Origin of Universe and Earth.                                                                                                                            

Philosophers and scientists have been busy to solve the riddle as to how the universe and our earth were formed and how and when 'life' originated on earth. The branch of life science for the study of 'Origin of life' and evolution of different forms of life on earth was called Bioevolution or Evolutionary Biology by Mayer, (1970).

The study of universe or cosmos is called Cosmology. Our earth belongs to the Solar system having nine stars called planets constantly rotating around a common Sun. On the basis of the order of the distance from the sun these planets include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto while moon is a satellite of earth. The universe is made up of matter and energy and it was formed about 10 to 13 billion years ago as a red hot, dense, rotating gaseous cloud of cosmic dust called Ylem or primaeval matter. The Ylem consisted of particles of matter (like neutron, proton and electron) and antiparticles of antimatter. Scientists like Lemaitre (1931), Gamow (1948), Dicke (1964) etc. supported the Big-Bang Hypothesis which explains that collision between these particles and antiparticles caused a tremendous explosion to form atoms of hydrogen. Cosmic evolution began with the fusion of hydrogen atoms with progressively heavy atoms of different elements. Stellar systems and stars were formed by spreading of original gaseous cloud into the space and divided into smaller and larger masses. Most of the stars are masses of red hot gases even today.

Kant (1755) and Laplace (1796) supported Nebular Hypothesis which explains our solar system to have evolved about 4.5 to 5 billion years ago from a rotating red-hot gaseous cloud containing millions of free atoms of different varieties. First of all sun was formed when this cloud condensed, next the planets were thrown off from the sun and later on, in turn satellites were thrown off by planets. However, Nebular hypothesis was rejected by astronomers of present century like Weizsacker (1944), Alfen (1950) and Hoyle (1955).

According to them the sun was originally surrounded by a disk of rotating gas. Later many rotating concentric whorls were formed by break up of the disc and by gravitation and rotation particles of each whorl collected and condensed to form a planet. Our earth was formed about 4.6 billion years ago as a red hot gaseous cloud of free atoms with temperature of 5000^o to 6000^oC.

Structure of present earth. The earth is orange like in shape. Its pole to pole diameter is 12640 km and equatorial diameter is 12783 km. It is about 15

crore km away from sun and about 484000 km away from moon. Due to tremendous temperature gases existed in atomic form but gradually they cooled down in hundreds and millions of years into molten core. According to density other elements got stratified. Earth contains the central solid core, the middle mantle and shell and outer crust. The earth rotates at its polar axis in one day and it rotates

around the sun in 365 1

2

days or one year.

 Origin of Life.                                                                                                                                                         

Life is the part and parcel of the universe and both are very intimately associated with each other. We know that “Life is the most unique, complex organisation of molecules, expressing itself through chemical reactions which lead to growth, development, responsiveness, adaptation and reproduction” that matter has achieved in our universe. Origin of life is a unique event in the history of universe.

 

 

1. Ancient theories of origin of life : Various theories have been put forward to explain the phenomenon of origin of life. A few of them were only speculations while others were based on scientific grounds. These theories are –

1. Theory of special creation.
2. Theory of spontaneous generation or Abiogenesis.
3. Biogenesis
4. Cosmozoic theory.
5. Theory of sudden creation from inorganic material.
6. Naturalistic theory.

1. Theory of special creation : According to a Spanish Priest Father Suarez (1548 – 1617 B.C.), the whole universe was created in six days by the God. First day Earth and heaven, second day sky, third day dry land and vegetation, fourth day Sun, Moon and other planets, fifth day fishes and birds, and sixth day human beings other animals were created by God. This theory was based on some supernatural power.
2. Theory of spontaneous generation or Abiogenesis : This theory postulates that life originated from non-living matter spontaneously from time to time. This theory was supported by Plato, Aristotle, Anaximander, John Ray, Needham, Von Helmont, etc., upto the end of seventeen century. Huxley (1870) criticised this theory and propounded the theory “life originated from preexisting life only.”

• Abiogenesis means origin of life from non-living organisms.

3.  

Ridi’s Experiments

Biogenesis : Scientists like Redi (1668) Spallanzani (1767), Louis Pasteur (1866–1862) provided experimental support for the Biogenesis concept of Huxley.

 

Francesco Redi (1668) showed that maggots could not be created from meat. Actually, the smell of meat attracts flies which lay eggs on the flesh. These eggs hatched into flies.

