Does life here on Earth indicate life elsewhere?

  • #1
Loren Booda
3,119
4
What does the presence of life on Earth imply about the chance of life existing on other worlds?

Can one assume, with high probability, that despite Earth's seeming singularity of life, there is life elsewhere in our (assumed finite) universe? In our (assumed infinite) universe?

A possible definition of life would be entities that reproduce nucleic acid through assimilating their chemical environment.
 

Answers and Replies

  • #2
lzkelley
277
2
Good question; I'll start with the details: the universe is definitely finite. Also, one can't really say Earth seems to be the only location with life, as life on other planets necessarily wouldn't have been discovered unless they came by (which is practically impossible even theoretically, not to mention statistically).

As for your actual question: with the discovery of many near Earth mass extrasolar planets close to and in the habitable region of their solar systems, it seems very probable that there exists other life - in respect to planetary requirements. Based on our current knowledge, there is no reason to think that life would be unique to earth, although it is certainly difficult to form.
 
  • #3
mgb_phys
Science Advisor
Homework Helper
7,889
15
What does the presence of life on Earth imply about the chance of life existing on other worlds?
The discovery that fairly complex life appeared on Earth within 100Myr of it cooling and it's existence in such extreme conditions as deep sea vents and deep in crust rocks suggests that life appears where ever it is energetically possible and so might be a lot more common than once thought.
 
  • #4
Dark Fire
40
0
the universe is definitely finite.

Strong words.
Based on where science & physics is so far, is the universe finite: yet travels by the speed of light, that may possibly not be exceeded, which is therefor in an infinite speed in comparison with reach.

@Topic, I honestly got no strong opinion about this, except: that I find our life (all creatures on Earth) not as anything close to a proof or fact of other existence, yet very possible and hopefully yes.
 
  • #5
Kenny_L
127
0
Good question; I'll start with the details: the universe is definitely finite.

You don't really know this for sure. You don't know if the universe if either finite or infinite. Also, nobody yet knows if there is life elsewhere. It is definitely 'possible', because one can just assume that if life is here, then there could be living things elsewhere. But, we don't have any information. Like, for all we know, we could even be the first (or only) ones living. You just never know. On the other hand, there could be heaps of other living things out there. We don't know that either.
 
  • #6
baywax
Gold Member
2,157
1
What does the presence of life on Earth imply about the chance of life existing on other worlds?

It implies that life does exist in other sun systems. The stage of life's development may not match ours or may be of a completely different evolution. However... when we see that we have a sun and every other system has a sun... and we see that every other system has planets like our own... and we see that all the other conditions found in our solar system exist in other systems throughout the the galaxies and clusters of galaxies... then we can assume that life is a component of some of these systems as it is a part of ours.
 
Last edited:
  • #7
Adeimantus
113
1
What does the presence of life on Earth imply about the chance of life existing on other worlds?

Can one assume, with high probability, that despite Earth's seeming singularity of life, there is life elsewhere in our (assumed finite) universe? In our (assumed infinite) universe?

How about this...

h = the proposition that life is fairly common in the universe (it occurs in a non-negligible fraction of the solar systems)

e = event that life is observed on earth.

Plug these into the Bayes formula

P(h|e) = P(e|h)P(h)/P(e)

where P(e) = P(e|h)P(h) + P(e|~h)P(~h)

From the definition of h, P(e|~h) << P(e|h), so if you started out relatively indifferent to the hypotheses h and ~h (ignoring for the moment that you know there is life on earth), the above equation for P(e) becomes

P(e) is slightly greater than P(e|h)P(h) or

P(e|h)/P(e) slightly less than 1/P(h).

Plugging this into Bayes' formula gives

P(h|e) is slightly less than 1.

Of course, this depends on you being relatively indifferent to the propositions h and ~h, which may not be the case. If you assign P(h) << P(~h), then you can't neglect the second term in the equation for P(e).

