Biological Classification: Kingdom Animalia

Origin of life: Even the oldest human observation (like the Rig Vedic period of India) recorded in history, supports the thought that most primordial life forms might have began in water only.
(reference: pictures 1, 2 & 3 of a hymn from Rig Veda shown are in old Sanskrit language text translated in Hindi & English).

Later Miller-Urey experiment (1952-53) and Oparin proved it so in laboratory conditions for the modern mind.
Primordial Soup: This first life form, sort of naked protoplasm kind of thing took the shape, which was named Cell by Robert Hooke (1665) and life began to grow and took a route of simple to complex forms, towards two major branches, as animal and plant cell.
(reference: picture 4, 5 & 6).

Need of Classification: As number of life forms were in millions with much variety, a need arose to name and classify them. As we all know the credit goes to Carolus Linnæus a Swedish botanist, physician, and zoologist, father of modern taxonomy. Credit for Binomial nomenclature also goes to Linnæus. The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Botanical Nomenclature (ICBN) for plants.
(reference picture: 7, 8 & 9)

System of Classification and their Units: All the types of classifications proposed & followed from Linnaeus (1735) to Cavalier-Smith (2004) follow almost the same domain name of units as: Kingdom-Phylum-Class-Order-Family-Genus-Species.
(reference picture: 11, 12 & 13)

Interesting Evolutionary Trend: The classification patterns followed is so interesting that this itself is an Evidence in the support of Darwin's theory of Organic Evolution.
As we move from base of the classification, we find the life forms they them self are arranged in simpler to complex forms like: Unicellular Prokaryote-Unicellular Eukaryote- Multicellular Tissue level- Multicellular organ level- Multicellular Organ System level.
(reference picture: 14)

Oxygen: A Necessary Evil

Inorganic Evolution:

Astrophysics/Particle Physics states that the journey of existence started from Plasma state of matter to sub-atomic particle to the atom of lowest atomic number (say one proton & one electron, i.e. Hydrogen).

Then it was the turn of inorganic evolution, gradually atoms of higher atomic number came into existence .... elements formed, and then their compounds ....

(reference: picture #1)

Inorganic Evolution Evident:

This is evident from the periodic table of chemical elements (1896 Dimitri Mendeleev) in which the elements are arranged by order of atomic number in such a way that the periodic properties ( chemical periodicity) of the elements are made clear.

In 1914 Rutherford .... transmuted a Nitrogen atom into an Oxygen atom for the first time.

Organic Evolution:

When 'Primordial Soup' ( no Nucleus, no Cell Membrane as such) of some simple organic compounds gained just few characteristics of life (nutrition as growing in size and reproduction as dividing into two), .... in the environment of Hydrogen (as Oxygen was not found). It was all a reducing environment ( opposite to oxidizing of Oxygen).

(reference: picture #3)

Age-Old 'Vedic' Observation (from India):

One of the oldest recorded human observation is made evident in the book 'Rig Veda' ( 5-6 thousand years BC) about the nature of these primordial life forms and their reducing environment.

(reference: picture #2)

Oxygen:

In the further course of inorganic evolution, oxygen came to exist and the whole scenario of organic evolution changed... as oxygen being highly reactive.. due to oxidizing behavior (having only 2 electrons in outermost orbit, it has great binding affinity with all); and soon primitive life forms learned to live with this unwanted oxidizing guest of their environment by burning ( getting oxidized) some part of their cellular body to get rid of it.

They gradually developed some organelle , later to Mitochondria in their cell and stored those emitted energy in molecular form (ATP) for later use for their further biological activity.

That was the beginning of an environment of oxidative respiration, that is what we have today, changing the the course of life development of the life forms there on ....

(reference: picture #4,5,6,7)

Conclusion:

Oxygen is not a friend. It oxidizes, burns the part of cell...or rather silently a killer factor..
But ever since through our evolutionary history, life forms have adopted to this evil factor..