Spallanzani (1767) showed that even primitive, unicellular organisms cannot arise from non-living matter.

 

Pasteur’s experiment with swan-necked flasks

Louis Pasteur (1860-62) obtained air samples in the flasks of broth (yeast and sugar solution) whose drawn-out necks were sealed cooling these contained a partial vaccum. Where a sample was required, the flask was opened. Air was drawn in and the flask was resealed. Flasks were incubated. These flasks which were opened in the streets became turbid while those exposed to dust-free air rarely contained bacteria.

 

 

Louis Pasteur also, used swan-necked flasks whose long, curved necks permitted exchange of air between outside and inside of the flask, but dust and bacteria were trapped along the wall of the neck. On tilting the flask, the bacteria got washed down into the broth, so that the latter became cloudy due to bacterial growth.

4. Cosmozoic Theory : Richeter (1865), Preyer (1880), Arrhenius (1908), Hoyle (1950) and Bondi (1952) believed in eternity of life. According to Arrhenius life was transferred from “cosmozoa” (life of outer space) to different

 

 

 

planets small units called ‘spores’. The spores were covered by a thick protective covering. When the spores got favourable conditions and temperature, the spore coat was dissolved and gave birth to initial living organisms. This theory does not explain as to how the life originated in space and how the life originated in spores remain impenetrable by ultraviolet and gama rays.

5. Theory of sudden creation from inorganic material : Cuvier (1769-1832) believed in catastrophism. According to him, the catastrophy destroys the whole life on earth, and after that, new life originates called it as Mechanistic theory.
6. Naturalistic Theory : Haldane, a British scientist, stated that in the early atmosphere of gas mixture probably carbon dioxide, ammonia and water vapours were predominantly present. When ultraviolet rays reacted on them, organic molecules were formed. Gradually, quantity of these oceans which later gave rise to amino acids, proteins, carbohydrates, nucleic acids, etc.

2. Oparin's Modern Theory : Oparin (1924) proposed that “life could have originated from non-living organic molecules.” He believed in Biochemical origin of life. Haldane (1929) also stated similar views. Oparin greatly expended his ideas and presented them as a book “The origin of life” in 1936.

According to this theory, the Earth originated about 4,500 million years ago. When the earth was cooling down, it had a reduced atmosphere. In this primitive atmosphere nitrogen, hydrogen, ammonia, methane, carbon mono-oxide and water were present. Energy was available in the form of electric discharges by lightening and ultraviolet rays. As soon as the earth crust was formed, it was very much folded. Torrential rains poured over the earth for centuries and were deposited in deep places.

The atmospheric compounds, inorganic salts and minerals also came in deep places oceans, these molecules gave rise to a variety of compounds and finally to the self-duplicating molecules. Ultimately these molecules were enclosed in membranes derived from lipids and proteins, along with water and chemical compounds, giving rise to cell like units. Again random combinations may have led to the formation of chlorophyll– containing organisms which could produce their own food (autotrophs) by a process called photosynthesis. These organisms had a better chance to live because

they synthesise starch from carbon dioxide and water in presence of

sunlight. Starch could be used as further source of energy. During photosynthesis, oxygen was produced. The oxygen was used by

According to Oparin’s hypothesis–Origin of cells from coacervates

other organisms for respiration. Also oxygen, when acted upon by ultraviolet rays, formed ozone layer through which ultraviolet rays cannot pass. This layer is formed about 25 km. from earth's surface. After the formation of ozone layer, organisms could come to the surface of the ocean and could survive even on land, if thrown out of oceans. The Oparins's and Haldane's theory of origin of life is most accepted these days as it is supported by Miller's experiment duly supported by David Buhal, Melvin Kelvin's experiment etc.

• O₂ is absent in the primordial atmospheres at the time of origin of life.

Miller's Experiment : An American scientist (Biologist) Stanley Miller (1953) performed an experiment under support Oparin's theory of origin of life. He believed that basic compounds which are essential for life can be

 

 

synthesised in the laboratory by creation in the laboratory, on a small scale, the conditions which must have existed at the time of origin of life on earth.

