Possible Alien Life

[CraigD]

I’m strongly skeptical that any of our more definite speculations about alien life, interesting, thoughtful and informed thought they may be, are likely to be correct.

In contrast to Physics, most of what we know to be true of terrestrial biochemistry is due to empirical discovery, not theoretical prediction, explanation rather than hypothesis. The common statement belief that “Extraterrestrial life will likely have DNA, because we are unable to propose an alternate biochemistry as effective as it” implies that we deduced the existence and structure of DNA from first principles, and failure to deduce an attractive alternate model is informative.

The only speculation I feel confident making is very general: Extraterrestrial life will be surprising.

On a gross anatomical level, I think Arthur Clarke’s recent speculation about ET Life is interesting. This idea suggest that life may be very common, existing on nearly any planet even remotely able to sustain it, but may be predominantly terribly boring, conmsisting of very simple organisms competing on the basis of metabolic efficiency and little else, such as worlds dominated by photophilic ozzes and slimes. The evolution of complex life may be very unusual.

[lindagarrette]

Did anyone see "Alien Planet?" I just turned in the DVD and don't recall the source but I thought it was imaginative and worth an hour or so of entertainment. Fortunately it assumed the laws of physics apply universally and there were a lot of other assumptions, such as that life evolves, and that it requires a stable environment like the earth.

I suppose its possible that another form of DNA could lead to completely different life forms assuming evolution is part of the definition of life. ;There could even be one life form on a planet, an individual, living alone without growing or replicating, but then how could it survive? I think if we find anyone out there or if it finds us, it will have a face.

[HydrogenBond]

The laws of physics are assumed to be the same throughout the universe. With the longest life subparticle composites of the universe everywhere in the universe, i.e., electrons, protons and neutrons, it follows that chemistry is also universal. The environment will determine which equilbrium chemistry is available. An acid planet will be different than a basic planet but both will follow the laws of chemistry. The heavy planet may cause crystals to form differently than on a light planet but the same laws of chemistry should apply.

The carbon atom and DNA, RNA which is the basis of life on earth is probably the only chemistry that can support rapidly evolving life. The only other atom core that may have a shot is Si. It is below C on the periodic table and does a lot of what carbon does. The problem with silcone based life is that silcone macromolecules are very stable and not easily broken down. That is why they are used for breast implants, low temperature break fliud, superballs, carwax, etc.. The molecules of life need to be able to change more easily so that evolution can pertubate to the future.

DNA, RNA on earth provides for amazing diversity, where various critters are uniquely suited to that environment. Alien life could also be a odd diversity based on their environment to which they have become suited. Superfiscial diversity is what we see, but underneith the skin we are very anatomically uniform. All aminals have a heart and brain even though one crawls and the other flies.

[HydrogenBond]

Here is an interesting angle on aliens. Let us reverse engineer our image of aliens and deduce its home environment. The aliens of sci fi, tabloids, and witness account have big eyes, big heads and frails bodies. The big eyes migth tell us that there is low light level on their planet. Evolution would create bigger visual sensory systems to pull in the lower light level or light at higher wavelength such as IR. This would explain sitings being more common at night and why they hide during the day. Thier frail bodies might mean low gravity on their planet causing their muscle mass not to develop. Or could be an artifact of long space travel. This would be a reason to stay inside their space craft. Their puny bodies might imply small lungs suggesting their planet or space craft having a higher concentration of oxygen in its atmosphere. Their big head implies bigger brains or thicker skulls. The bigger brains could mean higher intelligence while their thicker skulls might be need to protect a more frail brain configuration. Maybe less gray matter and more white matter. This would make them good con artist and less law abiding (another forum). Maybe they are not explorers but escaped criminals or maybe visionaries. The criminal visionary angle is more conisitent with their shy and cautious behavior

[BlameTheEx]

Before assuming that alien life will be much like earth life it is a good idea to consider earth life. All of it, including prehistoric.

2 eyes are not inevitable. Look at the spider. My guess is that out in the universe forward facing vision is an oddity. An animal with all round vision has the advantage.

Bilateral symmetry is probably popular but not inevitable. We have had a fair number of 5 sided species like the starfish. Think of an alien with say, 3 eyes, legs, and arms. No reason that it have total symmetry any more than we have out hearts in the centre. The mouth might have migrated to one side and the internal organs to wherever is practical. A modified 3 way symmetry.

Most evolution has occurred underwater on earth. The starting point would probably be the same as on earth - the development of weapons. Flint can just as easily be shaped under water. Farming and group hunting would develop just as easily along with the domestication of animals. I question the idea that fire is necessary to develop intelligence. Assuming volcanic activity (Probably necessary for a viable planet) there should be plenty of heat to power an industrial revolution. Research powered by volcanic vents! All told air breathing intelligence is probably the exception rather than the rule. Think intelligent octopi.

