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

[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.

 

[CEL]

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

Look at
http://chemistry.about.com/library/weekly/blaminochiral.htm
or google for chirality

 

[i.neu]

Perhaps there is, perhaps there isn't life "out there". astrobiology/exobiology is still very, very young...we can't formulate anything compelling about life in the universe, yet.As for the Drake equation, it's certainly a long shot... maybe the "Drake Guess" is a more appropriate term than the "Drake Equation".

That being said, I shall adopt the sceptic's position when it comes to extraterrestrials holidaying on Earth. :)

 

[ideasrule]

That being said, I shall adopt the sceptic's position when it comes to extraterrestrials holidaying on Earth. :)

Hush. I'm not "holidaying"; I'm doing scientific research. Don't you see the difference?

 

[baywax]

Look at
http://chemistry.about.com/library/weekly/blaminochiral.htm
or google for chirality

I still don't think there will be many life forms beyond the types and species we see on earth... and that is one very large number of variations on life.

Vertebrate Animals

Mammals 5,416
Birds 9,956
Reptiles 8,240
Amphibians 6,199
Total Vertebrates 59,811

Invertebrate Animals

Insects 950,000
Molluscs 81,000
Crustaceans 40,000
Corals 2,175
Others 130,200
Total Invertebrates 1,203,375

Plants

Flowering plants (angiosperms) 258,650
Conifers (gymnosperms) 980
Ferns and horsetails 13,025
Mosses 15,000
Red and green algae 9,671
Total Plants 297,326
Others
Lichens 10,000
Mushrooms 16,000
Brown algae 2,849
Total Others 28,849

TOTAL SPECIES 1,589,361

http://www.currentresults.com/Environment-Facts/Plants-Animals/number-species.php


And these are only the known species. At some point we may see a pile of methane that moves and eats and reproduces... but I really doubt it.

 

[DaveC426913]

Invertebrate Animals

Insects 950,000

And 350,000 of those are beetles.

"One thing we can be sure of about God: he had an inordinate fondness for beetles.”