Miller took a flask and filled it with methane, ammonia and hydrogen in proportion of 2:1:2 respectively at 0°C. This proportion of gases probably existed in the environment at time of origin of life. This flask was connected with a smaller flask, that was filled with water, with the help of glass tubes. In the bigger flask, two electrodes of tungsten were fitted. Then a current of 60,000 volts was passes, through gases containing bigger flask for seven days. At the end of seven days, when the vapours condensed, a red substance was found in the U-tube. When this red substance was analyzed, it was found to contain amino acids, Glycine and nitrogenous bases which are found in the nucleus of a cell.

 

 

• An experiment to prove that organic compounds were the basis of life, was performed by miller.

From the above theory we conclude that life first originated in water. Therefore, water still continues to be an essential constituent of life.

The entire process of the origin of life, as proposed by Oparin, can be summarised as under –

(a)The Chemical Evolution :

1. Step 1 : Formation of simple molecules : The reactions between simple atoms like carbon, hydrogen oxygen and nitrogen in the primitive atmosphere led to the formation of simple compounds like water, ammonia and methane. But since the earth was very hot, all these substances remained in the form of vapours in the atmosphere. Gradually, as the earth started cooling down, the dense clouds began raining on the earth. But the liquid was still very hot. Therefore, as the liquid water touched the earth's surface, it again got vaporized to be returned to the atmosphere. This process continued for millions of years. As a result of these heavy downpours, the earth's surface got filled with water to form rivers and oceans. Ammonia and methane got dissolved in the oceanic water. The mineral elements, which were dissolved in rivers, were also carried into the oceans when rivers joined it.

The scientists have found that simple unicellular organisms (resembling modern cyanobacteria) were present on this earth about 3600 million years ago. It is believed, therefore, that life must have originated on this earth about 4600 to 3600 million years ago.

It must be clear that the earth's atmosphere at that time was quite different from as it exists today. The earth's atmosphere at that time was reducing, not oxidizing (as it is today). The primitive atmosphere of earth had hydrogen, nitrogen, water vapours, carbon dioxide, methane and ammonia abundance. Oxygen was not available in free state in sufficient quantities.

 

 

2. Step 2 : Formation of Simple organic compounds : Continuous rains provided opportunities for different types of molecules to collide with each other and react. Methane is an active compound, and it reacted with other compounds to form organic compounds like ethane, butane, propane, ethyl alcohol. From such organic compounds which were formed in the ocean and which played a role in the origin of life include –
   1. Sugars, glycerol and fatty acids : These were formed by the combination of carbon, hydrogen and oxygen.
   2. Amino acids : These were formed by the combination of carbon, hydrogen, oxygen and nitrogen.
   3. Pyrimidines and Purines : These were formed by the combination of carbon, hydrogen and nitrogen.

These compounds were formed at the time when sunlight could not reach earth because of dense clouds in the sky. Under such circumstances, the energy required for the synthesis of above–mentioned chemical substances must have been obtained from the cosmic rays and lightening in the sky. Even today, NH₃ and other compounds are formed in the atmosphere during electric discharges. Thus, it is clear that all the amino acids required by living organisms could be formed in the condition of primitive atmosphere. However, this type of synthesis requires reducing atmosphere because the substances produced through these processes get destroyed by oxidation on coming in contact with oxygen. Since free oxygen is available in the atmosphere today, present day atmosphere is no longer reducing–it has turned oxidizing. Therefore, in the present circumstances, such a synthesis of chemical substances is not possible.

3. Step 3 : Formation of complex organic compounds : The simple organic compounds combined in different ratios to form complex organic compounds like polysaccharides, fats and proteins.
   1. Simple sugars combined in different ratios to form polysaccharides like starch, cellulose, glycogen etc. The formation of such compounds had been very important for the origin of life because cell walls are made up of cellulose and energy–giving molecules are stored in the form of starch and glycogen.
   2. The reaction between glycerin and fatty acids yielded fats.
   3. Different types of combinations between a variety of amino acids yielded different types of proteins. The formation of protein was a very important step in the origin of life because proteins are not only structural components of cell organelles, but many proteins, called enzymes, work as catalysts for biochemical reactions.

In fact, the present day organisms synthesise their complex molecules from simple organic substances with the help of enzymes only. However, enzymes themselves are proteins. Therefore, first of all protein must have been synthesized without the help of any enzyme.