Finally we could consider a creature, or plant, with intelligent control of its body. Organs grown at will. Biological rather than flint weapons starting the push to intelligence. A civilisation based on regulating, developing and trading genes. How is that for intelligently adapting to a changing environment? Of course such a creature probably wouldn't define us as intelligent!

[HydrogenBond]

If humans evolved from apes we were vegatarians at one time. Fire helped the early humanoid veg gatherers become carnivores. Fire changes the texture of animal flesh making it easier to digest. Becoming omnivoros allowed human to survive the ice, because the sparse twigs and berrys were eatened by the herding animals. The fire also kept them warm. Maybe one of the cavemen looking to keep their fire going decided to threw in a dead refridgerated animal into the fire, figuring it would burn like wood. When it began to smell good enough to eat; the rest is barbeque.

As far as aliens anything is possible considering the variety here on earth. Evolving from water is makes sense but higher evolution would face certain problems. The first being dissolved oxygen for brain development. Whales have large brains but require a lot of bulk. Space travel would be difficult to develop because the having to carry around all that water weight.

[CraigD]

Originally Posted by HydrogenBond

If humans evolved from apes we were vegatarians at one time.

Modern apes aren't vegitarians. It's unlikely ancient ones were much different.

Virtualy all primates suppliment a primarily fruit and leaf diet with insects and other small animals. Chimps hunt and eat animals only a few times smaller than themselves (eg: monkeys). Depending on their habitat, baboons may get more of their calories from meat than the average human, and have been known to prey on animals as large as domestic sheep and goats.

Although humans digestive systems are significantly different than other living primates, the difference is not so great as was once thought. For instance, when I last attended a biology class that covered the subject, I was taught that humans are digestively incapable of subsisting on a chimp-like diet where leaves are a staple. In the 1980s, however, this assumption was tested by the simple expedient of having a bunch of grad students eat leaves for a couple of weeks, revealing that, while less optimally than chimps and gorillas, humans can in fact obtain adequate calories from leaves, via the same mechanism as these other primates (fermentation-like activity in the large intestine).

Grad students are great. Privileged are those who have them.

[HydrogenBond]

Here is an interesting angle. If a species of giant aliens appeared which were omnivors, to take over the earth , America might be spared. We are overweight as a culture and might be considered too high in chloresterol.

[Boerseun]

All very good points.

However, continuing along UncleAl's reasoning a few posts ago, I'm sure that for similar planets, roughly similar solutions should develop.

Consider:

Oxygen in our atmosphere is plant waste. Animals thrive on it, and is dependent on enough plants being around so that they'd have a breathable atmosphere. CO2 in our atmosphere is animal waste, and conversely, plants thrive on it. They, too, are dependent on animals being around to continuously inject CO2 into the atmosphere. Sure, every now and then a volcano spews forth CO2, but plant life can't be successful based on unreliable volcanos. So, they are dependent on animals.

With this, we have achieved a dynamic system where resources like oxygen and carbon is continuously circulated throughout the biosphere. If this wasn't the case, then Life would have thrived, reliant on one specific element until it's used up. It's not being dynamically injected into the system, and the whole system would collapse.

So, making an observation of Earthlife, I suppose we could say that a biosphere of two vastly different life-forms (plant-life and animal-life) might also be essential. I suppose if the popular notion of Hollywood-biped large-eyed huge-brained aliens holds any truth, we can probably safely assume that their home planet should also harbour something similar to plant-life on Earth. Not?

[HydrogenBond]

Molecular oxygen or O2 is a plant bi-product, but only during the day when there is light for photosynthesis. Without light they use O2. The nitrogen or N2 within the atmosphere may have formed from bacteria, since bacteria exist that can convert nitrate into nitrogen gas. This shows that life can obtain oxygen from nitrates and sulphates to name a few without an oxygen atmosphere.

The CO2 as being an animal waste product is true, whoever the amount of CO2 within limestone deposits is too concentrated and localized to be explained it by coming from animals alone. Volcanoes show that CO2 is a natural product of the earth, stemming from conditions where life cannot exist. The existance of sulfides or hydrogen sulfide vents also shows reduction potential still existing within the earth even without the sun. This allows life to evolve even without photosynthesis.

Here is speculation for the natural formation of O2 by the earth itself. To form O2 from O (oxide) would require oxidizing oxygen. Since chlorine is more electronegative than oxygen, if both came from a mantle plasma where all the outer electrons are ionized, slow cooling might shift the lion's share of electrons to Chlorine to form Cl-. The oxygen's deficit of electrons might form O2 for stability. If hydrogen was in the plama mix hydrogen peroxide and Cl- might formed. Additional H as HCL would kick off the oxygen gas to make water.