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How come almost no designers or worldcreators thinks about where and what their beings are coming from? And how a different evolution on a very different planet would affect life. The only way mamals could be on top of things here on Earth is because the dinosaurs died out 65 mio years ago, and left the place to us! 
Apollo 11 was the spaceflight that landed the first humans on the Moon, Americans Neil Armstrong and Buzz Aldrin, on July 20, 1969, at 20:18 UTC. Armstrong became the first to step onto the lunar surface six hours later on July 21 at 02:56 UTC. Armstrong spent about two and a half hours outside the spacecraft, Aldrin slightly less, and together they collected 47.5 pounds (21.5 kg) of lunar material for return to Earth. A third member of the mission, Michael Collins, piloted thecommand spacecraft alone in lunar orbit until Armstrong and Aldrin returned to it just under a day later for the trip back to Earth.- From wikipedia
Using what we have learned from life on Earth, what can we say about alien life? While it would probably be vastly different from life on Earth, alien life would probably adhere to certain universal guidelines, as the widely varying life on Earth does. These guidelines or ground rules include the following:Alien life would be governed by laws of physics and chemistry.
Alien life would be based on some type of chemistry (eliminating the sci-fi concept of pure-energy beings).
- Solvent - On Earth, the solvent for all of our biochemicals is liquid water. Other chemicals could be solvents as well, such as ammonia, methane, hydrogen sulfide or hydrogen fluoride.
- Temperature - Alien life may require temperatures at which its solvent can remain liquid.
- Pressure - Alien life may require environmental pressures (and temperatures) that allow solvents to exist in three states of matter (solid, liquid, gas).
- Energy source - Living things require energy to remain organized. This energy may come from a star or from chemical or geothermal energy (as in hydrothermal vents and hot springs). On any alien world, there would have to be some source of energy to sustain life.
- Complex molecules - Living things on Earth are organized and made of complex, carbon-based molecules that carry out biochemical functions. Carbon is a versatile atom that can form bonds with up to four other atoms, in many shapes, to make molecules. Although not as versatile as carbon, silicon can also form up to four bonds with other atoms and has been proposed as a basis for molecules of alien life (silicon-carbon hybrid molecules have also been proposed). It is likely that alien life forms would have some type of complex molecule to carry out similar functions.
Alien beings that are larger than microbes would have some equivalent of cells. As an organism gets larger, its internal volume (cubic function) grows faster than its surface area (square function). This places a limit on the organism's size, because substances from the outside of the organism must pass into and throughout the organism by diffusion, which depends upon large surface areas, short distances and differences in concentrations. As an organism grows larger, the distance to its center increases and diffusion gets slower. To maintain workable diffusion distances, an organism must have many small cells instead of one large cell. So, an alien would be multi-celled if it is larger than a microbe.
- Informational molecule - In Earth organisms, deoxyribonucleid acid (DNA) is a complex molecule that carries genetic information and directs the formation of other molecules in order for life to reproduce and function. Because a characteristic of life is that it reproduces, it seems likely that alien life forms would also have some type of informational molecule.
Alien life would evolve and adapt to its surroundings by the theory of evolution as previously explained.
The physiological make-up of a multi-celled alien would be most suited to its environment. Organ systems would be adapted to environmental conditions such as temperature, moisture and gravity.
A very nice article with a very straight forward approach, focusing on the nature and evolution of an alien world and whatever life might be found there. Especially that life on that planet ought to fit into it's native ecosystems, even if it has removed itself from it's natural place in the food chain (E.g. via civilisation), it would still have kept the same traits, physically as well as psychologic.
- The alien would have some way of bringing solids, liquids and gases inside its body, distributing them to every cell and removing waste products (equivalents of heart, blood vessels and kidneys, for instance).
- The alien would be able to take in energy from its surroundings, extract the energy and eliminate wastes.
- The alien would have senses (such as sight, sound, touch) to obtain information from the environment and respond to stimuli (while we use vision as our primary sense, this may not be true of aliens). They would also have some type of brain or nervous system to process information.
Alien organisms would probably have similar ecological structures to life on Earth.
- The alien would have some means of reproduction, either sexual or asexual.
- Population sizes would be limited based on the predominance of food, predators, disease and other environmental factors.
- Alien life forms would exist in food chains and food webs in their native environment, like life on Earth. Producers will make food, consumers will eat producers and/or other consumers and decomposers will recycle atoms and molecules from dead organisms back into the environment.
As you can see, life of any kind is intimately tied to its environment, so the characteristics of the planet would be extremely important in determining the characteristics of the life form.
- Alien life forms will be integrated with their habitats and ecosystems, like life on Earth.
"From the standpoint of physics, there is one essential difference between living things and inanimate clumps of carbon atoms: The former tend to be much better at capturing energy from their environment and dissipating that energy as heat.
