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Extraterrestrial Life --"Alternative Biochemistries" (Weekend Feature)




In his famous lecture, "Life in the Universe," Stephen Hawking observed that what we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous. 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."

Several eminent scientists think otherwise, that life in the universe could have a myriad of possible biochemical foundations ranging from life in ammonia to life in hydrocarbons and silicon. Silicates have a rich chemistry with a propensity for forming chains, rings, and sheets.

One of the founders on modern genetics, Cairs-Smith, argued that layers of crystalline silicates functioned as a primitive form of life on early Earth, before they evolved into carbon-based life forms.

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”. After all, 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 a solely carbon-based fete.

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, as we mentioned above 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.

While some of these scenarios may seem the stuff of science fiction, it's important to keep in mind that the foundations of life on Earth, the association of a protein with a nucleic acid when view abstractly, does little to convey the endgame wonders such as blue whales and Mozart's operas.

A billion years from now our descendants may have discovered other systems of physical life such as plasma within stars which would be based on the reciprocal influence of patterns of magnetic force and the ordered motion of charged particles. In fact, such life may well exist within our Sun.

Another form would be based on radiation emitted by isolated atoms and molecules in a dense interstellar cloud similar to the one physicist Fred Hoyle described in his scifi thriller, The Black Cloud. Such clouds can have a long lifetime lasting millions of years before they collapse.

Our personal favorite at The Daily Galaxy is the possibility of life in Neutron stars which wouldfbe based on the properties of polymeric atoms which which could form chains that could store and transmit information in a way that bears an uncanny similarity to the functions of nucleic acids -the molecules that carry genetic information or form structures within cells.

The Daily Galaxy 

Image Credit: antwrp.gsfc.nasa.gov

Stephen Hawking: Why Isn't the Milky Way "Crawling With Self-Designing Mechanical or Biological Life?"



Amazingly interesting article, i have said before on this site that searching for life under the assumption that it must be something like us, or live on a planet like ours, is a very small minded approach. In a universe so vast, in which we have not even fully explored our own solar system, there must be forms of life out there we cannot even conceive of existing. I think the universe is so saturated with the environments and building blocks for life, finding something out there is inevitable. Whether it will be intelligent self aware life is another issue entirely.

No offense to these scientists but Im pretty sure any other forms of life will be carbon based. Im still getting my undergrad in chemsitty but from what Ive seen no other element behaves quite like carbon. Silicon tends to form strong stable bonds with oxygen while the ones formed with carbon or pretty reactive. Phosphorous tends to form more than 3 bonds, unlike nitrogen. More can be listed but the premise is the same, the first row of elements and the second are similar but dont react nearly the same way. Extream heat, cold, etc does change the way things react but i feel like it is too chaotic to form complex life. I dont think its small minded at all to assume other life will be like us, like physics, chemistry is universal as is the formation of stars and their planets and thats what were banking on, that things tend to repeat themselves.

Like Carl Sagan said, he agrees that life out there is very likely to thrive on solvents other than water (citing ammonia and methane (or other hydrocarbons) as the two most likely). But, he further said due to the grandeur of carbon, if life was found out there with other elemental bases (besides carbon), carbon would most likely take up the undisputed throne in being by far the most likely to encounter base in life (especially in more complex larger forms of life).

As for star and black cloud based... whew, now that's a whole different story. It baffles me to think of it. The Black Cloud, neutron star based life, and let's not forget the dark matter based (since theoretically dark matter rarely interacts with regular matter, we would have one hell of a time detecting any dark matter based life that would literally be living amongst us <--- finally giving ghosts or the spirits the tiniest bit of credibility in science)


Physicists are fond of quoting Gell-Mann's Totalitarian Principle: "Everything not forbidden is compulsory." While Murry Gell-Mann intended this to apply specifically to particle interactions, it's been broadened to mean that anything that can happen will happen, somewhere, some time.