4. Step 4 : Formation of nucleic acids and nucleoproteins : You have already learnt that the reaction between methane, ammonia and water resulted in the formation of purines and pyrimidines. Some of the purines and pyrimidines combined with sugar and phosphorus to form nucleotides. Many molecules of nucleotides combined to form nucleic acids–DNA and RNA. The formation of nucleic acid in the oceanic water was a big steps in the direction of origin of life. Nucleic acids combined with the proteins to form nucleoproteins. Some of the nucleoproteins developed the capability to synthesise molecules similar to themselves, from organic and inorganic substance present in the ocean. In other words, the capability to reproduce had evolved. As a result of continuos reproduction, the number of nucleoproteins went on increasing. Since, organic substance were required for this, the organic substances started being depleted resulting in competition between the nucleoproteins. Physical and chemical changes sometimes led to the changes in the competition of nucleoproteins, and new types of nucleoproteins came into existence by mutations. Those new nucleoproteins which were successful in the competition, increased in number.

 

 

 

 

 

 

 

 

 

Ni

Lava   Fe

 

 

Other Metals

 

 

 

 

 

 

 

 

Amino Acids   e. g., Alanine; Leucine; Glycine

Energy of ultraviolet rays

 

and electric discharge

(b)Organic Evolution :

1. Step 5 : Formation of Coacervates

Oparin believed that the formation of protein was a very important step in towards the origin of life. Due to their Zwitterionic nature, the protein molecules. This enabled these colloidal structures to maintain their identify inspite of being surrounded by water molecules–forming a type of emulsion. The coalescence of these colloidal structures led to the formation of structures called coacervates. These coacervates had the ability to exchange substances with the surrounding water and accumulating required substances within them.

• Under certain conditions scientists have obtained cell like structures. These are known as coacervates.

Sydney F. Fox's experiment : Sydney F. Fox of Florida University, obtained some complex molecules by heating upto 90°C a dry mixture of many amino acids found in living organisms. The molecules so obtained very much resembled the proteins. He heated these molecules in water and allowed the mixture to cool down. In the fluid so obtained, he could observe minute structures resembling the cells. He called them microspheres. The microspheres are surrounded by membranes, and these also reproduce vegetatively just like years. Surprisingly the biochemical processes like breakdown of glucose also occur their. However, electron microscopic examination of these does not reveal any cellular structure. On keeping in distilled water, these become turgid, but these get shrunk if immersed in salt solution. Oparin's coacervates and Fox's microspheres are infact, similar structures.

2. Step 6 : Formation of Primitive cell : A primitive cell membrane was formed by the arrangement of lipid molecules between the surface of coacervates and external watery medium. This provided stability to the coacerrates. It is believed that a primitive cell was formed when–
   1. Nucleic acids having the property of self-duplication entered the coacervates.
   2. Rearrangement of molecules occurred inside the coacervate surrounded by lipid molecules.

Earliest organisms : Evidences available so far indicate that the cells of the earliest organisms did not contain either nucleus or cell organelles. The molecules of nucleic acid were surrounded by a colloidal mixture (may be called protoplasm) of proteins and organic compounds. This, in turn, was surrounded by a thin membrane.

 

 

 

Water and soluble substances would pass through this membrane. Such cells which lacked nuclei were called prokaryotic cells. In 1966, some fossils have been discovered from 300 million years old rocks. These fossils are of prokaryotic organisms. Earliest organism is chemoheterotrops.

3. Step 7 : Origin of autotrophism : In the primitive organisms, the process of metabolism began because all the substances required for reduction were available in water. Of course, oxygen was not available which was required for oxidation of substances to yield energy. Therefore, the primitive cells respired anaerobically i.e., these used to obtain energy by fermenting the organic compounds obtained form the water, with the help of enzymes due to fast nutrition, growth and multiplication, their number in the ocean increased greatly. As a result, scarcity of organic substances developed in the ocean. A struggle started between the cells for obtaining nutrition.

At such a time, some of these organisms developed the capability of synthesizing organic substances. Such organisms began synthesizing energy– giving substances (carbohydrates) from simple inorganic substances abundantly available in the environment. In this way, evolution of autotrophs from heterotrophs took place.

This was the beginning of autotrophic nutrition. However, it was quite different from the photosynthesis which is carried out by green plants, because it utilized energy obtained by anaerobic respiration (not solar energy). Therefore, such type of nutrition is also called chemoautotrophic nutrition. Such type of nutrition is observed even

today in the sulphur bacteria.

