Is there life in the universe, and if so has it visited Earth?

[Vectus]

As for my thoughts on the matter--

What we know and the limited evidence we have suggests heavily that the universe could be teeming with life at every possible location. As suggested in an article linked earlier by Ivan, there is even the possibility that life so alien as to be fundamentally based on a different structure than ours may exist in droves in intergalactic dust clouds!

Just as we look on our own planet, life gives testament to its resilience. Aside from the very fact that it is still here after nearly four billion years and persisted through 5 or 6 major mass-extinction events, it not only exists, but thrives in the harshest of environments. We even have life that can survive unaided in space!

Given that even a tiny fraction of life may develop civilizations, it is indeed a real wonder why we have not encountered said intelligent life, when the prospects are so high of it being out there. I find this tantalizing to say the very least.


I think the most compelling argument to solve this issue is that we have not been looking long enough or even in the right ways. That to me is the most likely.

 

[DaveC426913]

Just as we look on our own planet, life gives testament to its resilience. Aside from the very fact that it is still here after nearly four billion years and persisted through 5 or 6 major mass-extinction events, it not only exists, but thrives in the harshest of environments. We even have life that can survive unaided in space!

Yes, but the question of how existing life survives has nothing to do with how non-life becomes life in the first place.

I find the most compelling argument to solve this debacle ...

I do not zink zat word means what you zink it means...
-Inigo Montoyez

 

[Vectus]

Yes, but the question of how existing life survives has nothing to do with how non-life becomes life in the first place.

My point is this: once life takes a foothold, next to nothing can get rid of it short of the planet being nearly destroyed or it's star going supernova.

Given the timescales involved, and even if the chance for life to arise turns out to be minutely small, we would still expect to see that it has cropped up all over the place.

I do not zink zat word means what you zink it means...
-Inigo Montoyez

It was like 4 am when I typed that. I must have been thinking of another word, which escapes me now. >.>

 

[DaveC426913]

My point is this: once life takes a foothold, next to nothing can get rid of it short of the planet being nearly destroyed or it's star going supernova.

I'll grant this, but:

Given the timescales involved, and even if the chance for life to arise turns out to be minutely small, we would still expect to see that it has cropped up all over the place.

I see where you're going but there's a logical disconnect.

If the chances of life arising are 1 in 200 billion over 13 billion years, then chances are it will have cropped up only twice in our galaxy. I grant that it might last virtually forever, which means, no matter how long ago they cropped up, they're likely still around. But there's still only 2 of them.

The fact that life appears to be tenacious has absolutely no bearing on how often it has arisen.

 

[Vectus]

The fact that life appears to be tenacious has absolutely no bearing on how often it has arisen.

Given. But let us not assume that there is only one chance for a life-capable planet to actually give rise to life. Over time, conditions may become more favorable to abiogenesis, the planet may be seeded via panspermia, or life may arise by other mechanisms that we do not know of or fully understand at present (terraforming, perhaps?).

That is all I meant. I find it wildly unlikely that we're the only ones out here given the amount of time we're looking at and the fact that nothing suggests our little mote of dust is special in any way.

Saying we're alone because of the results of our past and current search for life can be reckoned to shining a flashlight into a dark room for a couple seconds and declaring it empty. And I think that's actually giving it several orders of magnitude too much credit.

 

[DaveC426913]

Saying we're alone because of the results of our past and current search for life can be reckoned to shining a flashlight into a dark room for a couple seconds and declaring it empty.

No, it's equivalent to saying "We don't know if there's a mosquito in it."

 

[Vectus]

No, it's equivalent to saying "We don't know if there's a mosquito in it."

Well of course. We don't know until we know, right? :D

I wasn't trying to make an analogy to the rational stance of agnosticism towards the matter, but to the irrational stance that because of our inability to find life that it must be rare, despite everything else pointing to the contrary.

 

[imiyakawa]

I know for a fact, because I've witnessed what could be called a "UFO" (wasn't very unidentified though).

 

[Ivan Seeking]

I know for a fact, because I've witnessed what could be called a "UFO" (wasn't very unidentified though).

Would you like to share your story?

 

[junglebeast]

I know for a fact, because I've witnessed what could be called a "UFO" (wasn't very unidentified though).

The only thing that can be called a UFO is an unidentified flying object.

 

[GeekGuru]

Seeing how large the universe is, it is highly possible that there is other life out there. However, I doubt that they would visit us before we visit them. ;)

 

[Ivan Seeking]

However, I doubt that they would visit us before we visit them. ;)

Why?

 

[DaveC426913]

I know for a fact, because I've witnessed what could be called a "UFO" (wasn't very unidentified though).