P.S. After thinking about it some more, I'm pretty sure there's a serious flaw in the above argument, but I'll see what others think...
 
  • #8
DaveC426913
Gold Member
21,363
4,823
A possible definition of life would be entities that reproduce nucleic acid through assimilating their chemical environment.
Why so limiting?
 
  • #9
Loren Booda
3,119
4
Just "possible," it errs on the side of doubtfulness. In retrospect, it is too limiting.
 
  • #10
baywax
Gold Member
2,157
1
Just "possible," it errs on the side of doubtfulness. In retrospect, it is too limiting.

I've heard that crystals are reproductive in some way or another. I thought this was only when they're under pressure but people say the continue to grow once they're out of the ground.

There may be some type of life form arising from that but we do not see it here. Crystals have proven to be very useful in terms of storing data and transmitting info... they are also part and parcel to the encapsulation of viral RNA. Perhaps there is the possibility of a more evolved form of crystal with free-associative powers, logic and what we'd call "intelligence" lurking in the neither regions of the "old" universe.
 
  • #11
K.J.Healey
622
0
I don't think its a safe assumption. In reality Earth is a small sample size.
Because my left hand looks the way it does, and there's 6+ billion other people in the world, does that mean someone else has the exact same left hand? What if it were a billion billion? Its not answerable.
You would have to look at the number of configurations/pieces it takes to make this hand unique. Then you have a gauge of the statistics.
For life, until we create it in the lab, we're not sure how many molecules have to be this way with this much energy and blah blah blah, and we have no idea the probability of its occurrence. Nor do we know how many different configurations can be used to make "life".
 
  • #12
Kenny_L
127
0
It implies that life does exist in other sun systems.

I think you're close...but the word 'does' should be 'could'.
 
  • #13
baywax
Gold Member
2,157
1
I think you're close...but the word 'does' should be 'could'.

I think you have to include time in the equation that explores whether or not life on Earth indicates life occurring elsewhere.

So much time has gone by since the theoretical BB that life could have developed and evolved to incredible complexities then completely destroyed by one factor or another.

I'm not sure if this makes it more probable or less probable that life has or is occurring elsewhere as it is today on earth.
 
  • #14
Kenny_L
127
0
So much time has gone by since the theoretical BB that life *could* have developed and evolved to incredible complexities then completely destroyed by one factor or another.

That's right. I agree that life *could* have developed elsewhere. We don't know if it 'did' develop elsewhere.
 
  • #15
N468989
92
0
Life on Earth doesn't indicate life elsewhere, but one can assume that, if the universe contains forms of life, then there is a possible chance of the existence of other forms of life in other places. We can also assume that life will exist and has existed, because time and space are relative. Now it depends...(guilty until proven inocent or inocent until proven guilty).
 
  • #16
Ophiolite
484
272
The central difficulty is that we do not yet know how life arose. mgb phys made the pertinent observation about life arising rapidly (in geological terms) after the formation, or rather the surface cooling, of the Earth. His conclusion is that this suggests life arises naturally and rapidly. There are two further possiblilities.
1. Life arrived from space.
2. This rapid abiogenesis was a unique, chance event.

The first of these alternatives increases the probability of life elsewhere. The second reduces it to zero. Until we have established how life arose, we have no way of reasonably selecting between these alternatives.
The question remains fascinating, worthy of study, but is currently unanswerable.
 
  • #17
WaveJumper
760
1
Life is comparable to a highly contageous planetary illness IMO. Whenever possible, it will colonise a host planet so i'd be truly surprised if it's not widespread in one form or another on most(if not ALL) relatively habitable planets.
 
  • #18
DaveC426913
Gold Member
21,363
4,823
Life is comparable to a highly contageous planetary illness IMO. Whenever possible, it will colonise a host planet so i'd be truly surprised if it's not widespread in one form or another on most(if not ALL) relatively habitable planets.
Well, a metaphor can only carry you so far. And that's all this is really, a metaphor. The mechanisms for infecting an organism and the mechanisms for colonizing a planet are unrelated (though again, you could find some nice metaphors).
 
