Though we all know what is life, it is a challenge for scientists and philosophers to define life in unequivocal terms. This is difficult partly because life is a process, not a pure substance.  Any definition of life must be sufficiently broad to encompass all life with which we are familiar, and must be sufficiently general to include life that may be fundamentally different from life on Earth.




Biology – Seven characteristics of life

 “We biologists have a working definition: 'something organic that can obtain energy, independently reproduce and have the ability to adapt to its environment.'” FSU  Biology Professor Dr. Scott  Fritz.

Life is considered a characteristic of organisms that exhibit all or most of the following characteristics or traits:

1.       Homeostasis: Regulation of the internal environment to maintain a constant state; for example, electrolyte concentration or sweating to reduce temperature.

2.       Organization: Being structurally composed of one or more cells — the basic units of life.

3.       Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.

4.       Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.

5.       Adaptation: The ability to change over time in response to the environment. This ability is fundamental to the process of evolution and is determined by the organism's heredity, diet, and external factors.

6.       Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multi cellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemo taxis.

7.       Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms.

These complex processes, called physiological functions, have underlying physical and chemical bases, as well as signaling and control mechanisms that are essential to maintaining life.



http://infohost.nmt.edu/~klathrop/7characterisitcs_of_life.htm gives this interesting list


The 7 Characteristics of Life:

 1. Living Things are composed of Cells:


  • Single-cell organisms have everything they need to be self-sufficient.
  • In multi-cellular organisms, specialization increases until some cells do only certain things.

2. Living Things Have Different Levels of Organization:

  • Both molecular and cellular organization.
  • Living things must be able to organize simple substances into complex ones.
  • Living things organize cells at several levels: 
     Tissue - a group of cells that perform a common function.

Organ - a group of tissues that perform a common function.

Organ system - a group of organs that perform a common function.

Organism - any complete living thing.


levels of cellular organization

3. Living Things Use Energy: 

  • Living things take in energy and use it for maintenance and growth

4. Living Things Respond To Their Environment:

  • Living things will make changes in response to a stimulus in their environment.
  • A behavior is a complex set of responses.

  5. Living Things Grow: 

  • Cell division - the orderly formation of new cells.
  • Cell enlargement - the increase in size of a cell. Cells grow to a certain size and then divide.
  • An organism gets larger as the number of its cells increases.

6. Living Things Reproduce: 

  • Reproduction is not essential for the survival of individual organisms, but must occur for a species to survive.
  • All living things reproduce in one of the following ways:
    • Asexual reproduction - Producing offspring without the use of gametes.
    • Sexual reproduction - Producing offspring by the joining of sex cells.

7. Living Things Adapt To Their Environment:

  • Adaptations are traits giving an organism an advantage in a certain environment.
  • Variation of individuals is important for a healthy species.

With each new technological breakthrough things get more complicated. Microscopes become successively more powerful, able to penetrate the depths of body, cell and nucleus, revealing new life, different life, unclassifiable by common convention.



Carbon-based life


The Lewis structure of a carbon atom, showing its four valence electrons.

For some unknown reason, Carbon forms the key component for all known naturally occurring life on Earth. Complex molecules are made up of carbon bonded with other elements, especially oxygen, hydrogen and nitrogen, and carbon is able to bond with all of these because of its four valence electrons. The complex molecules that humans use in their biological processes are based primarily on chains of carbon atoms (with some other atoms thrown in). Every biologically active molecule used in the human body contains carbon somewhere. Other elements used by the human body include oxygen, nitrogen, hydrogen, sulfur, phosphorus, sodium, potassium and calcium, but these elements are only attached to the carbon chains.  

Carbon is abundant on earth. It is also lightweight and relatively small in size, making it easier for enzymes to manipulate carbon molecules. It is often assumed in astrobiology that if life exists somewhere else in the universe, it will also be carbon based.  This assumption is referred to by critics as carbon chauvinism.