How do you get from "seeing an unidentified flying object" to "life elsewhere in the universe"?

You saw something you cannot explain. Why do you automatically assume it is a product of alien life? Did you see a lifeform that was incontrovertably alien?

Because if not, your "fact" is a hasty conclusion.

 

[razored]

How do you get from "seeing an unidentified flying object" to "life elsewhere in the universe"?

You saw something you cannot explain. Why do you automatically assume it is a product of alien life? Did you see a lifeform that was incontrovertably alien?

Because if not, your "fact" is a hasty conclusion.

Almost everyone I know has this tendency---sometimes myself. Maybe it is because people are used to believing and accepting supernatural claims? These gullible people.

More generally used in religion : "my grandma was on her death bed set to die in a week from cancer, but then was cured completely of her illness. This is proof of god."

This person underwent spontaneous regression of the illness as opposed to some divine intervention. What if she had died, is that proof that a god does not exist? These arguments are seen everywhere.Original topic :
A good question that has no answer, as of yet.

Even if life were to exist theoretically---via drake's equation---somewhere in the cosmos, I find it highly unlikely that they would be able to travel here. The speed of light is the fastest traveling speed, so it would make sense that probably no life outside ours has been here yet. Maybe it has, but how would we know?

 

[baywax]

If extraterrestrials do visit us here, don't accept any blankets from them. In fact, we're done anyway if they do. They'll be packin' viruses and bacteria we've never been exposed to before or built-up an immunity to... so watch what you wish for baba.

 

[CEL]

If extraterrestrials do visit us here, don't accept any blankets from them. In fact, we're done anyway if they do. They'll be packin' viruses and bacteria we've never been exposed to before or built-up an immunity to... so watch what you wish for baba.

It is very unlikely that an alien virus could affect us. Viruses are adapted to their hosts. For example, the virus Phytophthora ramorum has killed tens of thousands of oaks since 1990, but it has no effect on human beings.
In the other side, oaks are immune to the flu virus.

 

[baywax]

It is very unlikely that an alien virus could affect us. Viruses are adapted to their hosts. For example, the virus Phytophthora ramorum has killed tens of thousands of oaks since 1990, but it has no effect on human beings.
In the other side, oaks are immune to the flu virus.

Thanks CEL, I can breath easier now. So, when the population of the first nations of North America were severely diminished by the small pox virus, which they'd never encountered before the european invasion of NA, was this because the virus had already adapted to humans and so was able to recognize and establish these aboriginal people (also human) as hosts?

 

[Vectus]

So, when the population of the first nations of North America were severely diminished by the small pox virus, which they'd never encountered before the european invasion of NA, was this because the virus had already adapted to humans and so was able to recognize and establish these aboriginal people (also human) as hosts?

Yes, basically.

The bacteria could still be a problem though, if it was particularly virulent and could survive and thrive on earth...

We would have antibiotics to combat them, but there is the potential that it could ravage our ecosystem. That would be much harder to avoid than getting an infection.

 

[CEL]

Thanks CEL, I can breath easier now. So, when the population of the first nations of North America were severely diminished by the small pox virus, which they'd never encountered before the european invasion of NA, was this because the virus had already adapted to humans and so was able to recognize and establish these aboriginal people (also human) as hosts?

Well, Vectus has already answered your question. I suppose you already knew that and have post your warning about blankets as a joke, but some people could take it for real, so I decided to mention oaks and humans, who share a common ancestor, and are not vulnerable to the same diseases.
If there is life in other worlds, it is very unlikely that they will use the same proteins as us and still more unlikely that they use DNA-RNA coding. As viruses are only small pieces of RNA, they can only infect DNA-RNA based life.

 

[baywax]

If there is life in other worlds, it is very unlikely that they will use the same proteins as us and still more unlikely that they use DNA-RNA coding.

What brings you to this conclusion?

 

[CEL]

What brings you to this conclusion?

There are hundreds of amino acids, but terrestrial creatures use only twenty of them to build proteins. It is unlikely that exo-organisms will use the same twenty.
As for DNA-RNA, nobody knows why and when terrestrial organisms started using it for coding genetic information. Unless it is the only way to code information, why would life elsewhere use the same coding?
When I say unlikely, I don't say impossible, only that there is little probability that it is so, unless we accept the theory of panspermia. If life has only one origin and has spread through the Universe from them, then it would use the same building blocks everywhere.

 

[DaveC426913]

Do viruses have to interact with our DNA to be a nuisance? What about their mere presence as foreign invaders? No, I guess they're little threat unless they can reproduce enough to hyperstimulate our immune systems...

