A biology question

[Shirastro]

As an astronomy enthusiast (with very little actual scientific knowledge) and a complete lack of knowledge of biology there is one thing that always puzzled me whenever i would watch one of those shows about space, and more specifically about searching for extra-terrestrial life.

Why do we always assume that for the life to exist, the conditions on the planet have to be at least somewhat similar to those of earth?
More specifically the presence of liquid water.

Now i can understand why it's safe to assume that there is no life on super cold or super hot planets, due to the fragility of the organic matter, but why is H2O considered a magical ingredient for life.

Couldn't life come to existence and evolve in, let's say, a lake of sulfured acid....or even better a lake made out of some other element that we haven't discovered yet?

Also couldn't some life forms evolve in such a way that they breathe nitrogen or CO2 instead of oxygen?
Can life come to existence in a completely different environment?


I remind you that my knowledge of biology is very very limited, so i would like someone with a bit more insight to explain those things to me

 

[Nuuu]

Knowing probably as little Biology as you, i would say that they probably could, we just don't know yet because all life we know thrives on Oxygen and Water.

 

[WaReloaded]

I was going to give an explanation (I don't have a completed Bachelor of Science degree...yet) but this explains it better than I ever could.

http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Silicon_biochemistry

 

[Aidinthel]

It's much simpler to look for conditions that we already know can support life rather than guessing randomly.

 

[Wheeleybird]

I thought it was because of the higher electronegativity of the oxygen in the water making it such an extraordinarily great solvent compared to other H2X groups? Then some mumbo jumbo about needing an aqueous environment for efficient means of transport (it's been a while since I did this) required in living organisms...

This could be completely wrong, I didn't do too well in that semester but that's my say.

 

[Phlakes]

Well, just like people usually imagine other people as members of their culture, we naturally think other life would be similar to us.

 

[Dags90]

Couldn't life come to existence and evolve in, let's say, a lake of sulfured acid....or even better a lake made out of some other element that we haven't discovered yet?

Also couldn't some life forms evolve in such a way that they breathe nitrogen or CO2 instead of oxygen?
Can life come to existence in a completely different environment?

A note, acids aren't acids without water. Acid actually refers to altered water molecules (hydronium ions), and the property of certain chemicals to create these species.

There are organisms which use things other than oxygen as a final electron acceptor (the role of oxygen in respiration).

Sure things could evolve differently, but we would have no idea what compounds to even start looking for in space.

 

[Eumersian]

It could be because that's pretty much all we know. Life as we know it tends to be based around carbon. Though there is evidence of other possibilities (like this right here http://www.newscientist.com/article/dn19805-arsenicbased-bacteria-point-to-new-life-forms.html ) most of our research into the life sciences has been all about what we have here on our planet, which is carbon based, and seems to require water in order to thrive.

 

[Terracrete]

Okay I was strolling along minding my own business after watching some Zero Punctuation when I came across your question.

Water due to interactions between the 2 hydrogen protons of one water molecule being strongly attracted to the electrons of oxygen atoms of adjacent water molecules, hereby refereed to as hydrogen bonding gives water some very unusual properties that are critical to aiding in the development of life.

1. Water in solid form (ice) is less dense then the liquid form (water), this is the reverse the normal. Because of this ice floats in water (normally a solid material would sink when placed in to its liquid form.

1a. Because of the above property it is very difficult to freeze entire bulk body of water. As water deep below the surface is cooled, due to lack of exposure from the sun, it rises to the surface and heats up again where by it once again lowers back to the depths. This process is called convection.

2. Water is a universal solvent. Water can dissolve almost anything. This is critical for developing cellular structure, cellular structure requires interactions between charge particles such as potassium, chlorine, and sodium which water can enable by dissolving these charged salts into solution.

3. Water has strong capillarity properties. Capillary ability of a liquid to flow against gravity where liquid spontaneously rises in a narrow space such as a thin tube, or in porous materials such as paper or in some non-porous materials such as liquified carbon fiber. This allows water to reach the top of trees from the roots.

4. Based on the size of a water molecule it should be a gas at standard temperature and pressure, but due to hydrogen bonding it is a liquid. This is important because water's small size as a liquid allows it some special properties, such as osmosis.