Thus, while carbon/water-based life may be by far the most likely in any given instance, I have no doubt somewhere out there we'd be able to find many planets where life has developed using other chemistries. If we look hard enough and long enough we might even find sapient life like that.

well, there are those things seen by tens of thousnds of people, referred to as flying saucers. We have not the technology to manufacture saucer shaped objects that fly, nor the technoogy to attain the speed they routinely do.
Owing primarily to gravity, which sags not only our bodies but also our organs, limiting our life span to 70-80 years on average. But for our life span, we would be far mre in telligent than we are, posess a body of knowledge much greater than we do.

We look for life as "we know it", for in our minds we are the "crown of creation". Can life exist in the universe that is not carbon based? We don't know the extent of the possible bounty that life can exist in, if only we stop looking for our selves in the reflecting pool of the universe. We want to explore the universe, so we can validate our existence. Science is about keeping an open mind of the possibilties that exist, not approaching things with a closed and preconcieved notion of what we will find.

Life can only exist in carbon based molecules, and so all life in the universe is carbon based. We are carbon based, so life has to be just like us.

As we search the universe for microbial life, asking if the primodial lifeforms are are based on what element. We do have to ask ourselves what would higher lifeforms be based on, and will we one day say, "to be able to see the forest for the trees".

it is arrogance and ignorance and self-absorption that makes us think we are the pinnacle the universe’s long effort(s) to nurture life forms. I react to the ‘Goldilocks’ concept with a grimace because it carries a sense we will somehow meet life with 4 limbs like us and who cut their toe nails with something like our dime store cutters tho maybe with elaborately exotic designs on the haft. The real problem to me concerns not the ‘form’ of life we will meet but life’s various schemes to survive and evolve, i.e., how many ways can a life form extend itself? Our earth mode of reproduction, DNA replication, is one mode of correcting for chain degradation and extending earth life forms forward in time. But, are there other ways not involving DNA? The usefulness of DNA as far as we can tell is it can encode ‘a lot’ of information and alternate algorithms for survival of a species. Are their non-DNA based possibilities? Are their other DNA-like 3-D morphologies either carbon or non-carbon based? The answer to this must be, ‘Yes’. A word on Ammonia and Methane as solvents to support alternative life forms - these solvents not only support analogies to water-base hydrolysis, the basis of our biochemistry, but at their liquid temperatures, they provide additional, modes of charge transfer that are magnitudes longer-lived, and faster, than available in water chemistry. This might give a basis for quicker reflexes and thinking?

Another thought - which will no doubt have many challengers and even objectors: earth life forms (certainly complex forms such as us), appear to be very inefficient bio-machines. We are energy-wise inefficient
and in constant search for energy sources. We mobilize around constantly leaking waste products from our multitude of different pores and orifices. We are prone to breaking down and we are short-lived. We must constantly pay attention to not falling outside our temperature rating - neither overheating nor getting too cold; we must constantly hydrate to achieve the best functioning of our biochemistry and machine cooling scheme; we must have access to the gas, Oxygen, but not too much or too little. We have circulating in our veins and capillaries a fluid made up of a mixture of garbage, exo-organisms we have to tolerate because they have assumed symbiotic, important roles in maintaining their (our) internal environment, a precise ionic strength and ion chemistry, and we have a continually chinking away sanitation and waste filtering system which if it goes down will see us die in short time. There is much more to this stream but ..the point of all this ‘reductio-ad-?’…I Just am not willing to buy any argument that we, as spokes-forms for earth life, are the Universe’s masterpiece or sole creation.

I personally think carbon based life would be the majority for life, just as most stars are red dwarfs. But there are other stars and I am just as sure other life might be likely to be found as well.

When you look at the range of extremophiles that eat things like arsenic, iron and petroleum it seems that in planets with less available resources or very niche conditions, other life might be adapted.

Perhaps carbon based life is the starting ingredient needed to have the greatest chance of initiasl evolvement but in a universe full of stars, it seems that the outliers must exist somewhere out there -- hybrids at the least.

We certainly don't know as much now as we like to think we do about the entire universe.

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