 

[Vectus]

When I say unlikely, I don't say impossible, only that there is little probability that it is so, unless we accept the theory of panspermia. If life has only one origin and has spread through the Universe from them, then it would use the same building blocks everywhere.

Just wanted to point out that panspermia/exogenesis does not require that life have a single origin, just proposes the idea that life can be 'seeded' on a planet capable of supporting life (or that it was seeded on earth) from another source, such as comets, or debris from a large object colliding with another planet that may have already supported life.

 

[Vectus]

Do viruses have to interact with our DNA to be a nuisance? What about their mere presence as foreign invaders? No, I guess they're little threat unless they can reproduce enough to hyperstimulate our immune systems...

To even 'recognize' a target cell as a potential host, the virus must have a protein shell that can interact with the proteins and receptors on a particular cell's surface. Even if extraterrestrial viruses somehow developed a mutation that allowed it to invade some cells on Earth (which couldn't happen, as there would be no mechanism for such mutations to be selected for because the viruses still couldn't replicate), as CEL mentioned above, it is unlikely that they could inject their genetic code into the host cells to make them create new viruses because it is fantastically unlikely they use the same protein coding as life on Earth does. It would be like trying to bake a cake with a recipe that uses the same words as English, but with entirely different meanings.

Even more unlikely is that they would be able to effectively inject their genetic structure into the host cell's at all due to it being adapted to infecting cells with an entirely different form of coding than that of which life on Earth uses.

 

[DaveC426913]

To even 'recognize' a target cell as a potential host, the virus must have a protein shell that can interact with the proteins and receptors on a particular cell's surface. Even if extraterrestrial viruses somehow developed a mutation that allowed it to invade some cells on Earth (which couldn't happen, as there would be no mechanism for such mutations to be selected for because the viruses still couldn't replicate), as CEL mentioned above, it is unlikely that they could inject their genetic code into the host cells to make them create new viruses because it is fantastically unlikely they use the same protein coding as life on Earth does. It would be like trying to bake a cake with a recipe that uses the same words as English, but with entirely different meanings.

Even more unlikely is that they would be able to effectively inject their genetic structure into the host cell's at all due to it being adapted to infecting cells with an entirely different form of coding than that of which life on Earth uses.

uh... yes...

...which is why I was asking if the virus can be a problem even without interacting genetically.


i.e. foreign bodies frreely floating around in the system. They would be seen as invaders. Also, while they may not penetrate cells (and thus will not multiply), they will still interact with simpler molecules, snappong up oxygen or other simple chemicals.

 

[Vectus]

uh... yes...

...which is why I was asking if the virus can be a problem even without interacting genetically.i.e. foreign bodies freely floating around in the system. They would be seen as invaders. Also, while they may not penetrate cells (and thus will not multiply), they will still interact with simpler molecules, snapping up oxygen or other simple chemicals.

My apologies, it seemed to me that you were overlooking the fact that they can't replicate without infecting the cells. But no, they'd pose no threat for that very reason. Additionally, one reason viruses aren't considered life is because they do not metabolize, and therefore do not require even simple molecules to sustain such a metabolism.

Our immune systems are very adept at eliminating such foreign invaders and any threat they could possibly pose would be swiftly nullified. And the chances of the protein shell even being able to interact with any molecule in your body is near zero. I don't think it would be any different than if a few Phytophthora ramorum made its way into your blood stream.

 

[DaveC426913]

Additionally, one reason viruses aren't considered life is because they do not metabolize, and therefore do not require even simple molecules to sustain such a metabolism.

I wasn't thinking of metabolizing, I was simply thinking they were chemically reactive. But, of course, they're not (since that would be metabolism).

Our immune systems are very adept at eliminating such foreign invaders and any threat they could possibly pose would be swiftly nullified. And the chances of the protein shell even being able to interact with any molecule in your body is near zero. I don't think it would be any different than if a few Phytophthora ramorum made its way into your blood stream.

Right, of course. Our immune systems only have a hard time if something is able to multiply faster than it can dispose of them. It it doesn't multiply at all then it's basically no more a threat than any other inert gunk in the bloodstream.

 

[baywax]

There are hundreds of amino acids, but terrestrial creatures use only twenty of them to build proteins. It is unlikely that exo-organisms will use the same twenty.
As for DNA-RNA, nobody knows why and when terrestrial organisms started using it for coding genetic information. Unless it is the only way to code information, why would life elsewhere use the same coding?
When I say unlikely, I don't say impossible, only that there is little probability that it is so, unless we accept the theory of panspermia. If life has only one origin and has spread through the Universe from them, then it would use the same building blocks everywhere.

