reactors, under the ageless ice of Antarctica and in the bottom of mile deep diamond mines. Who's to say where we might find exobiology? Everything in the universe happens for a reason and self-replicating molecules must also happen for a reason that we have simply not yet discovered.

We only have a sample of one...the Earth.

As a geologist I'm less inclined to look at life today than I am at the conditions under which life first 'began' on Earth.

We can take lots of variables in which life lives today, and are still not able to 'create life'. One can boil water, add amino acids, radiation .....but no 'presto' because no life suddenly pops into being.

Life probably needs a multitude very specific variables to start. We don't know what they all are but do know they they were present on Earth a few billion years ago. Some of the necessities might be planet related....distance from a star, type of star, moons, radiation levels, atmosphere, temperature,etc.

Given a Universe with the number of stars being 10 to the 21st power. There are quintillions of planets that are similar to Earth. That's 1,000,000,000,000,000,000 or 1 Earth-like planet for every 1000 stars. It's more efficient to target these few planets knowing that life can start on a planet like earth.

Originally Posted by Darius

A good summary of Hypothetical types of biochemistry is located here.

I like the fact that the site considers the possibility of life of a completely different nature, formed out of interstellar dust.
My gut feeling is there might be many even more exotic possibilities, some of them realized somewhere in space. Perhaps on a completely different scale, with organisms the size of an atom or a gallaxy. But I don't know nearly enough physics, statistics, or chaos theory to work out such hypotheses in any detail, or to assess how probable such kinds of life are to happen.

A kind of meta-life form are memplexes. I wonder if they can evolve to a level where they exhibit purposeful behaviour of their own, unrelated to conscious or even unconscious motivations of their.... should I say hosts? Carriers?

Well I think it's because, in the way of the Milky Way galaxy, Earth is the only planet with life on it as we know.

No other Milky Way planet that we know of has life, and adaptions to the things aforementioned would have to come from the creatures of Earth. Without oxygen, they would die without chance to adapt I would think.

That's how I look at it, sorry if it doesn't make sense, I'm hardly in seventh grade.

I liked Scifor Refugee's suggestion.

The quest reminds me of our quest to find life on Mars, as if even most Earth life is on Earth's surface, head's up in atmosphere. Really, most life of Earth does not require gravity, or a surface, or an atmosphere, though those may help indirectly.

Water, plus some nutrients and radiation is good enough. Plenty of that in the universe.

Without oxygen, they would die without chance to adapt I would think.

If you walked on the street today and stumbled through a oneway time portal that lead back to the time when life began on earth, you would die very quickly.

When life began here there wasnt much free oxygen in the atmosphere and the climate was very different. Part of the oxygen from our atmosphere probably came from life that didnt breath oxygen but secreted it.

We are still unsure how life began here as far as I know and since our type of life is the only one we know of then we assume life is more likely on planets like us. For all we know Jupiter could be containing millions of tons of microorganisms in certain layers of its surface right now, but I guess if it were the case we probably would not discover it for many years to come. Microorganisms on earth appeared surprisingly soon(from a geological perspective) after the earths formation when you compare that to the time it took these first micro-organisms to evolve into more complex multi-cellular life forms.

To All

I had to go to the library because of a hacker/spammer problem.

The Egyptians selected the Sun as their Creator God RA. I beieve this was done because the Sun provides the energy for the plants to grow (probably gardeners along the river Nile).

So we need a sun. The other elements needed are Carbon, Oxygen, water, Silicon
and possibly some other trace minerals, These elements are all common in the universe because of the Consrvation Laws mandate this.
Water is common also because it is ejected from the stars during these eruptions
as a bypryduct of the hydrogen/oxygen expolsions.

Add this to the above for a hospitable environment and you have life.

Cosmo

Originally Posted by Incoming Dessert

When looking around on New Scientist and the like, scientists say that they're excited to find Earth-like planets because that means there's a chance of life being there. This makes sense of course, since life survives on Earth, so an Earth-like planet may harbour life. But I can't help but wonder if it's ONLY on planets like Earth that life can survive. For example, why couldn't a life form evolve that breathes hydrogen and methane or something like that? (That's a very crude example I know, but it gets the general idea across.) The only explanation I can think of is that if scientists thought that way, they'd have to look at every planet, which would take forever. Any other ideas?

I really think it's quite possible(if not likely) for there to be life competely different than our own. The thing is scientist go off what we know can support life. Like you said it would be vitualy impossible to try and find every possible planet with a possiblity for life. We KNOW earth like environments can support life so thats what we look for. The rest is just speculation.