Characteristics of carbon as a basis for life

The two most important characteristics of carbon as a basis for the chemistry of life are that it has four valence bonds and that the energy required making or breaking a bond is just at an appropriate level for building molecules which are not only stable, but also reactive.

The fact that carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long complex molecules and polymers.

There are not many other elements which even appear to be promising candidates for supporting life - for example, processes such as metabolism - but the most frequently suggested alternative is silicon. This is in the same group in the Periodic Table of elements and therefore also has four valence bonds. It also bonds to itself, but generally in the form of crystal lattices rather than long chains. Silicon compounds are generally stable but do not support the ability readily to re-combine in different permutations in a manner that would plausibly support lifelike processes.

The acronym CHNOPS, which stands for carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, represents the six most important chemical elements whose covalent combinations make up most biological molecules on Earth.  Sulfur is used in the amino acids cysteine and methionine.  Phosphorus is an essential element in the formation of phospholipids, a class of lipids that are a major component of all cell membranes, as they can form lipid bilayers, which keep ions, proteins, and other molecules where they are needed for cell function, and prevent them from diffusing into areas where they should not be. Phospholipids are also an essential component of nucleic acids.


Living things contain DNA

The seven characteristics are simply explanation of what is observed in all Life forms.  However a better definition of Life is in terms of the DNA codes that are found in all life forms.  Every living thing has in their cells the instructions, the blueprint of life.  This is the DNA or deoxyribonucleic acid found in our cell nucleus.  The genetic instructions of all living organisms are contained in molecules of deoxyribonucleic acid. DNA contains instructions that are used by cells to produce proteins. The vast array of different chemical reactions that build and maintain cells are controlled by proteins.  DNA is made of a series of bases in a specific order.  Cells use DNA to create amino acids which in turn create proteins, which in turn create cells, which in turn create body parts over a lot of intermediate steps.

The DNA is double helix shaped, which is a “twisted ladder” shape.  Each rung of the ladder is made of a series of two bases bonded together.   DNA has four bases called: Adenine, Thymine, Cytosine, Guanine, which we shorten to A, T, C, G.   A always binds to T, C always binds to G.  The way that these bases sit on each rung of the ladder determine the order they will code for proteins.  The DNA will split apart when it is time to use the DNA for coding.  Each rung of the ladder is available to bind to other bases called RNA. 

The instructions for making proteins are found in the genes; different genes contain instructions for different proteins or parts of proteins. Before protein is synthesized, the information in DNA must first be copied. The copy is composed of a substance similar to DNA called mRNA (for messenger RNA). It is mRNA that is used in the manufacture of protein. The diagram below illustrates that information in DNA is used to create mRNA and that information in mRNA is used to synthesize protein.  

By 1950’s, DNA was pinned down as the genetic blueprint of life.   Stanley Miller was taught that life was produced from organic compounds under earth's  atmospheric conditions of around 3,800 million years ago when high voltage electric lightning charges  hit on a mixture of  hydrogen, methane, ammonia and water vapor soup. He tried to reproduce these conditions.  Lo and behold, there appears - amino acids, commonly called the building blocks of life. Subsequent experiments in this new field of “abiotic chemistry” would yield purine and pyrimidine, sugars which are integral to the structure of both RNA and DNA.  Thus we came to the beautiful conclusion that life’s organic components could be synthesized from an inorganic matter. The chemical compounds of living things are known as organic compounds because of their association with organisms. They do not produce life?  How do you go from organic compounds to organisms with life? How do the components of life rise up and coalesce into an organism?” The question is how to jump from matter to life is gulf which science could not surf.


Where do these come from?

It is the code

Key carbon-based molecules in the life processes are:

The most notable groups of chemicals used in the processes of living organisms include:

Proteins, which are the building blocks from which the structures of living organisms are constructed (this includes almost all enzymes, which catalyses organic chemical reactions)

Nucleic acids, which carry genetic information

Carbohydrates, which store energy in a form that can be used by living cells

Lipids,  which also store energy, but in a more concentrated form, and which may be stored for extended periods in the bodies of animals.

