Artificial Cells Developed: Communicate and Cooperate Like Biological Cells
The Daily Flash -Eco, Space, Tech (7/21)

Life in the Universe: "It May Not Even Have a Genetic Code"

Biocentric Why haven't we discovered signs of life beyond Earth? As Carl Sagan said, the absence of evidence is not evidence of absence. This thought is well known in other fields of research. Astrophysicists, for example, spent decades studying and searching for black holes before accumulating today’s compelling evidence that they exist. The same can be said for the search for room-temperature superconductors, proton decay, violations of special relativity, or for that matter the Higgs boson. Much of the most important and exciting research in astronomy and physics is concerned exactly with the study of objects or phenomena whose existence has not been demonstrated.

The search for life should not and cannot be limited to the search for Earth-like features. This cosmic view of the diverse nature of extraterrestrial life, is a revolutionary perspective which has the potential to make a great impact on our way of thinking as profound as the Copernican revolution.

We should be careful if we ever happen upon extraterrestrial life, Hawking warns. Alien life may not have DNA like ours: "Watch out if you would meet an alien. You could be infected with a disease with which you have no resistance."

Recently, scientists are content to define life using the "chemical Darwinian definition" that involves "self-sustaining chemical systems that undergo evolution at the molecular level." There are in fact a number of genetic-studies which purport to demonstrate that the common ancestors for Earthly life forms may have first began to form billions of year before the Earth was created. It has been speculated the first steps toward actual life may have begun with self-replicating riboorganisms whose descendants fell to Earth and other planets through mechanisms of panspermia, triggering the RNA world and then life as we know it. Life on some planets may be like life on Earth. Life on other worlds may have a completely different chemistry, and may not even possess a genetic code. 

Life that may have been originated elsewhere, even within our own solar system, could be unrecognizable compared with life here and thus could not be detectable by telescopes and spacecraft landers designed to detect terrestrial biomolecules or their products. Life might be based on molecular structures substantially different from those on Earth.

What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous, Hawking observed in his lecture, Life in the Universe. We can imagine  that one might have life with some other chemical basis, such as silicon, "but carbon seems the most favorable case, because it has the richest chemistry."

Organic molecules are now known to be common throughout the universe. Life, then, is assumed to be carbon-based.The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, Hawking observes, "some of these atoms came to be arranged in the form of molecules of DNA. One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated."

Other prominent scientists have warned that we humans may be blinded by our familiarity with carbon and Earth-like conditions. In other words, what we’re looking for may not even lie in our version of a “sweet spot”. Even here on Earth, one species “sweet spot” is another species worst nightmare. In any case, it is not beyond the realm of feasibility that our first encounter with extraterrestrial life will not be carbon-based.

As John Baross of the University of Washington has suggested, our present knowledge of physics and chemistry suggests that an organism could have an entire non-carbon-based metabolism such as silicon, which like carbon, can form four bonds. The greater reactivity of silicon compared with carbon may be an advantage in cold environments. Thus, its chemical and structural flexibility in non-aqueous environments can provide analogues to most of the functions of terrestrial biochemistry.

Silicon can form long chains as silanes, silicones, and silicates. Among them, silanes have been considered the most proper compounds to sustain life because they present the closest analog to hydrocarbons, which are so important to terrestrial life processes. However, such silicon-based life would have to be different from life as we know on Earth.

Alternative biochemists speculate that there are several atoms and solvents that could potentially spawn life. Because carbon has worked for the conditions on Earth, we speculate that the same must be true throughout the universe. In reality, there are many elements that could potentially do the trick. Even counter-intuitive elements such as arsenic may be capable of supporting life under the right conditions. Even on Earth some marine algae incorporate arsenic into complex organic molecules such as arsenosugars and arsenobetaines.

Several other small life forms use arsenic to generate energy and facilitate growth. Chlorine and sulfur are also possible elemental replacements for carbon. Sulfur is capably of forming long-chain molecules like carbon. Some terrestrial bacteria have already been discovered to survive on sulfur rather than oxygen, by reducing sulfur to hydrogen sulfide.