There are many other unique properties of water which I wont' cover due to space limits and my not wanting to

 

[Terracrete]

I thought it was because of the higher electronegativity of the oxygen in the water making it such an extraordinarily great solvent compared to other H2X groups? Then some mumbo jumbo about needing an aqueous environment for efficient means of transport (it's been a while since I did this) required in living organisms...

This could be completely wrong, I didn't do too well in that semester but that's my say.

The electronegativity of oxygen is critical to the the formation of hydrogen bonding. The electron from each hydrogen is pulled toward the oxygen forming pseudo charges for the hydrogens and oxygen, from each hydrogen-oxygen intermolecular interactions are enabled.
It is also the small size of the hydrogen atoms and the abundance of hydrogen. Using only the electronegativity explanation it would appear that Fr2O would make the best possible solvent, however due to the bulky size of Fr, the interactions between lower orbital electrons and a very dense electron cloud, and the lack of naturally occurring Fr, Fr2O doesn't naturally exist.

 

[Siovar]

Things that live without oxygen are well known, and assumed to have developed before those that rely on oxygen since photosynthesis is pretty darn complex. They are called anaerobic life.

Oxygen is highly reactive and is actually poisonous to alot of this sort of life so when photosynthesis took off and started making alot of oxygen (think algae) as a waste material we actually had a big extinction event and aerobes took over

Ive heard about liquid methane or ammonia been a potential substitute for H2O on places like Titan but as far as im aware its only theoretical

 

[Princess Rose]

Why do we always assume that for the life to exist, the conditions on the planet have to be at least somewhat similar to those of earth?
More specifically the presence of liquid water.

Couldn't life come to existence and evolve in, let's say, a lake of sulfured acid....or even better a lake made out of some other element that we haven't discovered yet?

Also couldn't some life forms evolve in such a way that they breathe nitrogen or CO2 instead of oxygen?
Can life come to existence in a completely different environment?

Some basic reasons:

1) Because the only way we are SURE life can occur is in water. Because it did. Here. Some sci-fi authors have speculated about other possibilities (methane is a popular choice, as is silicon) but for carbon based life to occur it pretty much requires water.

2) You may have noticed I mentioned carbon, silicon, and methane above, yes? That's because all three have a structure suitable to life. Why those three? I have no idea. But I do know that there is scientific evidence as to why those are the three most likely chemicals to be the basis for life in the universe. Again, you probably want to ask a chemist about why that is.

3) Of course, the REAL reason for this in most sci-fi shows is the following: human actors.
Basically, if humans have to act as the aliens, then the aliens need to have some basic biological similarities to humans. Sure, the likelyhood that other intelligent life would be bipedal is extremely low (without some sort of lantern-hung explanation such as is given in both Star Trek and Mass Effect (that a mysterious race of Aliens did it)), but since the actors are bipedal, so must the aliens be. And, that being the case, it is most logical that they are carbon based too, and thus formed in a water-rich environment.

 

[Shirastro]

Okay I was strolling along minding my own business after watching some Zero Punctuation when I came across your question.

Water due to interactions between the 2 hydrogen protons of one water molecule being strongly attracted to the electrons of oxygen atoms of adjacent water molecules, hereby refereed to as hydrogen bonding gives water some very unusual properties that are critical to aiding in the development of life.

1. Water in solid form (ice) is less dense then the liquid form (water), this is the reverse the normal. Because of this ice floats in water (normally a solid material would sink when placed in to its liquid form.

1a. Because of the above property it is very difficult to freeze entire bulk body of water. As water deep below the surface is cooled, due to lack of exposure from the sun, it rises to the surface and heats up again where by it once again lowers back to the depths. This process is called convection.

2. Water is a universal solvent. Water can dissolve almost anything. This is critical for developing cellular structure, cellular structure requires interactions between charge particles such as potassium, chlorine, and sodium which water can enable by dissolving these charged salts into solution.

3. Water has strong capillarity properties. Capillary ability of a liquid to flow against gravity where liquid spontaneously rises in a narrow space such as a thin tube, or in porous materials such as paper or in some non-porous materials such as liquified carbon fiber. This allows water to reach the top of trees from the roots.