Originally Posted by Incoming Dessert

When looking around on New Scientist and the like, scientists say that they're excited to find Earth-like planets because that means there's a chance of life being there. This makes sense of course, since life survives on Earth, so an Earth-like planet may harbour life. But I can't help but wonder if it's ONLY on planets like Earth that life can survive. For example, why couldn't a life form evolve that breathes hydrogen and methane or something like that? (That's a very crude example I know, but it gets the general idea across.) The only explanation I can think of is that if scientists thought that way, they'd have to look at every planet, which would take forever. Any other ideas?

I guess the main reason is that you wouldn't get any funding for exotic ideas. It is not even clear that there is life on other planets than earth. So, why should any funding agency raise any money for a project, where the outcome is very likely close to zero? So, they are concentrating on configurations, where the the probability for success is at least a little bit higher.

I personally also belive that restricting oneself to life forms similar to what we know from earth is very narrow minded. I could also imagine that it is very possible that we would not even recognise exotic versions of life if we saw it. For example: Why shouldn't crystals of a certain kind be capable of forming something that we could call life? Crystals can store energy and information. The can even form large combined entities. Growth is also possible, similar to what we know of bacteria.

Besides, I think that the famous Drake formula does not say anything. You just multiply a lot of probabilities, where each of them has a large uncertainty. So the result can be anything you like. I would not use it. And the global ideas about distance of planets from the central star - the habitable zone - is also nonsense, because the temperature at the surface of such a planet is either insignificant for the sustainability of life (see various exotic species on earth), or the real temperature depends on weather phenomena like atmospheric pressure and gas abundances (see Venus, Earth, Mars). I think that at the end of the day, this is just another symptom of the old global human delusion that we are something divine and special in the vast universe.

Originally Posted by Dishmaster

restricting oneself to life forms similar to what we know from earth is very narrow minded.

Yes, but it is practical. A krill fishery on Europa is gonna pay off better than a slow chat with smart mist of the Oort Cloud.

Originally Posted by Leszek Luchowski

Originally Posted by Darius

A good summary of Hypothetical types of biochemistry is located here.

I like the fact that the site considers the possibility of life of a completely different nature, formed out of interstellar dust.
My gut feeling is there might be many even more exotic possibilities, some of them realized somewhere in space. Perhaps on a completely different scale, with organisms the size of an atom or a gallaxy. But I don't know nearly enough physics, statistics, or chaos theory to work out such hypotheses in any detail, or to assess how probable such kinds of life are to happen.

A kind of meta-life form are memplexes. I wonder if they can evolve to a level where they exhibit purposeful behaviour of their own, unrelated to conscious or even unconscious motivations of their.... should I say hosts? Carriers?

Memeplexes! A good book on that is "The Meme Machine" by Susan Blackmore. If artificial intelligence is ever created or memes become somehow sentient, they won't need their current hosts (us, PCs, the internet), so they won't require any habitable environment by our current standards. So at least intelligent life, given some time, would not necessarily have to be sought on habitable planets.

When we look out into the galaxy, we interpret everything in terms of ourselves. We assume exoplanets must be earthlike in order to harbor life. This may or may not be true.

Originally Posted by Incoming Dessert

When looking around on New Scientist and the like, scientists say that they're excited to find Earth-like planets because that means there's a chance of life being there. This makes sense of course, since life survives on Earth, so an Earth-like planet may harbour life. But I can't help but wonder if it's ONLY on planets like Earth that life can survive. For example, why couldn't a life form evolve that breathes hydrogen and methane or something like that? (That's a very crude example I know, but it gets the general idea across.) The only explanation I can think of is that if scientists thought that way, they'd have to look at every planet, which would take forever. Any other ideas?

GFAJ-1 Link

I think many scientist have just flat out given up on finding life beyond earth and have pushed the idea way down the expectation road and further into the realm of science fiction.

Life, theoretically, does not need earth or an earth like planet to form. Either life is abundant throughout the universe, or it is not IMO.

Originally Posted by gonzales56

Originally Posted by Incoming Dessert

When looking around on New Scientist and the like, scientists say that they're excited to find Earth-like planets because that means there's a chance of life being there. This makes sense of course, since life survives on Earth, so an Earth-like planet may harbour life. But I can't help but wonder if it's ONLY on planets like Earth that life can survive. For example, why couldn't a life form evolve that breathes hydrogen and methane or something like that? (That's a very crude example I know, but it gets the general idea across.) The only explanation I can think of is that if scientists thought that way, they'd have to look at every planet, which would take forever. Any other ideas?

GFAJ-1 Link

I think many scientist have just flat out given up on finding life beyond earth and have pushed the idea way down the expectation road and further into the realm of science fiction.

Life, theoretically, does not need earth or an earth like planet to form. Either life is abundant throughout the universe, or it is not IMO.