6 CO2 + 12 H2S ¾¾Ferm¾ent¾at¾ion® C6 H12O 11 + 6 H2 O + 12 S

Chemical energy

At the same time, from different chemicals present in the oceanic water evolved porphyrins which where like modern chlorophyll led to the evolution of present chlorophyll, so that these cells started utilizing H₂ O instead of

H₂S for photosynthesis.

6 CO2 + 12 H2S ¾¾^Sol¾^ar ®  C6 H12O6 + 6 H2 O + 12 S

Energy

Till then, oxygen was not freely available in the atmosphere. However, gradually molecular changes in the bacteriocholorophyll led to the evolution of present chlorophyll, so that these cells started utilizing H₂O instead of

H₂S for photosynthesis.

6 CO2  + 12 H 2 O ¾¾^Sol¾^ar ® C6 H12 O6  + 6 H 2 O + 6O2

Energy

In this way, the prokaryotic cells which were chemoautotrophs, became photo autotrophic. These cells resembled modern cyanobacteria. In 1968, the forms of such types of cells have been recovered from 320 million years old rocks. These have been given the name Archaeospheroides barbertonensis. Due to the absence of well- defined nuclei in them, these have been included under the kingdom ‘Monera’. Thus, release of O₂ in the atmosphere and its free avilability was the result of photosynthesis. This was a revolutionary change which greatly affected the course of organic evolution.

4. Step 8 : Origin of Eukaryotic cells : As a result of photosynthesis, oxygen was released in the atmosphere which started reacting with methane and ammonia in the atmosphere. Its reaction with methane yielded CO₂ and H₂O. On the other hand, reaction between oxygen and ammonia resulted in the formation of CO₂ and nitrogen. In the course of these changes, Ozone (O₃) gas was formed from oxygen; the ozone spread in the form of an envelope surrounding the earth, the distance between the ozone layer and the earth's surface being approximately 15 miles. As free oxygen became available on the earth, gradual changes took place in cell structure also. Membrane – bound organelles i.e., mitochondria, chloroplasts, golgi bodies, lysosomes evolved. Thus, prokaryotic cells. Most of the organisms on the earth today are eukaryotic.Gradual changes in the earth's atmosphere led to gradual changes in the eukaryotic cells also. Instead of living separately, the cells started living together in the form of colonies. Simultaneously, multinucleation of multicellular structures forming tissues. Different

 

 

types of tissue combined to form special organs. From the organs, organ systems and ultimately complex bodies of organisms were formed.

• Organic evolution would have not been taken place if individuals in a population did not show genetic variation.
• Synthetic theory is the most accepted theory of organic evolution.
• The greatest evolutionary change enabling the land vertebrates to be completely free from water, was the development of shelled eggs and internal fertilization.
• The material for organic evolution is mutation.

 Evidences of Organic Evolution.                                                                                                                      

The following are the evidences in favour of Organic Evolution :

(i) Evidences from Classification                       (ii) Evidences from Comparative Anatomy

1. Analogy and Homology
2. Vestigeal organs

(iii) Evidences from Physiology                        (iv) Evidences from Serology

(v) Evidences from Embryology                  (vi) Evidences from Palaeontology

(vii) Evidences from geographic distribution          (viii) Evidences from Genetics

1. Evidences from Classification : All the known living animals and plants have been classified into various species, genera, families, order, classes, phyla and kingdoms. The classification of a particular animal is attempted only after its extensive study. It is seen that every living being is related with other living being. The relations may be very close or may be quite apart. On their relationship, they are put under various orders, classes, phyla etc. On the superficial examination one can hardly believe that they are interrelated. But after their careful study they can be arranged in definite order, Protozoa (acellular) being at the base while Chordata at the top. No doubt, there is some sort of gap between chordates and non-chordates today but who known that this gap may be filled some day by some further discoveries. Moreover, the present-day types represent only the terminal twigs of a vast phylogenetic tree and for establishing relationship we should focus our attention on the main trunk. The animals can be classified as described above in a systematic order.
2. Evidences from Comparative Anatomy : In all the living animals, the basic substance of life is Protoplasm. If the species had been created separately, then there should be no relationship in the various organs and systems of animals. But on the contrary, we see that large number of animals although unlike in appearance show most of the systems and organs made on the same plan. The resemblance are very close in the members of the same group. For example –

1. Analogy and Homology : While examining the various structures in the bodies of different animals, one may come across certain organs of same origin but of different functions. For example, the forelimbs of salamander, crocodile, bird, bat, whale, and man, all have the same origin and essential structures but different functions to perform. Such structures are called homologous. On the other hand, the wings of insect, pterodactyle, bird and bat perform the same function, though they have different origin and entirely different structures. Such structures are termed analogous.

