Did life have its origin in outer space? Or did it originate separately on earth?
If life had its origin in outer space, is DNA ubiquitous throughout the universe or are there other types of replicating systems???
Is it possible to save endangered species without preserving adequate habitats for them?
Aren’t all these attempts to breed animals and take care of them in zoos and in the wild simply going to result in
domesticated versions of the animal over a period of time?
Aren’t most of these attempts futile?
The question on preserving species was meant to be a new thread. Please switch it over, Thanks
If you’re suggesting that the Earth went from molten lava to cooling and then an asteroid full of space faring single celled organisms crashed on Earth and became what would later be known as the current lifeforms of this planet, it’s very possible. Certainly just as probable as random protein strands turning into life on their own terrestially. Not much of debate one way or the other. Either it came from space or it didn’t, but neither gives more or less credence to the possibility of other life on other planets.
Also, mods can delete posts if you ask them (and they’re feeling kind), but they can’t move a post in one thread to another.
berdollos wrote:
I’ve heard there are bacteria – here on Earth – that have no DNA at all. They store all of their genetic information in RNA. (Anybody know what these RNA-only bacteria are called? I can’t find them with a google search.)
Terrestial life originating in space and arriving on Earth is one of my all time favorite crackpot theories. For one thing, it greatly expands the required time frame for such an amazingly complex thing such as DNA to “happen”. It has my bet.
Cool side point: if DNA life is ubiquitous in the Universe, there is a good chance that when we encounter life on other worlds, they will be edible! Assuming they dont have psuedopod and orifice disease.
Of course, the obverse is true.
“To Serve Man”
I’m not even going to weigh in with an answer, other than to say that no one has ever found DNA of extraterrestrial origin. If life was common in space, you’d think it’d be well-known in the mainstream by now. . . not just the pet project of Hoyle’s disciple, Wickramsinghe.
http://www.panspermia.org is just as wacko as it sounds, but there’s a soft spot in my heart for Fred Hoyle.
Also, there was a keen little item under “Astrochemestry” in this month’s Scientific American about some guys (who the SciAm editors choose to leave anonymous) who combined common compounds found in outer space, cooled them, and bombarded them with UV to create some organic goo. They submerssed that in water and got some cell-like spherules.
Though it is not available online, also in the April 2001 issue there’s an article called “Life’s Rocky Start” about biogenesis and minerals. I haven’t read it yet, though.
I’m pretty sure there are no bacteria with RNA instead of DNA; there are retroviruses, which are viruses which use RNA instead of DNA.
As for the OP: As Enderw24 said, in a way, it’s useless to speculate about this. Either it did or it didn’t. If we did find life on other planets using the same genetic code and so on, that would be convincing evidence of some sort of common origin. Otherwise, until we have some further facts, the simplest theory is that if there is life on Earth, it came from Earth.
Here’s a recent article with calculations on the interstellar dispersal of spores by meteors.
http://www.newscientist.com/dailynews/news.jsp?id=ns9999516
“Viruses”?
http://dorakmt.tripod.com/genetics/notes10.html
“bacteria only”–zip.
“RNA bacteria”–zip.
“RNA only bacteria”–ahh… 
You know how mitochondria were once independent purple bacteria that got “devoured whole” by early proto-eukaryotic cells, and became symbiotic with them?
Well … has anyone hypothesized that a similar thing might not have happened with self-replicating RNA in an “RNA World” scenario, and proteinoid microspheres?
Proteinoid microspheres have been observed to “eat” material from their their surroundings and “divide” when they get big enough. They’re pretty stupid in how they go about their “eating”, so they would tend to consume things that are “useless” to them in addition to the proteinoid “nutrients”. What if a proteinoid microsphere were to swallow a self-replicating RNA strand, and the two formed a symbiosis – the proteinoid microsphere protecting the RNA molecule, and the RNA molecule providing “information storage” services for the microsphere which would eventually enable it to direct the synthesis of advantageous proteins?
This hypothesis seems so obvious to me when I think about it that somebody else must have thought of it already…
Sorry to be nit-picky, but this is only a theory, and though probable, is not 100% confirmed truth.
I could be wrong, but I am pretty sure that there is no “self-replicating RNA.” RNA must be created from a DNA template through the process of RNA Transcription. I could be totally wrong here, but wouldn’t that make you’re hypothesis invalid?
This is the way it has been oberved in all Earthly organisms, but I don’t know if that precludes the idea of self replicating RNA. RNA and DNA are chemically very similar, the differences being that the “backbone” sugar of RNA is ribose, which has an extra oxygen atom over deoxyribose, and that uracil replaces thymine as a base. Uracil and thymine both pair only with adenine. If any biologists know why RNA can’t be the primary genetic carrier, I’d be interested to know.