Nitrogen and phosphorus could also potentially form biochemical molecules. Phosphorus is similar to carbon in that it can form long chain molecules on its own, which would conceivably allow for formation of complex macromolecules. When combined with nitrogen, it can create quite a wide range of molecules, including rings.

So what about water? Isn’t at least water essential to life?

Not necessarily. Ammonia, for example, has many of the same properties as water. An ammonia or ammonia-water mixture stays liquid at much colder temperatures than plain water. Such biochemistries may exist outside the conventional water-based "habitability zone". One example of such a location would be right here in our own solar system on Saturn's largest moon Titan.

Hydrogen fluoride methanol, hydrogen sulfide, hydrogen chloride, and formamide have all been suggested as suitable solvents that could theoretically support alternative biochemistry. All of these “water replacements” have pros and cons when considered in our terrestrial environment. What needs to be considered is that with a radically different environment, comes radically different reactions. Water and carbon might be the very last things capable of supporting life in some extreme planetary conditions.

Casey Kazan 

Sources:

New Scientist

Alternative Biochemistry

Cosmology.com

Comments

So, according to the wise Carl Sagan, explorers in the middle ages would be correct in assuming just because they sailed thousands of miles without coming to the 'edge of a flat earth' that doesn't mean it isn't flat...

Such sophistry deserves sarcasm.

So, according to the wise Carl Sagan, explorers in the middle ages would be correct in assuming just because the sailed thousands of miles without coming to the 'edge of a flat earth' that doesn't mean it isn't flat...

Such sophistry deserves sarcasm.

Pga99, I'm going to guess that Sagan's comment relates to a lack of evidence that may one day be attainable through the use of SCIENCE, his comment is within a scientific context. I think it's silly for you to assume that his quote (a wise quote at that) pertains to ridiculous unscientific notions such as the earth being flat. The article even goes on to talk about a lack of evidence for black holes up until recent history and such. There is a lack of evidence for unicorns, do you really think Sagan would say that just because there is a lack of evidence for unicorns that doesn't mean they don't exist? Please use your brain next time you comment.

Riz,

I believe you need to heed your own advice...take a breath, remove your prejudices and re-read his post.
Sagan's intent and 99's response is simply this: Just because you cannot prove something exists, does not mean it does not exist. And vice versa...just because you cannot prove something doesn't exist, does not mean it exists.
I cannot prove there is a red Pontiac on I-94 this second. But there probably is, so my research as to why its there will continue...it's a safe bet.
This also applies to God, higher power, alien life, supernatural beings, etc.
For me to state that any of the above absolutely exist (including the Pontiac) would be absurd. I may believe they exist and will continue to search for proof but that it is where it ends.
Until now and the forseeable future, anyone who states they have proof of aliens, God, etc are either seeking attention or selling something.

You have provided a good list of element regimes that could form life:
1. Carbon
2. Silicon can form long chains as silanes, silicones, and silicates. Among them, silanes have been considered the most proper compounds to sustain life because they present the closest analog to hydrocarbons.
3. Arsenic may be capable of supporting life under the right conditions.
4. Chlorine,
5. Sulfur are also possible elemental replacements for carbon. Sulfur is capably of forming long-chain molecules like carbon.
6. Nitrogen and phosphorus could also potentially form biochemical molecules. Phosphorus is similar to carbon in that it can form long chain molecules on its own, which would conceivably allow for formation of complex macromolecules. When combined with nitrogen, it can create quite a wide range of molecules, including rings.

I would be like to know more about the potential of Chlorine, or is that an element that works as part of the Sulfur regime.