  • #19
Ophiolite
484
272
Life is comparable to a highly contageous planetary illness IMO. .
In that case why have none of the other planets in the solar system caught a cold from the Earth? In the absence of evidence to support your hypothesis I would have to downgrade it to interesting speculation. (Or nice metaphor.)
 
  • #20
WaveJumper
760
1
In that case why have none of the other planets in the solar system caught a cold from the Earth? In the absence of evidence to support your hypothesis I would have to downgrade it to interesting speculation. (Or nice metaphor.)

Which part of my post didn't you get? The whole post said:

Whenever possible, it will colonise a host planet so i'd be truly surprised if it's not widespread in one form or another on most(if not ALL) relatively habitable planets.

May i suggest that you first familiarise yourself with the concept "Habitable Zone" before jumping to wrong conclusions:

http://en.wikipedia.org/wiki/Habitable_zone
 
  • #21
WaveJumper
760
1
DaveC426913 said:
Well, a metaphor can only carry you so far. And that's all this is really, a metaphor. The mechanisms for infecting an organism and the mechanisms for colonizing a planet are unrelated (though again, you could find some nice metaphors).

How do you know that? There is a chance that you may be right, but i want to see evidence that life was not brought here from space. Do you have a link to a website that claims abiogenesis is a fact?
 
  • #22
Coldcall
256
0
Anything that can happen once will most likely happen again given enough time. However modern science has encouraged us to believe that life is some sort of incredible fluke which somehow developed on an early Earth within 500million - 1 billion years of the planets formation. Arguably, that life took hold so fast here contradicts the "incredible fluke" of life.

My belief, and its only that, is that chaos theory (which is still very poorly understood) probably holds the answer to the development of life on a cosmic scale. Whatever laws of nature govern chaos theory could also be responsible for organising patterns which are conducive organising molecules into a form which is likely to evolve into lifeforms. The laws of physics might just be defaulted so that life is likely to self-organise given all the matter, energy and time available in this universe.

If this is the case then primitive life may not be as flukey as we once thought. However, it may take on average 4-5billion years of a sustainable habitat for intelligent and complex life to evolve from the simple single celled precursors.
 
  • #23
DaveC426913
Gold Member
21,363
4,823
However modern science has encouraged us to believe that life is some sort of incredible fluke
It has?? You're reading the wrong books.

Science is based upon observation. What do you observe about life in the Solar system, let alone the universe?
 
Last edited:
  • #24
DaveC426913
Gold Member
21,363
4,823
How do you know that? There is a chance that you may be right, but i want to see evidence that life was not brought here from space. Do you have a link to a website that claims abiogenesis is a fact?
Uh what? You think I'm making claims about abiogenesis?

All I'm saying is that your metaphor is just a metaphor. The thing about metaphors is that they can only be applied retrospectively. We see a difficult-to-understand phenomenon, and we notice a surface similarity to another, simpler phenomenon, so we compare them for the purposes of clarity.

A metaphor helps us understand what we already know. What it does not do is help us make predictions of things we do not know.

Seeing a draining sink as a metaphor for a hurricane (because they look similar) does not help us make scientific predictions about hurricanes. It might help students better understand a simplistic model of rotating systems, but they won't design any useful experiments to study hurricanes - to do that they'd have to study the actual phenomenon.

Your infection metaphor does not gain us any further knowledge in how the process of life works. In fact, it is likely to lead us astray because it is a surface-level comparison, not a deep fundamental comparison.


Note the distinction between a metaphor (a simplistic, surface comparison), and a model. There are definitely models of hurricanes (such as a tornado chamber, which mimics moisture and temperature diffs) that will help us understand them. but the key to a model is that it DOES mimic the important mechanisms in the real phenomenon; it mimics them at a deep, meaningful level, not a surface level.
 