The homologous structures give us the answer that how the two different types of animals or organs have the same origin and functions to perform; this shows that they have changed themselves according to their different needs.

• Analogous organs are those, which are functionally similar.

 

 

 

• Homologous organs explains divergent evolution.
• Similarity developed in distantly related groups as an adaptation to the same function is called convergent evolution.
• The wings of an insect and a bat exhibit analogy.

 

 

 

 

 

 

 

 

 

 

1. Homology in the forelimbs of vertebrates

 

2. Vestigeal organs : There are present in the body of animals certain structures which have no function and are very much reduced. These structures are quite developed and

functional in allied animals. Such useless organs are termed as vestigeal and are of frequent occurrence. In human body alone, there are as many as ninety such organs. For example, vermiform appendix is vestigeal in man but functional in rodents, horse and other herbivorous animals.

• Vermiform appendix is the Vestigeal organ in man.
• Hind limbs is a vestigeal organ of python.
• Muscles of ear pinna is vestigial organ of man.
• Wisdom teeth is vestigeal organ of man.

3. Evidences from Physiology : Various types of chemical tests exhibit many basic similarities in physiological and chemical properties that show a physiological relationship among animals.

Take the example of thyroxin hormones, which are similar in all

metabolism. The thyroid of human beings can be very easily replaced by the thyroid of cattle without any ill-effects and so on.

Different vestigial organs in man

4. Evidences from Serology : This is a method by which the reactions of blood serum is observed. From the blood are also extracted the crystals of Oxyhaemoglobin. The structure differs in different vertebrates, but in a definite order. The reaction is nearly identical in man and anthropoid monkeys, but slightly less identical with other mammals.
5. Evidences from Embryology : With the exception of a few, every multi-cellular animal originates from a zygote. The development from zygote to adult shows many similarities in various organisms. The development is termed as ontogeny.

Haeckel, a German biologist, gave a theory “Ontogeny repeats Phylogeny”. An individual organism during its development (ontogeny) tries to repeat the history of its race by different stages (phylogeny). The vertebrate development confirms the above statement. For example, the embryos of all vertebrates pass through a gilled stage. In fishes, the gills are present in the adult condition. In amphibians, gills are present in some forms of frog and in

 

 

tadpole. While in reptiles, birds and mammals these gills are never functional but nevertheless they are always present in the embryo.

Haeckel, believed that all those stages, which have occurred during the course of evolution of a particular animal, also pass through its development.

There are objections to this theory, but is throws enough light to show the interrelationship of animals.

6. Evidences from Palaeontology : The study of fossils and their interpretation forms one of the great evidences of evolution. An Italian scientist, Leonardo da Vinci, was the first person to recognize their importance and said they were either remains of organisms of their impressions on some sort of clay or rock.

A number of fossils have been discovered from time to time. Some of these fossils are very prefect in their state of preservation. For example, the fossils Archaeopteryx shows the characters of reptile on the one hand, and the characters of birds on the other hand, meaning that the birds have evolved from reptiles, the Archaeopteryx being a connecting link.

In the same way all the evolutionary stages of horse, elephant, camel and man etc., can be constructed. The earliest horse was known as Eohippus. It was eleven inches in height and made its appearance in Eocene time from some unknown five-toed ancestor. The Eohippus, after various evolutionary stages, transformed itself into the present-day horse Equus, which shown many dissimilarities from its great grand, grand ancestor. The various stages in its evolutionary life had been preserved as fossils. The same is the case with camel, elephant and man, etc. So this science of paleontology helps in a great deal in understanding the process of evolution.

• Wallace gave a theory very similar to that of Darwin.
• In Cenozoic era mammals and birds were evolved.
• There was no life in Azoic era.
• Fossils are remains of organisms present in the rocks.
• Ruling reptiles were dominant during Mesozoic era.

