As far as known life occurs only on earth through there is possibility of its presence elsewhere as well.
The oldest rocks on earth are dated as 4.3 billion years old. Rocks are of 3.9 billion years old age show presence of carbonates. Scientists believe them to be products of life activities.
The oldest fossils discovered are 3.3 to 3.5 billion years old. These fossils are of blue – green algae. |
Theory of special creation : |
- Such theories believe that some special power has created various kinds of organisms.
- Various religious thinkers explain origin of life in different ways.
- No evidence is provided.
- They are based on faith only.
- It believes that god created every thing including first man (Adam/Manu) and first woman (Eve/Shradha).
- No scientific basic.
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Theory of Abiogenesis : |
- It is also called Theory of spontaneous generation or Autobiogenesis.
- It believes that life must have originated from inanimate matter. Organisms can be formed from nonliving things like mud, dung, rain etc.
- Worms are produced in dung.
- Earth worms develop from soil.
- Files develop from meat.
- All such beliefs were of this kind.
- Later they were proved that even microorganisms arise from pre-existing micro-organisms only.
- Pasteur proved that even micro-organisms arise from pre-existing microorganisms only.
- Nobody now accepts this theory.
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Cosmic origin (Meteorite Theory) : |
- Life came on earth some other planet.
- Such principles believe that at its time of origin or at some later time, life might have come to earth through meteors.
- This belief is also not required.
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Origin of life from Inanimate Matter on Earth:
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Primitive life must have come into existence through various chemical reactions between materials present
on earth. This belief is a kind of abiogenesis principle.
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Origin of Earth : |
Origin of life is limited with the origin of earth. Our universe came existence some 15 billion years ago.
Our solar system was formed some 4.5 billion years ago. With the passage of time, planets became separated
from the sun. Our earth is also one such planet. |
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Development of favorable conditions for origin of life : |
- The earth was in its solid phase.
- Its surface was surrounding by a gaseous envelop called as lithosphere.
- Later the liquid phase appeared, where the earth temperature fell down 100° C.
- In the crust of earth different element were present. Such as sulphur, phosphorus, magnesium.
- In the core of earth, are collected substances like iron and nickel.
- The gaseous envelop contained carbon, helium, hydrogen, nitrogen and oxygen.
- With a gradual cooling of earth, conditions favourable for origin of life were created.
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Oparin and Haldane Hypothesis : |
- The Russian scientist, Oparin and the British scientist Haldane proposed an explanation to explain the origin of life.
- It is the modern naturalistic, physicochemical or chemical theory of life.
- It is also called theory of protobiogenesis.
- They believe that primitive life originated from inanimate matter in the primitive environment of earth.
- Millions of years have passed in this process.
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Primitive Environment on earth : |
Free oxygen was almost absent in the primitive atmosphere. Oxygen occurred as a constitute in water and as a bound component in metallic salts. The entire atmosphere was a reducing one. That′s why if an organic molecule were formed, it would not be decomposed.
Moreover, there was no ozone, so no filtration of ultra violet radiations.
There was a high concentration of hydrogen in the atmosphere. It occurred mainly as methane (CH4), ammonia (NH3) and water (H2O). Thus, carbon, nitrogen and oxygen were available as their saturated compounds.
As the earth atmosphere became cool, its water got collected in pits on earth′s surface. Thus reservoirs oceans were formed. It was quite nature that rocks was evaded in the process.
Thus chlorides and phosphates were added to water. Thus a condition was created for formation of various chemical compounds. |
Organic compounds: |
- As the time passes, various sugar, amino acids, nitrogenous bases and similar chemicals were formed from water and other chemicals in the atmosphere.
- Still later polysaccharides, polypeptides and nucleotides developed.
- The source of energy for this were ultra violate radiations, sparks of lightening and dry heat released during volcanic eruptions.
- Because of the lack of oxygen, these organic compounds can′t be degraded.
- Thus, their concentration increased. This phase can be considered as chemical evolution.
- Such transformations are not possible in today′ oxidizing atmosphere.
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Miller′s Experiment: |
- The scientist Miller has created artificially in the laboratory, a primitive, probable atmosphere and demonstrates the possible transformations described earlier.
- He took a mixture of water (H2O), methane, ammonia and hydrogen gases in airtight container called ‘reaction chamber’.
- To generate electric spark electrodes were arranged.
- The chamber was connected with another vessel in which water can be boiled to generate steam.
- At the other end of reaction chamber, a condenser was located to cool the vaporous mixture and collect it.
- This mixture can be tested for the presence of various chemical.
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- After a period of about eighteen days, the collected mixture showed the presence of organic compounds like amino acids and peptide chains.
- Thus we can say that such events were possible in primitive atmosphere of earth.
- Later other scientists carried out similar experiment using ultraviolet radiation and obtained similar results.
- Adenine and other nitrogenous bases were also formed in a similar way.
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Formation of Macromolecules: |
Amino acids, nitrogenous bases etc. might be formed earlier but its concentrations is very low.
For acromolecules like polysaccharides, polypeptides are to be formed, some special conditions
need to required.
There will be a requirement for the sufficient concentration of monomers, the chances of bond
formation amongst them and survival of polymers against degradation. By the process of
evaporation, condensation and accumulation on soil particles, the concentration of organic
compound may increased.For origin of life the conditions still to be created. For that, first
requirement was of formation of macromolecules which can self replicate. It was also
essential be maintained. Such compounds had to be partially isolated from outside environment.
Two such structures may have been formed.
(1)Coacervates
(2)Micro spheres
(1)Coacervates :
(a) When polysaccharide and large size of proteins are properly mixed.
Coacervates are formed.This was demonstrated by Oparin (1923).
(b) It is also known as pre – cells or pre – bionts.
(c) In it, there is an outer aqueous envelope within which proteins and polysaccharides
remain closed.
(d) They do not posses liquid membranes around them.
(e) They cannot self – replicate. Thus, they cannot be considered living. |
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(2)Microspheres:
(a) Coacervates developed the ability to grow and divided giving rise to microsphere that were separated
from their environment by lipid membrane.
(b) They could grow by absorbing materials from outside and they could also increase in number by
budding. |
Sydney Fox′s Experiment :
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- Proteinaceous microsphere: Sydney Fox heated a mixture of dry amino acids at a high temperature and then cooled it with cold water. He obtained proteinaceous microsphere.
- Their size was nearly the round shaped bacteria.
- Moreover, they can be constrict from the middle and separate into two units.
- However, it is not clear as to how these structures became isolated from their environment.
- When organic compounds like proteins, nucleic acids and other complex molecules and a source of energy became available, life may be originated.
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Biological Evolution :
The first cells were formed from organic material and there was no oxygen in their atmosphere. As a source of energy, they must have depended on fermentation of organic matter. The same matter, they have web for nutrition. Thus, nutrition must have been heterotrophic.
With the passage of time, first chemosynthetic and later photosynthesis forms of cells, must have come into existence.The release of molecular oxygen (O2) in the atmosphere is occur by photosynthetic activities. There is an important event in history of earth.
The reducing atmosphere got gradually converted into an oxidizing one. At the same time ozone layer was created as ozone got generated. Due to the availability of O2, aerobic method of respiration got developed. Today′s environment is oxidizing type. Thus organic compounds can not be formed by themselves.
Oparin and other scientists believe that life has originated only once on earth. All other forms of life have evolved from it in cause of time. |
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- Editorial Team, |
MINDFIESTA |
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Evolution of Life
