ENS 411 Unit 1 PDF

Lecture Outline-Dr. M T Das ENS-411 Fundamentals of Ecology & Environmental Science Unit I– Origin of Earth and Evolution of Life Concepts on origin of our Universe (big bang theory) and our solar system (Nebular condensation theor...

Lecture Outline-Dr. M T Das ENS-411 Fundamentals of Ecology & Environmental Science Unit I– Origin of Earth and Evolution of Life Concepts on origin of our Universe (big bang theory) and our solar system (Nebular condensation theory); Evolution of early earth and it’s atmosphere; Origin of earliest life forms Origin of earliest life forms (Millers experiment, RNA Life, Origin of early prokaryotes, Stromatolites, Origin of early eukaryotes); Theories of biological evolution (basic outlines of Lamarkism, Darwin’s theory, Mutation theory and Hardy-Weinberg principle), Geological time scale, Mass extinctions, Brief account on evolution of Human. 1. Concepts on origin of our Universe (big bang theory) All of the mass and energy of the universe is thought to have been concentrated at a geometric point at the beginning of space and time. The event which lead to the expansion of the universe is named as “the big bang”, that occurred about 13.7 billion years ago. The cause of this expansion is not known till today, but the expansion of the universe continues today and will probably continue for billions of years, perhaps forever. The early universe was hot, but as it expanded, it cooled. About a million years after the big bang, temperatures fell enough and the atoms (mostly hydrogen) were formed from the energy and particles of the expanding universe. Hydrogen is the most abundant form of matter not only in the primitive universe but also in the present day universe. About a billion years after the big bang, this matter began to coagulate into the first galaxies and stars. A galaxy is a huge, rotating aggregation of stars, dust, gas, and other debris held together by gravity. Galaxies are spiral, elliptical or irregular in shape. In spiral galaxies, the stars are arrayed in curved arms radiating from the galactic center. There are perhaps 100 billion galaxies in the universe and 100 billion stars in each galaxy. Our galaxy is a spiral one named as Milky Way galaxy (from the Greek galaktos, which means “milk”). The sun and its family of planets, called the solar system, are located about three-fourths of the way out from the galaxy’s center, in a spiral arm. The solar system orbit the galaxy’s brilliant core, taking about 230 million years to make one orbit. 2. Concepts on origin of our solar system (Nebular condensation theory); The nebular condensation theory, explains how stars and planets are believed to form. Nebulae are large, diffuse clouds of dust and gas within galaxies. As per the nebular condensation theory our solar system was formed from the condensation nebular clouds formed after the death of a pre-existing large star. Birth and death of a star is a cyclic phenomenon which is described below. Birth of a star: The life of a star begins when a spinning nebula begins to shrink and heat up under the influence of its own weak gravity. Gradually, the cloud like sphere condenses at the center to form a protostar. The original diameter of the protostar may be many times the diameter of our solar system, but gravitational energy causes it to contract, and the compression raises its internal temperature. When the protostar reaches a temperature of 1 about 106 °C, nuclear fusion begins. That is, hydrogen atoms begin to fuse to form helium, a process that liberates even more energy. This rapid release of energy, which marks the transition from protostar to star, stops the young star’s shrinkage. Death of a small or medium star: After fusion reactions begin, the star becomes stable—neither shrinking nor expanding, and burning its hydrogen fuel at a steady rate. Over a long period, the star converts a large percentage of its hydrogen to different fusion products including helium, carbon or oxygen which are further used as fusion fuels. When a medium-mass star (like our sun) begins to consume carbon and oxygen atoms, its energy output slowly rises and its body swells to a stage named as red giant. The dying red giant slowly pulsates, incinerating its planets and throwing off concentric shells of light gas enriched with these heavy elements. But most of the carbon and oxygen is trapped in the cooling ember at the star’s heart. Death of a large star: Stars much more massive than the sun have shorter but more interesting lives. They, too, fuse hydrogen to form atoms as heavy as carbon and oxygen; but, being larger and hotter; their internal nuclear reactions consume hydrogen at a much faster rate. In addition, higher core temperatures permit