4. Based on the size of a water molecule it should be a gas at standard temperature and pressure, but due to hydrogen bonding it is a liquid. This is important because water's small size as a liquid allows it some special properties, such as osmosis.

There are many other unique properties of water which I wont' cover due to space limits and my not wanting to

Wow i actually understood most of what you said here, great explanation

A side question though! Is it absolutely impossible for life to form without water than?

 

[Shirastro]

Why do we always assume that for the life to exist, the conditions on the planet have to be at least somewhat similar to those of earth?
More specifically the presence of liquid water.

Couldn't life come to existence and evolve in, let's say, a lake of sulfured acid....or even better a lake made out of some other element that we haven't discovered yet?

Also couldn't some life forms evolve in such a way that they breathe nitrogen or CO2 instead of oxygen?
Can life come to existence in a completely different environment?

Some basic reasons:

1) Because the only way we are SURE life can occur is in water. Because it did. Here. Some sci-fi authors have speculated about other possibilities (methane is a popular choice, as is silicon) but for carbon based life to occur it pretty much requires water.

2) You may have noticed I mentioned carbon, silicon, and methane above, yes? That's because all three have a structure suitable to life. Why those three? I have no idea. But I do know that there is scientific evidence as to why those are the three most likely chemicals to be the basis for life in the universe. Again, you probably want to ask a chemist about why that is.

3) Of course, the REAL reason for this in most sci-fi shows is the following: human actors.
Basically, if humans have to act as the aliens, then the aliens need to have some basic biological similarities to humans. Sure, the likelyhood that other intelligent life would be bipedal is extremely low (without some sort of lantern-hung explanation such as is given in both Star Trek and Mass Effect (that a mysterious race of Aliens did it)), but since the actors are bipedal, so must the aliens be. And, that being the case, it is most logical that they are carbon based too, and thus formed in a water-rich environment.

Now that you mentioned star trek and silicon based life you reminded me of Odo from derp space 9

 

[Nerdstar]

as its already been said there are alternate possibilities for life besides your run of the mill carbon based life, water is thought to be needed because it allows organic compounds to react in ways that ultimately allow replication, is considered a universal solvent, and is necessary for both photosynthesis and respiration.

chemosynthesis can be used to convert carbon molecules into organic matter using oxidation, in fact its theorised that possible alien life in the form of bacteria or a jellyfish analogue would use such a method to survive on europa

 

[Terracrete]

Also couldn't some life forms evolve in such a way that they breathe nitrogen or CO2 instead of oxygen?
Can life come to existence in a completely different environment?

Believe it or not oxygen that is to say the gas O2 is a very destructive molecule. Oxygen is an excellent oxidation agent (a molecule that oxidizes or causes other molecules to give up electrons and takes up the removed electron itself).

The significance of this is energy. Oxidation reduction reactions are ways in which energy can be stored or given off.

Example a lead battery using oxidation-reduction with an acid/base.
Example oxygen + a hydrocarbon + a small activation energy is the bases for fire, energy is removed from the stored bonds in the hydrocarbon in the form of heat and light.

While destructive it is also vital to cellular respiration. Cells must exert stored energy to complete tasks such as cellular reproduction, moving necessary ions/salts of potassium, chlorine, and sodium from one side of the cellular wall to the other where it is needed, creating proteins necessary for bodily functions, etc.

Think of it this way...
The only true source of biological energy is the sun
This energy is collected and stored in green plants
Plants are consumed either them selves or indirectly via eating other things that ate the plants.
Hydrocarbons (IE "Carbs") are a storage unit of energy
The body needs a way to release the energy for use
Oxygen + Hydrocarbon fuel source + activation energy

In biological chemistry this gets rather complex, but is generally refered to as either the Kreb Cycle or the Citric acid cycle.

 

[Nerdstar]

Why do we always assume that for the life to exist, the conditions on the planet have to be at least somewhat similar to those of earth?
More specifically the presence of liquid water.

Couldn't life come to existence and evolve in, let's say, a lake of sulfured acid....or even better a lake made out of some other element that we haven't discovered yet?