Good point.
Some scientists speculate on whether there could even be life on the surface of stars. Magnetic aliens might seem a bit far fetched but it might be plausible though; if there's a means of codifying information and some sort of organised complexity in a given environment then life could turn up on/in the most unexpected places.

Rather than asking why life has, so far, only been found on Earth, I think better questions to ask are: Why isn't life found on any other planets? Why isn't life abundant throughout the observable universe? Raptordigits gave a good example by pointing out the variables needed for intelligent life to evolve.

In our own Solar System we find different conditions on each of our Planets. All for the right reasons of course. And thats in our own backyard. Now we have a look at our Galaxy. The milky Way Galaxy. If we cannot have two of our Planets in our Solar System with identical invironments, the odds in our Galaxy having the same invironment as Planet Earth must be fairly long. Having said that there must be Planets in our Galaxy with a great variety of invironments, unknown to us or our Scientific Principles. Or Physics. Or Chemicals. Never say never. There may even be a Laughing Gas Planet out there, atmosphere 100% Laughing Gas. Wouldn't it be fun to go there. westwind.

Originally Posted by Jim Colyer

When we look out into the galaxy, we interpret everything in terms of ourselves. We assume exoplanets must be earthlike in order to harbor life. This may or may not be true.

I think it is more the question of the drunk and the car keys. The drunk looks for his car keys under the street light, not because he thinks thats where he droppped them, but because that's the easiest place to look.

Originally Posted by gonzales56

I think many scientist have just flat out given up on finding life beyond earth and have pushed the idea way down the expectation road and further into the realm of science fiction.

Over the last few decades exobiology has been one of the fastest growing branches of science around. What evidence do you have that the reverse is true?

Originally Posted by jgoti

Some scientists speculate on whether there could even be life on the surface of stars

I've seen such speculation in science fiction, but do you have any links to serious suggestions by bona fide scientists?

Incoming Dessert,

......I can't help but wonder if it's ONLY on planets like Earth that life can survive. For example, why couldn't a life form evolve that breathes hydrogen and methane or something like that?......

The late Carl Sagan's book Cosmos contained all kinds of speculation concerning what he thought to be the many different possibilities of life. It's also full of very interesting colored conceptual ideas. You might pick up a copy at the library and check it out. Carbon based life like ours seems the most likely form of life because carbon seems to more easily form long chemical chains than any other element. I think silica is thought to be the second best possibility. Accordingly there are a great many possibilities of alien life but the Earth is the only model of life that we know of, so our monies in the foreseeable future will be spent looking for other carbon based Earth-like life. Such possible discoveries in the foreseeable future will be in such places as Mars, the under-surface oceans of at least two Jovian moons, Titan, and maybe within other gas-giant moons.

I'm sure you meant silicon (an element) rather than silica (a compound)

Originally Posted by MeteorWayne

I'm sure you meant silicon (an element) rather than silica (a compound)

Yes, such silicon chemistry would certainly include more compounding elements than just oxygen as in sand-based life -- SiO₂

This is simply an assumption formed by our knowledge of Earth's living organisms. For now we must simply assume we our correct because we have no way to test the living conditions of organisms which could be dramatically different from any life on Earth.

This is simply an assumption formed by our knowledge of Earth's living organisms

And somewhat dated information. Habitability zones were before biologist found deep water hydrothermal vents which wouldn't require surface water. During our snowball phase, Earth had life, but from afar would appear to be a inhospitable place far too cold to support our current notions of habitable.

argg....this is a necro thread.

Yes, a necro thread, but the neo conversation's been pretty good!

Originally Posted by John Galt

Originally Posted by Jim Colyer

When we look out into the galaxy, we interpret everything in terms of ourselves. We assume exoplanets must be earthlike in order to harbor life. This may or may not be true.

I think it is more the question of the drunk and the car keys. The drunk looks for his car keys under the street light, not because he thinks thats where he droppped them, but because that's the easiest place to look.

Originally Posted by gonzales56

I think many scientist have just flat out given up on finding life beyond earth and have pushed the idea way down the expectation road and further into the realm of science fiction.

Over the last few decades exobiology has been one of the fastest growing branches of science around. What evidence do you have that the reverse is true?

Originally Posted by jgoti

Some scientists speculate on whether there could even be life on the surface of stars

I've seen such speculation in science fiction, but do you have any links to serious suggestions by bona fide scientists?

when one goes from looking at the moon, mars, venus, gas planet moons, neo's then they cut nasa, start speculating about possible life on earth like planets well beyond the reach of humans, then the shift from discovery and exploration to speculation and fiction seems apparent IMO.