This is pure silliness, until you can provide evidence then your theory remains a theory and does not become fact. What basis do you use to even infer that life can possibly exist without DNA ? I don't have a problem with thinking out of the box but please do it within reason until you know otherwise.
The fact remains that on Earth life exists within a specific set of parameters, water being probably the most essential. Now if you assume that these parameters are not the only ones needed to create life and that it can literally spring up from host of other chemical interactions. Then why the hell don't we see loads of life all over the Solar System ? Assuming that life has multitudes of starting points means that it would have lots of chances to evolve into a more advanced specie. Why are we still searching for microbes and not skeletons ? You can only assume two things from this:

1) Life can exist in forms that we don't understand (which is what the article is saying). The odds of this border on the silly. What characteristics need to be shown by a cell/organism to prove that it "lives". It needs to respire (doesn't have to be oxygen) and reproduce (otherwise it goes extinct). Now why don't we see respiring and reproducing things all over the Solar System no matter how queer they look ?

2) You can assume that life isn't as commonplace and has a specific set of parameters, without these you get nothing ! This makes more sense to me given how hard it has been to discover alien life. However this does not mean that life is not commonplace. Given the size of the Universe the odds would make life commonplace even with obscure parameters for creation. The problem is human technology is too primitive to search for it.

You forgot robots. They're more likely to survive their carbon based masters in space.

Living cells as high as 41 km in earths stratosphere were detected by David Lloyd and Wainwright in 2004 using flourescent dye cyanine that only living cell membranes take up. Variation with height of cell distribution strongly indicates bacterial cell clumps are falling from outer space from 1/3 to 1 ton per day. Perhaps the planetary hosts like man are built from living precursors flourishing in outer space. Famous Hoyle showed evidence that nebula clouds contain amino acids like glycine, and sugars. Inside a thick huge dust cloud that doesn't condense into a star is plenty of heated water and many molecules. Hoyle believed that most nebulas contain a large percentage of dead remenants,some still living forms of bacteria, alage, microbes, etc. If this is the truth of panspermia that the scientific society wishes to dismiss, consider how the dinosaurs had their reign until the asteroids came.

You people really do have a limited oulook if you confine your thinking to purely biological forms of life!

Life could be so different than here on Terra we might not even recognise it!

One possibility ............ electrical!
Another............group conciousness!
Another................. some form of pure mental energy!

The possibilities are endless, but far be it for me to lecture all you smart people on how things work!

But just in case you're wondering..............!

You know my name, look up the number!

As silly as this may sound, I would rely on sound to find out life exists outside our realm. When I hear noises in a relative silence there is something living nearby, animal or higher intelligence. We are listening by way of radio telescopes to find the earmarks of intelligent life. On the other side our civilization has made electronic and light noise to be recognized, but with a limit of the bubble of our own making. Has anyone listened to us yet?

I think the problem is, "what is life" ? A robot isn't alive it doesn't die it can always be repaired or upgraded and we know exactly why it works. Why when a human dies we can't put in another "life force" and make it work again ? Can this "life force" exist in a non-organic vessel ? The answer seems to be "no" unless they can prove this http://www.dailygalaxy.com/my_weblog/2007/08/lifelike-dust-d.html which would broaden the horizons. For the time being the parameters for life are very much fixed. So even though an entity of "pure mental energy" sounds fascinating, I would have a hard time picturing one without a brain.

i think what is "silly" is the people who venture onto these pages and then talk as if he or she knos alll there is to kno in the universe and that in this kase life is only possible with karbon and water

the parameters that we kame into being with are what we kame into being from and just bekause it was our parameters doesnt mean that it would be the same for other environments

please dont be so narrow minded and assume that you understand the komplexity of the origins of life and what kan kreate it

any person on this earth that thinks we are the only life form in the universe, is a complete idiot. on a mathematical scale, our universe is so large and diverse, that its pretty much 100% guaranteed there is life. Thinking otherwise is ignorant and pathetic. as special as us humans like to think we are, i can guarantee there are much more beautiful things out there that would make us look so so very petty. Don't try the universe, it will win.

water is life in context, chemically in this universe

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