  • #25
D H
Staff Emeritus
Science Advisor
Insights Author
15,450
688
i want to see evidence that life was not brought here from space. Do you have a link to a website that claims abiogenesis is a fact?
The latter sentence is disingenuous at best. The former sentence exemplifies how pseudoscience "works", but not how science works. Turning the table, do you have a credible source that shows that life was brought here from space and that abiogenesis cannot happen? That of course is an equally invalid argument. Those working on abiogenesis are looking at ways to bolster their own hypothesis with theory and evidence. They aren't there yet, but they have made incredible progress.
 
  • #26
baywax
Gold Member
2,157
1
Speaking of metaphors, the question "Does life here on Earth indicate life elsewhere?" is a perfect example of a person searching for a metaphor.

Does life on Earth serve as a metaphor for the rest of the universe? I don't think that's a good gauge to base a conclusion upon.

The best indication that life is elsewhere is when you find life elsewhere.
 
  • #27
WaveJumper
760
1
DaveC426913 said:
Uh what? You think I'm making claims about abiogenesis?

All I'm saying is that your metaphor is just a metaphor. The thing about metaphors is that they can only be applied retrospectively. We see a difficult-to-understand phenomenon, and we notice a surface similarity to another, simpler phenomenon, so we compare them for the purposes of clarity.

A metaphor helps us understand what we already know. What it does not do is help us make predictions of things we do not know.

Seeing a draining sink as a metaphor for a hurricane (because they look similar) does not help us make scientific predictions about hurricanes. It might help students better understand a simplistic model of rotating systems, but they won't design any useful experiments to study hurricanes - to do that they'd have to study the actual phenomenon.

Your infection metaphor does not gain us any further knowledge in how the process of life works. In fact, it is likely to lead us astray because it is a surface-level comparison, not a deep fundamental comparison.


Note the distinction between a metaphor (a simplistic, surface comparison), and a model. There are definitely models of hurricanes (such as a tornado chamber, which mimics moisture and temperature diffs) that will help us understand them. but the key to a model is that it DOES mimic the important mechanisms in the real phenomenon; it mimics them at a deep, meaningful level, not a surface level.


Life is comparable to an infection in as much as it's very resilient and hard to wipe out completely(and there is a good chance that it might have come from outer space). I don't think anything much weaker than the sun going out or Earth leaving its orbit can wipe out ALL life. That's why i used the metaphor and in that very sentence I said IMO. English is my second language, but I've come to understand that IMO stands for "In my opinion" which should give you a hint that i am not asserting life came from space. But just that in the lack of progress on abiogenesis, I'm inclined to think its origin might be alien. Here is the exact quote odf the statement i made:


Life is comparable to a highly contageous planetary illness IMO.


So generally speaking, my idea was that if life came from space, and it's as resilient as it is(and hard to wipe out completely), the closest comparision i could come up with was of a resilient, stubborn and hard to treat/wipe out mutating infection(mutating is an understatement). IMO, this a pretty good analogy.
 
Last edited:
  • #28
WaveJumper
760
1
D H said:
The latter sentence is disingenuous at best. The former sentence exemplifies how pseudoscience "works", but not how science works. Turning the table, do you have a credible source that shows that life was brought here from space and that abiogenesis cannot happen? That of course is an equally invalid argument. Those working on abiogenesis are looking at ways to bolster their own hypothesis with theory and evidence. They aren't there yet, but they have made incredible progress.

Are saying you know how science should work? Or how it works? Why do you insist that scientists should only examine the abiogenesis hypotesis? How would one individual's opinion matter to all scientists? I always thought that as far as the origin of life is concerned, all cards were on the table. What progress has been made on abiogenesis? Are talking about the Miller/Urey experiment? Or the jars recently found with the many amino acids inside? The purpose of abiogenesis is to find the origin of first RNA/DNA, not a chemical reaction that's necessary for life to exist. Since we know life exists, it's more or less obvious that amino acids are not hard to produce on Earth. I am not saying abiogenesis is impossible, i am merely not giving this idea more bias than the other theories.