As is clear, carbon is not the most abundant material in the universe nor of the surface of earth to form the most probable building block for life.  Yet it is the basic element that supports life - a low probability event.


Life Outside of Earth

Alien life, such as bacteria, has been hypothesized to exist in the Solar System and throughout the universe. This hypothesis relies on the vast size and consistent physical laws of the observable universe. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere other than Earth.

Enrico Fermi’s paradox: at lunch one day in 1950, the famous physicist asked aloud, ‘Where is everybody?’ referring to alien visitors. Fermi argued that if the Earth is not special in having intelligent life, then civilizations should already have evolved many times in our galaxy, since there are billions of stars older than the Sun. If any one of these civilizations had wanted to colonize the galaxy, they could have done so by now. Since there is no compelling evidence that any aliens have visited the Earth, we must conclude that we are alone.

On the other hand, one of the pioneers of the search for extraterrestrial intelligence, Frank Drake, estimated that there were probably between 1000 and 100 million advanced civilizations in our galaxy. 





Dr. Frank Drake (1930- )

Drake equation, also called Green Bank equation purports to yield the number N of technically advanced civilizations in the Milky Way Galaxy as a function of other astronomical, biological, and psychological factors. Formulated in large part by the U.S. astrophysicist Frank Drake, it was first discussed in 1961 at a conference on the “search for extraterrestrial intelligence” (SETI), held at the National Radio Astronomy Observatory in Green Bank, W.Va. The equation predicts the number of possible life forms in the Galaxy.

. File:White House position on ET.png

The official U.S. government position on extraterrestrial life, and the three major efforts in the search for it are:
1. Looking for 
extra solar planets (Image: Kepler spacecraft)
Listening for signals (Image: Allen array)
Robotic exploration of the Solar System (Image: Curiosity rover)

The Search for Extra-Terrestrial Intelligence (SETI)

The Search for Extra-Terrestrial Intelligence (SETI) is based at the University of California in Berkley and has several radio telescopes that are dedicated to listening out for signals from alternative life forms. The researchers need to be dedicated since despite constant searching after picking up a promising signal in 1977, they haven’t heard anything else.

As scientists add to the growing list of planets in the universe which are classed as habitable, Professor Cockell poses an important question – Does life always arise whenever a planet's conditions deem it possible? It should if life evolved whenever physical conditions are met. Habitable planets may turn out to be abundant in the universe; however the search for life on them may yield only negative results.

This could mean that:

1. No life could evolve outside of earth

2.  If they did these never reached a civilization which could technologically advanced to send out signals to the rest of the cosmos.

3.  These civilizations which reached a technologically advanced state, did not survive beyond at least a hundred years after that.  They have destroyed themselves with atomic and nuclear power.  They were a fallen people and there were no Noah who survived and continued.

"It is dangerous to assume life is common across the universe – it encourages people to think that not finding signs of life is a "failure" when in fact it would tell us a lot about the origins of life," added Professor Cockell. In his talk, Professor Cockell suggests that scientists should use his hypothesis to avoid the assumption that habitable conditions are likely to contain life, and as a result, approach the question in a more scientifically robust and experimentally testable way.” (Read more at: http://phys.org/news/2013-03-life.html#jCp). 


Thus, as far as we know, life did not and does not evolve because the conditions are favorable.  Habitable planets may turn out to be abundant in the universe; however the search for life on them may yield many negative results. "It is dangerous to assume life is common across the universe – it encourages people to think that not finding signs of life is a "failure" when in fact it would tell us a lot about the origins of life," added Professor Cockell.

In his talk, Professor Cockell suggests that scientists should use his hypothesis to avoid the assumption that habitable conditions are likely to contain life, and as a result, approach the question in a more scientifically robust and experimentally testable way.