How abiogenesis (start of life on Earth) happened is unknown. But it is possible that life started off-Earth. I think it will be an interesting area of research.
Even if our kind of life started in outer space, this would not mean that our kind of DNA is throughout the universe. Once our kind of DNA first came-to-be, there’s simply no way to transport it across the universe in less than the age of the universe. There would have to be some physical law that favors the formation of our specific type of DNA (and such a law is not known to exist).
I think it is very possible that other types of self-replicating molecules are feasible. Now we just need to figure out if they exist.
Now, the timescale for DNA diffusion throughout the Galaxy (on, say, comets, i.e. Oort Could bodies) might be a few billions of years.
Such a law is not known to exist, however, the fact that our DNA was formed like it was supports the theory that this formation is favorable. There has been life on earth for a long time, and in that time, the formation of DNA has probably evoloved along with the organisms that it is part of. After these last 6 billion years (or however long we want to say the world was around for) one might think that DNA has evolved for “optimal performance,” and that optimal performance would be the DNA that our cells contain. Therefore, if it involved in us, and worked, why would it evolve differently somwhere else?
And come to think of it, it really would make sense for there to be a general physical law that says something to this effect. For example, many of the same ideas or same types of products can be found in totally different cultures, before they had outside influence. This may be really pushing the boundries of analygies, but it makes sense to me…
Kaz wrote:
There are nucleic acids that can act as crude enzymes. It is theorized that it would be possible for an RNA strand with these “ribozymes” to be self-replicating – this is the basis of the RNA World hypothesis.
It seems to me that if the RNA World hypothesis is correct, and if proteinoid microspheres played a role in the development of the first cells, then the RNA might have “moved in” to the proteinoid microspheres the same way mitochondria are theorized to have “moved in” to proto-eukaryotic cells.
Is there any inherent advantage to having CAT (cytosine-adenine-thymine) equal histidine and TAC (thymine-adenine-cytosine) equal tyrosine, rather than the other way around? Perhaps, but it seems unlikely to me. (N.B.–IANABiochemist). It seems more likely that once the probably somewhat arbitrary “alphabet” of the genetic code was set, it would be very strongly conserved. The genetic code is about as fundamental as it gets, and I seem to dimly recall a principle or rule of thumb that more fundamental characteristics are more resistant to being changed and are more likely to be conserved. Even if we assume for the sake of argument that DNA is uniquely well-suited to being the information storage mechanism of life, and can be expected to be independently invented on many worlds, it seems to me that on some other planet, “TAC” might mean histidine and “CAT” might mean “tyrosine” (or “CAT” might mean “stop”, or “tryptophan”).
The bases of DNA and RNA (adenine, cytosine, guanine, and thymine/uracil) each have a specific, non-symmetrical molecular shape. A strand of DNA or RNA also has a direction, and is only “read” in this direction. When the cellular machinery is making a protein, each three letter sequence indicates either one amino acid or a “stop” signal, based on the shape of the sequence as a whole. Because the bases are not symmetrical, the sequence CAT is not simply the mirror image of TAC, and has a different shape. (Write the word CAT on a piece of paper and look at it in a mirror and you will see what I mean.) Therefore I think that if DNA and RNA are found on other worlds, then amino acids will be encoded in the same manner as they are here.
I’m not talking about whether or not CAT is a simple mirror image of TAC. I’m talking about whether there is something inherent in “cytosine-adenine-thymine” which equals “histidine”, as opposed to meaning “tryptophan” or some other amino acid. “CAT” is not a mirror image of “DOG”, but fundamentally there’s nothing inherent in the shapes C A T that means “cat” instead of “dog”. The shapes of the letters of our alphabet are pretty much arbitrary; the word for “cat” in Japanese or Arabic doesn’t look anything like the word for “cat” in English. (Even if you phonetically rendered the English sound for cat into katakana–no pun intended–it still wouldn’t look like “C A T”.)
So, is the genetic code arbitrary or not? I don’t really know. I suspect that it probably is, at least to a large extent. This Jehovah’s Witnesses page and this web page (which is actually about hemophilia but appears to have creationist sympathies) both quote a New Scientist article to assert that the existing genetic code “among the best of more than a billion billion possible codes”. On the other hand, this Duke University biology class notes page says that are “[n]o thermodynamic reasons to believe that the common genetic code is any better than a large number of other possible genetic codes”.
Any biochemists or evolutionary biologists care to weigh in on this?