Here you could read about the other possibilities considered by scientists from wikipedia's Origin of Life:

"Primitive" extraterrestrial life


An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially, either in space or on a nearby planet (Mars). (Note that exogenesis is related to, but not the same as, the notion of panspermia). A supporter of this theory was Francis Crick.

Organic compounds are relatively common in space, especially in the outer solar system where volatiles are not evaporated by solar heating. Comets are encrusted by outer layers of dark material, thought to be a tar-like substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation by ultraviolet light. It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth.

A recent experiment led by Jason Dworkin, subjected a frozen mixture of water, methanol, ammonia and carbon monoxide to UV radiation, mimicking conditions found in an extraterrestrial environment. This combination yielded large amounts of organic material that self-organised to form bubbles when immersed in water. Dworkin considered these bubbles to resemble cell membranes that enclose and concentrate the chemistry of life, separating their interior from the outside world.



Origin of life on wiki:

http://en.wikipedia.org/wiki/Origin_of_life
 
  • #29
Ophiolite
484
272
Which part of my post didn't you get?
I got all of it. I was simply emphasising the point made by DaveNumbers that you were offering nothing more than a colourful metaphor - that adds little to our understanding of what may have happened. Dave made the useful point that metaphors are useful in science once we understand what is happening. (Darwin's Origin was rich in metaphors as a way of clarifying the process he was explaining.)
May i suggest that you first familiarise yourself with the concept "Habitable Zone" before jumping to wrong conclusions:
Thank you for your advice. I am, however, deeply familiar with the concept of Goldilocks' zones. (You see, here a metaphor is valuable.) In this instance I'll use something closer to primary sources than wikipedia, if you don't mind.
The conditions on Mars at least are satisfactory for some forms of current Earth life. We don't seem to have detected any. (I am taking the consensus scientific position on this, within this thread. Personally, I think there is a very good chance that the Viking spacecraft did indeed detect life in the 1970s. Eventually, I hope, Gilbert Levin, the designer of the Labelled Release experiment, which returned the most convincing data, will be proven justified in his belief it detected life.)
No reason why it shouldn't be present on, or rather in Europa. There are perfectly suitable environments in each. I would accept the argument, if you wish to use it, that we simply have not tried hard enough yet to detect life.
... but i want to see evidence that life was not brought here from space. Do you have a link to a website that claims abiogenesis is a fact?
The conventional view, the default position, is abiogenesis on the Earth. Any textbook, mainstream paper, or quality 'popularising' site dealing with the origin of life will take this position. The alternative is abiogenesis somewhere else, with transport to the Earth. Either way in a Universe that has not existed eternally there has to be abiogenesis somewhere at some time, and nuclear synthesis of the elements has a lot to say about the time aspect. (Which I find quite ironic, since one of the main proponents of panspermia was Fred Hoyle, who helped give it a bad name,because his calculations of probability for protein synthesis were badly flawed, yet he was the very man who provided the insight into how most elements are formed.)
I would also second DH's comments on your request for evidence life was not brought from space. That's bass ackwards.

the closest comparision i could come up with was of a resilient, stubborn and hard to treat/wipe out mutating infection(mutating is an understatement). IMO, this a pretty good analogy.
Analogy, metaphor, simile, Pulitzer prize winning poetry, it still isn't science.
How did life reach the Earth? What form was it in? Where did it originate? How long was it in transit? What was the mortality rate during transit? etc, etc. Until some of these questions can be addressed with plausible numbers, panspermia is no better an option than in situ abiogenesis.

What progress has been made on abiogenesis? Are talking about the Miller/Urey experiment?
Just a side note. In my view the only reason the Miller/Urey experiment remains important is that it was the first serious attempt to investigate prebiotic chemistry. It's results are irrelevant, since the researchers did not appreciate the probable composition of the ancient atmosphere.
We do know, and you cite a good example, that complex organic chemicals can be produced quite easily by a variety of actions. uv light, impact, electric discharge, all work. And yes, those can work in space just as well as on a planet.
 