Because there are "hundreds" of amino acids does not mean they will all work as support for the evolution of life.

In nature there are many more variations amino acids than the simple 20
found in humans. However, when analyzing the human genome sequence,
there is a code for all 64 permutations (4^3), only some of them share
amino acids. This is a safe-guard (read "selection") against mutations of one or two
nucleotides. For example, the amino acid Alanine is coded with four
different nucleotide sequences: GCA, GCC, GCG, GCU.

http://www.Newton.dep.anl.gov/askasci/mole00/mole00213.htm

So there are amino acids to avoid as well as to utilize in the development of an organism.

But it is interesting what you say and the "mutations" that arise from the selection of "different" amino acids may be mutations that lead to a greater survival rate for that form of life. Interesting concept.

 

[CEL]

Because there are "hundreds" of amino acids does not mean they will all work as support for the evolution of life.

Terrestrial life! Different amino acids can lead to the formation of proteins, only not actual terrestrial proteins.
The fact that modern organisms use only those 20 amino acids, only indicates that the proteins formed with them are more suited to the terrestrial environment.

 

[baywax]

Terrestrial life! Different amino acids can lead to the formation of proteins, only not actual terrestrial proteins.
The fact that modern organisms use only those 20 amino acids, only indicates that the proteins formed with them are more suited to the terrestrial environment.

Yes, I get you're point. And here we are searching "super Earth's" and "earth-like" planets for
signs of life when... who knows, there may be amino acids formed from methane that can build another type of organism.

BTW, here's an article from tonight about an essential amino acid for life (as we know it) being found in the centre of a comet.

By Steve Gorman


LOS ANGELES (Reuters) - The amino acid glycine, a fundamental building block of proteins, has been found in a comet for the first time, bolstering the theory that raw ingredients of life arrived on Earth from outer space, scientists said on Monday.

http://ca.news.yahoo.com/s/reuters/090818/science/science_us_space_comet_life

These guys are so abiogenisis/earth-centric they can't imagine life starting 4.5 billion years ago somewhere else and slowly spreading throughout the galaxies via panspermia.

 

[CEL]

Another important point. Amino acids come in two flavors: left and right handed.
All proteins on terrestrial organisms use left amino acids, but this seems to be random. An extraterrestrial bacterium based on right amino acids could not digest our proteins and would be inoffensive to us.

 

[Anticitizen]

Yes, I get you're point. And here we are searching "super Earth's" and "earth-like" planets for
signs of life when... who knows, there may be amino acids formed from methane that can build another type of organism.

BTW, here's an article from tonight about an essential amino acid for life (as we know it) being found in the centre of a comet.



http://ca.news.yahoo.com/s/reuters/090818/science/science_us_space_comet_life

These guys are so abiogenisis/earth-centric they can't imagine life starting 4.5 billion years ago somewhere else and slowly spreading throughout the galaxies via panspermia.

There's a big jump between the idea of comets seeding our planet with amino acids, etc and the idea of living organisms actually hitching a ride on a meteor from another world.

I personally just don't buy it. As far as I can discern, the probability of a living planet being impacted by an asteroid strike, sending off fragments into space that contain some sort of bacteria or archaea, which then travel billions or trillions of miles (and thousands/hundreds of thousands/millions of years) to just happen to tear through our atmosphere and collide - delivering their payload still alive and intact after all that time and 'wear and tear' from vacuum, radiation, lack of nutrients - to be far more unlikely than simple-by-comparison abiogenesis.

Even allowing for panspermia, the life would still have had to evolve somewhere, so I don't get why you'd paint panspermia and abiogenesis as 'opposing sides' of some sort.

 

[Count Iblis]

http://arxiv.org/abs/astro-ph/0403049

 

[baywax]

Another important point. Amino acids come in two flavors: left and right handed.
All proteins on terrestrial organisms use left amino acids, but this seems to be random. An extraterrestrial bacterium based on right amino acids could not digest our proteins and would be inoffensive to us.

Do you have a reference re: left/right handed amino acids?

 

[baywax]

Even allowing for panspermia, the life would still have had to evolve somewhere, so I don't get why you'd paint panspermia and abiogenesis as 'opposing sides' of some sort.

I don't see abiogenisis and panspermia as opposing conditions. They can no doubt take place side by side.

What I'm pointing out is that conditions supporting life may have developed early on in the evolution of the universe, 5 - 7 billion years ago. This gives "life" time to go through some of the disturbances you mention with the asteroid bombardments etc. These occurrences would then have time to spread "space resistant" bacteria etc... on the tide of the development of the rest of the universe... to host planets, which would only be "host planets" in the time it took for water to form and other conditions met.