(Read more at: http://phys.org/news/2013-03-life.html#jCp)

No experiment has produced life from chemicals, and it has never been observed.  Biochemists have not been able to create a single cell or any simple form of life from raw chemicals even though we have been at it.  Growing awareness of the extreme complexity of living things at even the smallest scales led to the formal challenge of Evolution theory by the only possible alternative which demanded an Intelligent Design by a Person. From this perspective, no amount of time, even billions of years, would produce the biosphere by natural causes alone.

“Robert Shapiro is a Professor of chemistry and DNA expert at New York University. A Darwinist, Shapiro calculated the probability of the 2,000 different proteins found in simple bacteria having formed coincidentally.  He obtained the following result: 1 in 10^40,000 (a number formed by 4,000 zeros following the number 1; which does not correspond to anything in the universe). And there are 200,000 different proteins in the human body!  The chance of the 2,000 proteins in simple bacteria to form coincidentally is 1 in 1040,000. Since the number of different proteins in the human body is 200,000, nothing can put this improbability into perspective.

Chandra Wickramasinghe, Professor of Applied Mathematics and Astronomy at Cardiff University, has this to say about Shapiro’s calculation:

“The likelihood of the spontaneous formation of life from inanimate matter is one to a number with 10^40,000 noughts after it…It is big enough to bury Darwin and the whole theory of evolution. There was no primeval soup, neither on this planet nor on any other, and if the beginnings of life were not random, they must therefore have been the product of purposeful intelligence.””
A Chain of Miracles, Harun Yahya  



The fact which should strike any scientist is that life does not evolve because the conditions are favorable for life.  Life is not a potential property of matter.  Life came from dimensions outside of the 11 dimensional material realms. It penetrates beyond the uncertainty region and beyond the singularity of creation. Life was given by an intelligent creator from the dimension of life. ”Thus, in our view, a ‘proto-conscious’ source of mind is omnipresent in the universe as OR events which shape reality. However experientially rich, human-like consciousness required biological evolution of a mechanism to ‘orchestrate’ Objective Reduction events, and couple them to brain neuronal activity." S. Hameroff, R. Penrose / Physics of Life Reviews

Evidently at some point in history, the life giving Spirit entered into the realm of Matter to produce life as we see on earth.  Is it still present in the whole Universe?  Did it create other forms of life in other dimensions which are beyond matter also?  It did.  That is what the Bible asserts.

In creation, God the Father is the ultimate intelligent Designer (far beyond any level of intelligence we could ever imagine) of the universe. Everything was built according to a plan conceived in His mind. The universe was then spoken into existence by God the Son - (John 1).  The Word was made flesh in the creation of the material Universe. The thoughts of God were put into the form of spoken words and from the words of the Son of God; the creation sprang into existence and took on form and shape.

The universe was empowered, molded and crafted, and inanimate cells were given life by God the Holy Spirit.


Thus, God did not order the universe into existence as a finished and complete system where there is no future and hope.   The creation involved the cooperative work of all three persons of the godhead. The Biblical view of God is that of a "hands-on" creation. God was involved in every step of the design, fabrication and finishing of the universe, with all the potential of free independent development and growth. He remains involved to this day as the Sustainer of everything (Col. 1:16, 17).  In the same tone God involves all his creation to be involved in the process of growth and future.






Maxwell’s Demon
creating order from disorder



Life in Other Dimensions


However, we are here talking only about the life as we know of based on Carbon and in Material Realm.  Are there other life forms in non-material realms?  Have anything in common with us here and now?  Can we come in communication with them?  These are not matters usually dealt with in science.  It is taken over by religions, philosophy and mysticism.  All cultures in the world from time immemorial had asserted such existence of life and called them in generic terms as Spirits.  They co-exist with material world and they do share some dimension with us to communicate with us.  Thus the cosmos is much bigger than we ever can understand.  What is given in folklores and scriptures form only a skeleton of the reality.