the formation of atoms—up to the mass of iron. The dying phase of a massive star’s life begins when its core—depleted of hydrogen—collapses in on itself. This rapid compression causes the star’s internal temperature to rise. When the material can no longer be compressed, a catastrophic expansion occurs called a supernova. The explosive release of energy in a supernova is so sudden that the star is blown to bits and its shattered mass accelerates outward at nearly the speed of light. The explosion lasts only about 30 seconds, but in that short time the nuclear forces holding apart individual atomic nuclei are overcome and atoms heavier than iron are formed. Gold, mercury, uranium etc. were all created during such a supernova explosion. Birth of our Solar System: As our earth contains different elements including gold, mercury, uranium etc. it is thought that the solar system was formed as result of a supernova explosion. Initially, the thin cloud or nebula, formed after a supernova explosion condensed to form the solar nebula. Then the solar nebula was affected by a shock wave which caused the condensing mass to spin. Later on, the spinning nebula absorbed some of the heavy atoms from the supernova remnant. This process happened about 5 billion years ago. The solar nebula was a rotating, disk-shaped mass of about 75% hydrogen, 23% helium, and 2% other material (including heavier elements, gases, dust, and ice). The nebula spun faster as it condensed. Material concentrated near its center became the protosun. Much of the outer material eventually became planets. New planets formed in the disk of dust and debris surrounding the young sun through a process known as accretion i.e. the clumping of small particles into large masses. The planets of our outer solar system i.e. Jupiter, Saturn, Uranus, and Neptune—were probably first to form. These giant planets are composed mostly of methane and ammonia ices because those gases can congeal only at cold temperatures. Near the protosun, where temperatures were higher, the first materials to solidify were substances with high boiling points, mainly metals and certain rocky minerals. The planet Mercury, closest to the sun, is mostly iron, because iron is a solid at high temperatures. Somewhat farther out, in the cooler regions, magnesium, silicon, water, and oxygen condensed. Earth’s array of water, silicon– oxygen compounds, and metals results from its middle position within that accreting cloud. The period of accretion lasted perhaps 30 million to 50 million years. The protosun became a star (sun) when its internal temperature rose high enough to fuse atoms of hydrogen into helium. These nuclear reactions generated solar wind of radiation which swept past the inner planets, clearing the area of excess particles and ending the period of rapid accretion. Thus, a massive star lived its life constructing different elements and then it underwent supernova explosion in order to seed the elements back into the nebular nursery of dust and gas from which our solar system formed. 2 3 3. Evolution of early Earth and its Atmosphere Formation of Earth’s Crust and Core: The young Earth was probably chemically homogeneous throughout. Then, Earth’s surface was heated by the impact of asteroids, comets, and other falling debris, combined with gravitational compression and heat from decaying radioactive elements, which caused Earth to partially melt. Gravity pulled most of the iron and nickel inward to form the planet’s core. At the same time, lighter minerals— silicon, magnesium, aluminum, and oxygen-bonded compounds—rose toward the surface, forming Earth’s crust. This important process, called density stratification, lasted perhaps 100 million years. Then Earth began to cool. Its first surface is thought to have formed about 4.6 billion years ago. Formation of moon: About 30 million years after the formation of earth, a planetary body somewhat larger than Mars smashed into the young Earth and broke apart. The metallic core fell into Earth’s core and joined with it, while the rocky mantle was ejected to form a ring of debris around Earth. The debris began condensing soon after and became our moon. First Atmosphere: During early earth’s formation, its atmosphere consisted of gases that are common in early solar system (i.e. hydrogen, helium, methane, ammonia, carbon dioxide and water vapour). Very soon hydrogen and helium escaped in to the space as earth’s gravity was very week to hold them. Most of the remaining gases were stripped away from our planet by solar winds from the energetic young sun. Second Atmosphere: The gases that had been trapped inside the newly formed earth, escaped to the surface to form a second atmosphere. The gases were released to the