 

Era	Age million years	Period	Epoch	Dominated Fauna
Cenozoic (Age of Modern life)	0.1	Quaternary	Recent (Holocene)	Modern man, mammals, birds, fishes, insects.
	2.5		Pleistocene	Extinction of grate mammals. Primitive man common. Evolution of human society & culture.
	7	Tertiary	Pliocene	Evolution of primitive man–like forms from man like apes. Formation of modern mammals.
	2.5		Miocene	Mammals at peak. Evolution of man–like apes.
	3.8		Oligocene	Decline of egg laying and marsupial mammals. Rise of first monkeys and apes.
	5.4		Eocene	Diversification of placental mammals.
	6.5		Paleocene	Rise of first primates, placental mammals and modern birds.

 

Mes ozoi c (Era

135

Cretaceous

Extinction of dinosaurs and toothed birds. Rise of first modern birds.

 

 

	195	Jurassic (Age of Giant Reptiles)	Origin of advanced lizards, crocodiles, alligators, marsupials toothed birds. Dinosaurs became large. Reptiles dominant.
	240	Triassic	Origin of dinosaurs & primitive mammals (egg–laying mammals). Extinction of primitive amphibians.
Paleozoic (Era of Ancient life)	285	Permian	Extinction of many marine invertebrates like trilobites. Rise of modern insects. Evolution of mammals like reptiles.
	375	Carboniferous (Age of Amphibians)	Origin of reptiles and winged insects.
	420	Devonian (Age of fishes)	Origin of first land vertebrates (amphibians) Fishes abundant.
	450	Silurian	Origin of jawed fishes and wingless insects.
	520	Ordovician (Age of invertebrates)	Origin of chordates with first jaw– less fishes (origin of vertebrates). Invertebrates abundant.
	570	Cambrian	All invertebrate phyla established. Trilobites (swimming crustaceans which do not exist today) dominant
Proterozoic (Era of early life)	2300   3600   3800   4600	Pre–cambrian	Origin of marine metazoans including sponges, cnidarians, annelids, molluscs and arthropods. Scanty fossils. Origin of prokaryotes (Monera) and Eukaryotes (Protista). Origin of life.
Archeaozoic (Era of invisible life)			No life?

(a)Fossils :

1. Direct evidences of organic evolution are provided by fossils (L. fossil, dug up).
2. The science of discovering and studying fossil record is called Palaeontology (Gr. palaeo, ancient; logy, study of).
3. Fossils are remnants, models and impressions of extinct organisms.
4. Fossils are found preserved in earth's sedimentary rocks.
5. Fossil may be an entire organism buried in sediment or snow, small part of ancient organism or impression of ancient leaf or stem.
6. Fossilization occurs where organisms are buried and preserved by natural processes.
7. Petrifaction is the most usual type of fossil in which hard parts like bones, shells, teeth or trunk of trees are preserved.

 

 

8. Other types of fossils are moulds, casts and compressions. A compression is a common type of plant fossil formation.
9. A compression is formed when the internal structure of plant is lost leaving a thin carbon film which gives the outline of the original plant.
10. When the contents of intestine of ancient animals are preserved, it is known as coprolite.
11. Palynofossils are tiny microscopic spores, pollen and other vegetal remains of the past.
12. Pseudofossils are formed by minerals which crystalize and develop into patterns resembling outlines of plants.
13. Twenty million years old fossil forests have been discovered and studied by the Birbal Sahni Institute of Palaeobotany, lucknow.
14. About 25,000 years old frozen elephant-like mammoths were found buried in ice in Siberia in the early part of this century.
15. Leonardo da Vinci (1452-1519) is called the father of Palaeontology.
16. The modern palaeontology was established by Georges Cuvier (1769-1832) and referred to as 'Founder of modern Palaeontology'.
17. Palaeontological study helps in understanding and locating coal and hydrocarbon sources.

(b)Age of fossils :

1. The age of the fossils or rocks can be determined by ‘Clock of the rock method' or 'Radioactive clock’.
2. 'Clock of the rock' method is based on conversion of unstable radioactive nuclei into stable nuclei over a fixed period.
3. Radioactive clock method was introduced by Boltwood in 1907.
4.  

The common radioactive elements which lose their radioactivity and change into their non-radioactive isotopes at a fixed rate are :

 

Important living fossils

 

1. Peripatus (Arthropoda)	2. Limulus (Arthropoda)
2. Nautilus (Mollusca)	4. Neopilina (Mollusca)
5. Lingula (Brachiopoda)	6. Latimeria (Coelacanth fish)
7. Sphenodon (Reptilia)