Jeremy England, a 31-year-old assistant professor at the Massachusetts Institute of Technology, has derived a mathematical formula that he believes explains this capacity. The formula, based on established physics, indicates that when a group of atoms is driven by an external source of energy (like the sun or chemical fuel) and surrounded by
a heat bath (like the ocean or atmosphere), it will often gradually restructure itself in order to dissipate increasingly more energy.
This could mean that under certain conditions, matter inexorably acquires the key physical attribute associated with life."
I suck at math. I suck so bad at it, I had to become an artist. Or a bum. I choose the first. That's how much I suck at math."The distance to the Gliese 581 system is what gets me excited: it’s 20 light years away. This planet is about 3 times the Earth’s mass, and it orbits its star in the right place. We don’t know what it’s made of, if it has an atmosphere, or really very much about it at all! But given its mass and temperature, it’s potentially habitable. Extrapolating from our one example, let’s say that habitable planets are roughly 20 light years apart in the galaxy (as we’ll see, that number can be a lot bigger or smaller, and the end result is still cool). That means there’s one star per cube 20 light years on a side:
In the drawing, each box is centered on a star, and the two stars are 20 light years apart. That means the cubes are 20 light years on a side, right? If we assume stars with livable planets are distributed throughout the galaxy like this, then there is one star per 20 x 20 x 20 = 8000 cubic light years. That’s the density of habitable planets in the galaxy.
So how many cubic light years are there in the galaxy?
A lot. Let’s say the Milky Way is a stubby cylinder 100,000 light years across, and 2500 light years thick. The equation of volume of a cylinder is
volume = π x radius of disk2 x height of disk
so
volume = π x 50,0002 x 2500 = 2 x 1013 cubic light years
Holy wow! That’s 20 trillion cubic light years!
Now we just divide the volume of the galaxy by the density of stars with planets to get
2 x 1013 / 8000 = 2,500,000,000 planets
Oh my. Yeah, let that sink in for a second. That’s 2.5 billion planets that are potentially habitable!
Even if my numbers are way off, there could be as few as hundreds of millions of planets, or as many as maybe hundreds of billions in our galaxy alone that we could live on!
Again, the point being that mathematically speaking, there may be a lot of habitable planets out there. And who knows; some may be marginally habitable and we can terraform them. And then there are moons of worlds, too… I don’t think I’m speaking too far out of school if I were to speculate that for every perfect Terra Nova out there, there might be three or four more planets we could live on with some work.
Of course, I’m ignoring how we’d get there! But that’s an engineering problem, and given enough time — oh, say, a century or two — I imagine we can overcome a lot of those issues."Then there's all the other details - as one reader intelligently replies:
Remember that the Earth itself was incapable of supporting modern humans until almost 500 million years ago — that is, for 8/9ths of its existence. The rest of the time there was no oxygen in the atmosphere, or not enough, or there was no ozone layer, or carbon dioxide levels were so high that humans would be unable to breath.
Then there is the problem of composition. A world where sulfur dioxide or hydrogen sulfide are part of the planet’s respiration system would kill terrestrial life off pretty quickly. The planet’s crust might have a lot of toxic compounds that, if they didn’t kill terrestrial plants, would kill animals who ate those plants. Where there is only a vanishingly small chance that an exo-world would harbor a toxic virus or other pathogen, there is a much higher likelihood that the planet would have annoying — even fatal — allergens. And how many soaps, solvents and preservatives have we invented that mimic estrogen and other hormones? It is unlikely that other worlds would have naturally occuring compounds that pose a similar risk to human health?
"If earth ceased rotating about its axis but continued revolving around the sun and its axis of rotation maintained the same inclination, the length of a year would remain the same, but a day would last as long as a year. In this fictitious scenario, the sequential disappearance of centrifugal force would cause a catastrophic change in climate and disastrous geologic adjustments (expressed as devastating earthquakes) to the transforming equipotential gravitational state.
The lack of the centrifugal effect would result in the gravity of the earth being the only significant force controlling the extent of the oceans. Prominent celestial bodies such as the moon and sun would also play a role, but because of their distance from the earth, their impact on the extent of global oceans would be negligible."
"If the earth's gravity alone was responsible for creating a new geography, the huge bulge of oceanic water—which is now about 8 km high at the equator—would migrate to where a stationary earth's gravity would be the strongest. This bulge is attributed to the centrifugal effect of earth's spinning with a linear speed of 1,667 km/hour at the equator. The existing equatorial water bulge also inflates the ellipsoidal shape of the globe itself."
"If the earth stood still, the oceans would gradually migrate toward the poles and cause land in the equatorial region to emerge. This would eventually result in a huge equatorial megacontinent and two large polar oceans. The line that delineates the areas that hydrologically contribute to one or the other ocean would follow the equator if the earth was a perfect ellipsoid. However, due to the significant relief of both the continents and the ocean floor, the hypothetical global divide between the areas that hydrologically contribute to one or another ocean deviates from the equator significantly. "