surface through volcanic vents by a process known as out-gassing. This second atmosphere consisted of mostly water vapour, carbon dioxide, sulfur dioxide and minor amount of other gases including nitrogen, with traces of ammonia and methane. Most importantly free oxygen was not present, hence it was called anoxic atmosphere. Third Atmosphere: Molecular oxygen was added to the atmosphere much later only when the oxygen producing photoautotroph (Cyanobacteria) were evolved during 2.8 billion years ago. (for more detail refer origin of life section) Origin of Oceans: As the hot vapors rose, they condensed into clouds in the cool upper atmosphere. After millions of years of condensation, heavy rains began to fall towards Earth, which boiled back into the clouds again. As the surface became cooler, water collected in basins and formed primitive oceans nearly 4.0 billion years ago. 4. Origin of earliest life forms There are several theories put forwarded to explain the origin of life as shown in the table. However, the Chemosynthetic or Naturalistic theory is the most scientific one on this date. Theories Proponents Description Theory of special creation Different religious Life and earth were created by some mythologies supernatural powers. Theory of Spontaneous generation Aristotle, Plato, Von Life originates spontaneously from lifeless or Abiogenesis Helmont matter Theory of catastrophism George Cuvier Cyclic- life on earth followed by catastrophe Cosmozoic theory or theory of Ritcher, Helmholtz, Life originated from the spores or seeds or Panspermia Arrhenius germs from outer world. Theory of Biogenesis Francesco Redi, Louis Life arises from pre existing life Pasteur Chemosynthetic or Naturalistic A L Oparin, J B S Life originated by the biochemical process theory Haldane 4 A L Oparin of Russia and J B S Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and that formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents. Lederberg proposed three stages of Chemosynthetic origin of life. i) Chemogeny (Origin of Biomolecules) ii) Biogeny (Origin of first living cells) iii) Cognogeny (diversification of life) i) Chemogeny: The conditions on early earth were – high temperature, volcanic storms, reducing atmosphere etc. In 1953, S.L. Miller, an American scientist created similar conditions in a laboratory scale. He created electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 800 °C. He observed formation of amino acids. In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats. Polymerisation of the simple molecules could have resulted in formation of polypeptides and polynucleotide. Further, Clay surfaces (Montmorillonite) and pyrites (FeS2) might have acted as catalysts for spontaneous synthesis of macromolecules. As free oxygen was absent in the atmosphere, these unprotected large molecule could exist in the primitive oceans called primordial soup. With this limited evidence, the first part of chemical evolution was more or less accepted. ii) Biogeny: The formation of coacervates or microspheres led to the beginning of biogeny. Coacervates or microspheres were nothing but lipoprotein vesicles capable of growth by absorption and reproduction by budding. They were also having some enzymatic property but lacked nucleic acids and metabolism. The most primitive cellular life started when coacervates acquired nucleic acids in form of RNA. RNA used to act as a genetic material as well as a catalyst (there are some important biochemical reactions in living systems that are catalysed by RNA catalysts). There is now enough evidence to suggest that essential life processes evolved around RNA. This phase of life in primitive earth is known as age of RNA life. But, RNA being a catalyst was reactive and hence unstable. Therefore, DNA has evolved from RNA with chemical modifications that make it more stable. DNA being double stranded and having complementary strand further resists changes by evolving a process of repair. Eventually, DNA became the genetic repository of the cell and the three part system DNA, RNA and Protein became universal among cells. This lead to the formation of early prokaryotes. As the primitive earth still lacked molecular oxygen, the energy generating mechanism in early prokaryotes was mostly anoxic. Initially a variety of anaerobic chemo-organotrophs (chemo-heterotroph) and chemo-lithotrophs (chemoautotroph) may have evolved in the early earth. Evidence of these early lives can be traced in the carbon- based residues in some of the oldest rocks (3.85-billion-year-old) on Earth, from Akilia Island near Greenland. Later, anoxigenic photoautotrophic bacteria may have evolved. The oldest fossilized evidence in form of stromatolites reveals that non-oxygen evolving filamentous photosynthetic bacteria evolved nearly 3.5 billion years ago. These stromatolites are nothing but fossilized microbial mats consisting of layers of filamentous prokaryotes and trapped sediments found from northwestern Australia. 