[kenhikage (OP)]

Can anyone define life in such a way that excludes crystals?

If not, why aren't crystals considered living things?

[Soul Surfer]

Life is anything that uses the materials and energy flow within its environment to have a stable, controlled and self replicating existence.  During this process it will take in materials and energy as food and excrete waste products.  It is also essential that a life form is capable of self replication even if it does this via different intermediate stages  for example   caterpillar > pupa > butterfly > egg > caterpillar .

This process clearly excludes crystals which are merely an ordered and more stable state formed by solid materials in response to the geometrical shape and bonding processes in their molecules although the presence of a crystal may seed a growing crystal it can do nothing else and crystals can form spontaneously in the absence of a seed  it therefore has no similarities with life whatever.

[kenhikage (OP)]

Life is anything that uses the materials and energy flow within its environment to have a stable, controlled and self replicating existence.

Don't crystals use matter and/or heat from their environments to grow? And, isn't crystal replication similar to the replication of fungi and molds.

This process clearly excludes crystals which are merely an ordered and more stable state formed by solid materials in response to the geometrical shape and bonding processes in their molecules

How is that different from cellular respiration?

crystals can form spontaneously in the absence of a seed

How is that different from abiogenesis?

I'm not trying to be a jerk. Obviously I know that crystals are inherently different from organic matter. But, I'd like to see the words which differentiate the two, not just have a feeling.

[syhprum]

I would define life as the possession of genetic materiel which gives the possibility of evolution.
I know of no way crystals can be said to evolve.

[kenhikage (OP)]

Yeah, that's a pretty satisfactory summation.

Let's challenge it just for fun.
Viruses?
Human beings have more nonhuman DNA in and on us than we do our own. If we were completely stripped of everything not in our genetic code, we wouldn't last a few moments. That is, we aren't alive with only our DNA.

[Soul Surfer]

I agree that I should have added the possibility of change and evolution to my original definition but it was clear that crystals do not possess this possibility and I considered the basics sufficient.   Viruses need other self replicating cells to replicate but probably evolved alongside the most basic lifeforms and as you say ate incorporated into complex genomes

[kenhikage (OP)]

And besides viruses, we depend on multitudes of single celled organisms and mitocondria to live. Without them we wouldn't have "life." So, it also seems that interdependence should play a role in the definition, don't you agree.

I'm not sure that keeps out crystals. I must admit I don't know much about them. It just seems to me that they aren't considered life, because they don't seem (feel) like life to us.

[Soul Surfer]

I agree that the interdependent complexities of life are far from fully understood.

I am not sure why you have this thing about crystals they are just geometric arrangements of molecules most of which take up the lowest energy shape. they may be pretty but they have no dynamism. 

molecules involved with life can crystallise but it is the molecule not the crystal that is important.  X ray crystallography was the technique used to work out the structure of DNA.

[kenhikage (OP)]

I am not sure why you have this thing about crystals they are just geometric arrangements of molecules most of which take up the lowest energy shape. they may be pretty but they have no dynamism.

Well, DNA is also a geometric arrangement of molecules. Life takes in energy and turns that into reproduction and waste. I don't see the differences on a fundamental level.

[Soul Surfer]

Yes I agree that is all DNA is.  In the absence of the replication machines that exist in a cell it is nothing more than a molecule that can be crystallised.  OK it contains all the information needed to make the cell and its replication machines and also then how to go on to put cells together to create an organism but in the absence of the cell it is no more use than a set of drawings in a cupboard without the machine shop and materials needed to build the aircraft. it is inanimate and not alive just like the crystal.

In order to fully create life in a lab it not just sufficient to create the DNA of a living thing it is essential to put it into a fully functional cell which is a far more complex thing to build in a lab.  OK most experimenters today just hijack a cell that some other living thing has built for its own use.

[kenhikage (OP)]

Great point. Life on Earth requires a cell (and some proteins and such) to convert things into food, energy, and new cells.

The reason I asked is because I believe we will find things on other planets that will be difficult to categorize as life or not. Viruses are a great example. If we found them on an alien world wouldn't we say life has been found? I'm sure there will be other things that we haven't even imagined that will be sticky points. So I wanted to know, what is definitely out of bounds with what we currently know.

[zhangluo]

Yes I agree that the interdependent complexities of life are far from fully understood.too newbielink:http://www.magnets-fasts.com/ [nonactive],But There is always some different