Related blog post links:

http://sciencedoing.blogspot.in/2013/05/oxidative-stress-strain-as-predisposing.html
http://sciencedoing.blogspot.in/2013/05/dark-oxidants-super-oxides-in-depth-of.html

http://sciencedoing.blogspot.in/2012/09/free-radicals-cause-and-concern.html

Origin Of Life: Metaphysics

* How the Universe came to exist from nothing, much before the earth was born and the lives were made there in....??

** we have a lot many scientific theories and explanations for the above thought in last 200 years of the quest of human mind..

*** But looking back in time of human history of it's Metaphysical approach to the problem, it's so interesting to see two references, one, a very old in the memory of Human history: The "Vedas" ( "Hindus" ) and the other, the very recent of our time: The "Baha'i Faith";

1. The "Vedas" (treasured scriptures of "Hindus" in India) are perhaps the oldest written text on our planet today. They date back to the beginning of Indian civilization and are the earliest literary record of the whole Aryan race. They are supposed to have been passed through oral tradition for over 100,000 years. They came to us in written form between 4-6,000 years ago.

2. The "Bahai Faith" is the latest manifestation of God, in prophetic series on this earth, only 168 years old

3. Just go through these two streams of compilations and give a flight to your imagination without any reservation. For sure it's going to amaze you with a new Metaphysical perspective of 'Origin Of Life' ( and who knows, may be a new research paper of your own to put forward a new idea on the 'Cosmos & Life: with a Metaphysical touch' )!!

# There was neither the non-existent nor was the existent then; there was neither the region nor the sky that is above. What did cover it? Where, in whose protection? Was there water, unfathomable, deep? (ref:Rig Veda,Nasdiya.1)

# There was neither death, nor immortality. There was not the distinct knowledge of night and day. That one breathed without wind by its will power. Other than that there was nothing beyond. (ref:Rig Veda,Nasdiya.2)

# The darkness was concealed with darkness in the beginning. All this (world) was indistinguishable water. That which existed was covered with all pervading void; through the power of austerity that one was born. (ref:Rig Veda,Nasdiya.3)

# Desire, that was the first seed of the mind came upon that in the beginning. The sages, having searched in their heart with wisdom, found out the bond of existent in the non-existent. (ref:Rig Veda,Nasdiya.4)

# Their (web of effects which) was extended like the ray of the sun, was it cross? or was it below? or was it above? There were impregnators, there were great forces; food was below, and consumers (were) above. (ref:Rig Veda,Nasdiya.5)

# Who knows truly? Who shall here proclaim whence it is born? Whence it's vivid creation? Gods are later by the creation of this universe. Then who knows whence it has come in to being? (ref:Rig Veda,Nasdiya.6)

# Whence this vivid creation has come into being; either he held itor if he did not (then who held it?). He who is the lord of this (creation) is in the highest heaven; certainly he knows it; or if he does not know (then who knows?). (ref:Rig Veda,Nasdiya.7)

# O My Friends !
Have ye forgotten that true and radiant morn, when in those hallowed and blessed surroundings ye were all gathered in My presence beneath the shade of the tree of life, which is planted in the all-glorious paradise? Awe-struck ye listened as I gave utterance to these three most holy words: O friends! Prefer not your will to Mine, never desire that which I have not desired for yo, and approach Me not with lifeless hearts, defiled with worldly desires and cravings. Would ye but sanctify your souls, ye would at this present hour recall that place and those surroundings, and the truth of My utterance should be made evident unto all of you. (ref;Baha'i writings, Hidden Words of Baha'u'llah)

Notes:
* picture from top to down: Map of Vedic India, Vedas & Indian scriptures, Vedas manuscript, oral tradition of Vedas and a Baha'i shrine.
** Vedic translations were used of the authorities on the subject like; Sayana, Griffith, Macdonell, Wilson, Yaska, Max Muller, J. Muir, Roth, Benfey, Peterson.