  • #30
baywax
Gold Member
2,157
1
Just a side note. In my view the only reason the Miller/Urey experiment remains important is that it was the first serious attempt to investigate prebiotic chemistry. It's results are irrelevant, since the researchers did not appreciate the probable composition of the ancient atmosphere.

There's nothing saying the Miller experiment doesn't describe the abiogenesis of life on another planet, then having it populate this one. Some forms of life are said to have the ability to got dormant in space then flourish upon coming into contact with a habitable planet... primitive or not.

Tardigrades (the water bear) can also survive exposure to extreme temperature (from –200 degrees C up to 151 degrees C). A recent experiment taking tardigrades into space, showed that they can withstand the cosmic radiation and vacuum of space travel. Although many did suffer UV radiation.

http://sciencephoto.blogspot.com/ [Broken]

(Good publication to subscribe to)
 
Last edited by a moderator:
  • #31
WaveJumper
760
1
Ophiolite said:
How did life reach the Earth? What form was it in? Where did it originate? How long was it in transit? What was the mortality rate during transit? etc, etc. Until some of these questions can be addressed with plausible numbers, panspermia is no better an option than in situ abiogenesis.


http://videos.howstuffworks.com/tlc/28848-it-came-from-outer-space-bacteria-in-space-video.htm


I am not saying abiogenesis is impossible, i am saying that IMO the blueprint of life(the encoded information in the mutating RNA/DNA that makes life possible) is of alien origin. Our planet Earth is very young - less than 5 billion years old, so if abiogenesis were possible, life elsewhere in the universe would be at least a couple of billion years older than the early Earth. That's assuming there is some form of life elsewhere in the universe. As Baywax said, some forms of life have the ability to live dormant for millions of years in the Arctic ice and become active when brought to warmer temperatures. See the above video link.
 
Last edited:
  • #32
Ophiolite
484
272
There's nothing saying the Miller experiment doesn't describe the abiogenesis of life on another planet, then having it populate this one.
Nothing, except for the inconvenient fact that the Miller/Urey experiment said nothing relevant about abiogenesis. All it produced was a few organic molecules, including some amino acids. There is a richer range of these already available in interstellar space.
Some forms of life are said to have the ability to got dormant in space then flourish upon coming into contact with a habitable planet... primitive or not.
Which is the second half of the reason I lean to panspermia to account for life on Earth.
Our planet Earth is very young - less than 5 billion years old, so if abiogenesis were possible, life elsewhere in the universe would be at least a couple of billion years older than the early Earth.
Not necessarily. Population II stars lacked the metallicity to produce terrestrial planets. It required multiple phases of stellar processing to put the required material into the interstellar medium. We may just be the first. Someone has to be.
 
  • #33
Bob_X
5
0
Maybe ...
If time goes to infinite, the probability =1. since life is just a form of some material things.
 
  • #34
DaveC426913
Gold Member
21,363
4,823
Maybe ...
If time goes to infinite, the probability =1. since life is just a form of some material things.
Unless you account for the heat death / big freeze, in which case, probability does not reach 1.
 
  • #35
Bob_X
5
0
Unless you account for the heat death / big freeze, in which case, probability does not reach 1.

Now the question goes to "what is time?".

Can the big freeze happens while time is going on?

Maybe heat death means the universe collapes to nothing and time fades away.
 

Suggested for: Does life here on Earth indicate life elsewhere?

Replies
11
Views
2K
Replies
11
Views
457
Replies
5
Views
210
  • Poll
  • Last Post
2
Replies
40
Views
4K
Replies
20
Views
3K
  • Last Post
Replies
1
Views
528
Replies
23
Views
1K
  • Last Post
Replies
6
Views
500
Top