5 A milestone in earth’s history occurred with the evolution of cyanobacteria capable of oxygenic photosynthesis. Cyanobacteria first appeared on earth around 2.8 billion years ago, but the oxygen they produced did not accumulate in the atmosphere as the oceans were then rich in reducing substances such as FeS. FeS reacted spontaneously with oxygen to form iron oxide (Fe 2O3). These iron oxides can be seen today in form of sedimentary rocks with alternate iron rich and silica rich layers. These sedimentary deposits are known as banded iron formations found throughout the globe. Once all FeS were consumed from oceans, Oxygen started accumulating in the atmosphere nearly 2.2 billion years ago. Once oxygen accumulated in the atmosphere ozone layer formed which protected the earth from UV radiation from sun. The present day oxygen concentration (21%) was reached only 1.5 billion years ago. This is the time when the earth became suitable for early eukaryotes with aerobic respiration. Primitive eukaryotes, archaea and bacteria all originated from a common ancestor and evolved independently side by side. Evidences to show how the nucleus originated in primitive eukaryotes is lacking till date. However, the cellular organelles originated in eukaryotes, by a process known as endosymbiosis which occurred only after the atmosphere became oxidizing. Mitochondria in modern eukaryote were formed after the symbiotic uptake of a bacterium by a primitive eukaryote. Similarly chloroplasts were formed after the symbiotic uptake of a cyanobacterium by a primitive eukaryote. The discovery of DNA in chloroplast and mitochondria support this theory. iii) Cognogeny (diversification of life): It is the process of diversification of the primitive life forms. This happened by the process of evolution as discussed in next section. 5. Theories of biological evolution 5.1 Lamarkism: Lamarckism is the first theory of evolution, which was proposed by Jean Baptiste de Lamarck (1744-1829), a French biologist. Although the outline of the theory was brought to notice in 1801, but his famous book “Philo sophic Zoologies” was published in 1809, in which he discussed his theory in detail. Lamarckism includes four main propositions. (i) Internal Vital Force: All the living things and their component parts are continually increased due to internal vital force. (ii) Effect of Environment and New Needs: Environment influences all types of organisms. A change in environment brings about changes in organisms. It gives rise to new needs. New needs or desires produce new structures and change habits of the organisms. Doctrine of desires is called appetency. (iii) Use and Disuse of Organs: If an organ is constantly used it would be better developed whereas disuse of organ results in its degeneration leading to formation of vestigial organs. (iv) Inheritance of Acquired Characters: Whatever characters that an individual acquires in its life time due to internal vital force, effect of environment, new needs and use and disuse of organs, they are inherited to the next generations. The process continues. After several generations, the variations are accumulated upto such extent that they give rise to new species. Example Evolution of Giraffe: The ancestors of giraffe were bearing a small neck and fore limbs and were like horses. But as they were living in places with no surface vegetation, they had to stretch their neck and fore limbs to take the leaves for food, which resulted in the slight elongation of these parts. Whatever they acquired in one generation was transmitted to the next generation with the result that a race of long necked and long fore-limbed animals was developed. 6 Criticisms: The first proposition of the theory does not have any ground because there is no vital force in organisms which increases their body parts. As regards the second proposition, the environment can affect the animal but it is doubtful that a new need forms new structures. The third proposition, the use and disuse of the organs is correct up to some extent. The fourth proposition regarding the inheritance of acquired characters is disputed. Theory of Continuity of Germplasm: August Weismann (1834-1914), a German biologist, was the main opposer of the inheritance-of acquired characters. He put forward the theory of continuity of germplasm. According to Weismann, the characters influencing the germ cells are only inherited. There is a continuity of germplasm (protoplasm of germ cells) but the somatoplasm (protoplasm