Why do people always use Earth as a model for alien life?

Question

Somebody just asked if there is alien life. Invariably the answerer tries to estimate the number of planets like ours. Water, temperature, etc.

Why does alien life have to follow the earth model? Couldn't it be based on something other than Carbon, not need water, etc.,etc.,?

We are just a speck in the Universe and if somebody can fathom that I don't see why they can't take the next step and realize alien life may have evolved in ways far different from the Earth's model.

Answer 1

I understand exactly what you're saying. The problem is that carbon based life forms are the only kind we've ever known so we don't have the knowledge to understand any other kind of life. Who knows, we may have found life already and just didn't realize it because it was too different from anything we've experienced.  

Answer 2

http://en.wikipedia.org/wiki/Silicon-bas...

The most commonly proposed basis for an alternative biochemical system is the silicon atom, since silicon has many chemical properties similar to carbon and is in the same periodic table group, the carbon group.

But silicon has a number of handicaps as a carbon alternative. Because silicon atoms are much bigger, having a larger mass and atomic radius, they have difficulty forming double or triple covalent bonds, which are important for a biochemical system. Silanes, which are chemical compounds of hydrogen and silicon that are analogous to the alkane hydrocarbons, are highly reactive with water, and long-chain silanes spontaneously decompose. Molecules incorporating polymers of alternating silicon and oxygen atoms instead of direct bonds between silicon, known collectively as silicones, are much more stable. It has been suggested that silicone-based chemicals would be more stable than equivalent hydrocarbons in a sulfuric-acid-rich environment, as is found in some extraterrestrial locations. In general, however, complex long-chain silicone molecules are still more unstable than their carbon counterparts.

Another obstacle is that silicon dioxide (a common ingredient of many sands), the analog of carbon dioxide, is a non-soluble solid at the temperature range where water is liquid, making it difficult for silicon to be introduced into water-based biochemical systems even if the necessary range of biochemical molecules could be constructed out of it. The added problem with silicon dioxide is that it would be the product of aerobic respiration. If a silicon-based life form were to respire using oxygen, as life on Earth does, it would possibly produce silicon dioxide as a by product of this, assuming that the only difference between the two types of life is the presence of silicon in place of carbon.

Finally, of the varieties of molecules identified in the interstellar medium as of 1998, 84 are based on carbon and 8 are based on silicon. Moreover, of those 8 compounds, four also include carbon within them. The cosmic abundance of carbon to silicon is roughly 10 to 1. This may suggest a greater variety of complex carbon compounds throughout the cosmos, providing less of a foundation upon which to build silicon-based biologies, at least under the conditions prevalent on the surface of planets.

Answer 3

Of course, but we already know that carbon & water-based works.

We've only recently appreciated it works in hostile environments.

Answer 4

Only very few people like Late Carl Sagan has the mental ability to think extra tereestrial life forms.We only know the life forms we see on the earth.So natuaraly we compare it with what we has seen.

There are possibilities of millions of other forms tha live in different worlds.

Answer 5

Yes, scientists think about this a lot.  The thing is, there is no other element that is as versatile as carbon.  Unless the laws of atomic physics are different in other locations (which I guess they could be) then this will be true everywhere.  Silicon can have similar reactions, but they don't take place nearly as quickly.

That doesn't mean that we need to look for water and temperatures comfy for us, though.  For example, some speculate the Saturn's frozen moon Titan could have life that is based on liquid methane.  (Methane is part of natural gas, which many people use as a fuel to heat their homes.)  It's so cold there that what we call natural gas is a liquid there. They have already taken pictures of liquid methane lakes on its surface. No creatures that live there could possibly live here, and vice versa.  

Answer 6

I completely agree with you.  Most people have their head so far up their butts that they can't think out side of the box.  For all we know there could be a planet entirely comprised of a liquid substance that the planets inhabitants use for breathing. they could swim in air and breath water. ya know?  the possibilities are endless.  I think that somewhere in the universe there is a species that looks like card board boxes and eats solidified hydrogen bars for sustenance.  Your right do space creatures have eyes, or ears or mouths or arms or legs?  It's to soon to tell but its fun to just come up with the craziest of ideas.  

Answer 7

It doesn't have to follow our model. A part of my mind has always thought like that. Actually, who says that we're the only type of beings? No one knows. We know a lot through the discoveries that we have made, but there's so much that we don't know that we can't even fathom that we don't know it. See, I wish that we stop treating each other like shitt. And realize that we're all human. I would be so much more concerned if aliens came to explore who we were. I wish sci-fi movies really touched on how humans and aliens would react. Alright, gotta bounce. 1

Answer 8

We use Earth as a model because as far as we know, it is the only planet with the right conditions for life. This way, astrobiologists have an idea of what life can be like.

Answer 9

Anything and everything we call life depends on water.  It's polarised molecules act as a form of infrastructure inside cells without which, none of the chemistry we call life would take place.

Even viruses that in themselves do not contain water must live in a water-bearing enviroment for them to do what they do.

If by 'life' you mean some entity that can reproduce itself if it is in a suitable environment, then indeed, no one can say for certain there are no other possible self-reproducing structures but anything that exists at the temperatures we do would obey the same rules as we do.  Could something strange live in the outer layers of the sun, but when it gets ejected towards Earth it cools too much and essentially freezes to become something unrecognisable from what it was?

No-one can say no!  

Answer 10

Understandable  challenge.

Well, I'm sure it's just because we are the only place that we know of that can sustain life.

And most like to rely on hard scientific evidence, not just 'what ifs.'