Also couldn't some life forms evolve in such a way that they breathe nitrogen or CO2 instead of oxygen?
Can life come to existence in a completely different environment?

Some basic reasons:

1) Because the only way we are SURE life can occur is in water. Because it did. Here. Some sci-fi authors have speculated about other possibilities (methane is a popular choice, as is silicon) but for carbon based life to occur it pretty much requires water.

2) You may have noticed I mentioned carbon, silicon, and methane above, yes? That's because all three have a structure suitable to life. Why those three? I have no idea. But I do know that there is scientific evidence as to why those are the three most likely chemicals to be the basis for life in the universe. Again, you probably want to ask a chemist about why that is.

3) Of course, the REAL reason for this in most sci-fi shows is the following: human actors.
Basically, if humans have to act as the aliens, then the aliens need to have some basic biological similarities to humans. Sure, the likelyhood that other intelligent life would be bipedal is extremely low (without some sort of lantern-hung explanation such as is given in both Star Trek and Mass Effect (that a mysterious race of Aliens did it)), but since the actors are bipedal, so must the aliens be. And, that being the case, it is most logical that they are carbon based too, and thus formed in a water-rich environment.

Now that you mentioned star trek and silicon based life you reminded me of Odo from dep space 9

hypothetically, no, water is not needed. heres a link to wikipedia that proposes some alternate theories on some non-water based biochemistry . GFAJ-1 showed promise that such life could possiably devlop

http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

 

[Terracrete]

A side question though! Is it absolutely impossible for life to form without water than?

To answer this question I pose the following facts:

1. There are four phases of matter, and of these four solid and plasma are not life conducive.

2. For the early stages of life development (IE. before the development of an enclose cellular structure when all the internal interactions of a cell are completely exposed to the environment) a protective environment is needed to prevent dangerous oxidation from a nearby O2 gas source (which as mentioned above is critical to energy storage and usage of the cell).

3. As demonstrated in the Miller and Urey experiment, a high energy source is required for the initial creation of amino acids which are critical to the development of proteins.

Based on just these few facts, and utilizing process of elimination we are left with the following.

The original environment for the creation of life must be either aqueous or gaseous, non-oxidizing/reductive, and stable when exposed to high energy sources.

This rules out methane (explosive)
Leaving your two remaining selections CO2 and H2O...

CO2 is an acidic oxide and in addition is not a very good solvent. All the different amino acids once created need to be able to mix and collide so as to create proteins.

This makes water the most viable choice. (Of course there are several other reasons why as well)

 

[Nerdstar]

A side question though! Is it absolutely impossible for life to form without water than?

To answer this question I pose the following facts:

1. There are four phases of matter, and of these four solid and plasma are not life conducive.

2. For the early stages of life development (IE. before the development of an enclose cellular structure when all the internal interactions of a cell are completely exposed to the environment) a protective environment is needed to prevent dangerous oxidation from a nearby O2 gas source (which as mentioned above is critical to energy storage and usage of the cell).

3. As demonstrated in the Miller and Urey experiment, a high energy source is required for the initial creation of amino acids which are critical to the development of proteins.

Based on just these few facts, and utilizing process of elimination we are left with the following.

The original environment for the creation of life must be either aqueous or gaseous, non-oxidizing/reductive, and stable when exposed to high energy sources.

This rules out methane (explosive)
Leaving your two remaining selections CO2 and H2O...

CO2 is an acidic oxide and in addition is not a very good solvent. All the different amino acids once created need to be able to mix and collide so as to create proteins.

This makes water the most viable choice. (Of course there are several other reasons why as well)

ah! but what about Ammonia, it can be both aqueous or gaseous, non-oxidizing/reductive (in the proper reducing envorment), and stable when exposed to high energy sources(showen in the Miller?Urey experiment).

 

[Terracrete]

ah! but what about Ammonia, it can be both aqueous or gaseous, non-oxidizing/reductive (in the proper reducing envorment), and stable when exposed to high energy sources(showen in the Miller?Urey experiment).

Short answer is that Ammonia is immersible with O2, which is highly destructive to new forming life.