of somatic cells) is not transmitted to the next generation hence it does not carry characters to next generation. Weismann cut off the tails of rats for as many as 22 generations and allowed them to breed, but tailless rats were never born. 5.2. Darwin’s theory: In 1831 Darwin got an opportunity to travel on H.M.S. Beagle (a ship) for a voyage of world exploration. The voyage lasted for five years (1831-1836) during that period Darwin explored the fauna and flora of a number of continents and islands including Galapagos Islands. Galapagos Islands consist of 14 main islands and numerous smaller islands which lie on the equator about 960 Km off the West Coast of South America in the Pacific Ocean. These islands are volcanic in origin and are called “a living laboratory of evolution. Darwin visited these islands in 1835 and spent a month there. He observed great variations among the organisms that lived on these islands, which helped him to construct his theory of evolution. In 1798 T.R. Malthus, a British economist, put forward a theory of human population growth. Darwin came across this essay after his return from the voyage during 1838 and was much influenced by Malthus Theory of human population growth. While Darwin was busy in formulating his theory of natural selection, he received a brief essay from Alfred Wallace in June 1858. Alfred Wallace (1823-1913), a naturalist from Dutch East Indies was working on Malay Archipelago (present Indonesia). The essay was titled “On the Tendencies of varieties to Depart Indefinitely from the original type”. Darwin and Wallace in respect of organic evolution were similar. Finally in November 1859 Darwin published his observations and conclusion in the form of book. The full title of his book was “on the origin of species by means of Natural Selection: The Preservation of Races in the Struggle for life”. The salient features of Darwin’s Theory of Natural Selection are given below. i. Over production (Rapid Multiplication): All organisms possess enormous fertility. The organisms that have shorter life span produce large no of offspring and organisms that have longer life span produce less no of offspring. Thus population of every organism multiplies in geometric ratio. ii. Limited Food and Space: Though there is rapid multiplication in population, food and space and other resources remain limited. iii. Struggle for Existence: Limited resource gives rise to struggle for existence. This, struggle helps in restricting the number of individuals of particular species. The struggle for existence can be of three types. (a) Intraspecific Struggle: It is the struggle between the individuals of the same species because their requirements like food, shelter, breeding places, etc. are similar. Many human wars are the examples of intraspecific struggle. Cannibalism (eating the individuals of its own species) is another example of this type of struggle. (b) Interspecific Struggle: It is the struggle between the members of different species. This struggle is normally for food and shelter. For example, a fox hunts out a rabbit, while the fox is preyed upon by a tiger. 7 (c) Environmental Struggle: It is the struggle between the organisms and the environ mental factors, such as drought, heavy rains, extreme heat or cold, earthquakes, diseases, etc. iv. Appearance of Variations: Except the identical twins, no two individuals are similar and their requirements are also not exactly the same. It means there are differences among the individuals. These differences are called variations. Due to the variations some individuals would be better adjusted towards the surroundings than the others. Adaptive modifications are caused through the struggle for existence. According to Darwin, the variations are gradual (continuous) and those which are helpful in the adaptations of an organism towards its surroundings would be passed on to the next generation, while the others disappear. v. Natural Selection or Survival of the Fittest: The organisms which are provided with favourable variations would survive, because they are the fittest to face their surroundings, while the unfit are destroyed. Originally it was an idea of Herbert Spencer (1820-1903) who used the phrase ‘the survival of the fittest’ first time. Darwin renamed it as natural selection. It is to be noted that only survival of the fittest is not enough. But organisms should also adapt or change themselves according to the changed conditions of the environment as environment is always changing. To explain the phenomenon of natural selection, the extinct reptiles can be cited as an example. During the evolution of reptiles, giant reptiles, the dinosaurs etc., appeared. Majority of them were herbivorous, but due to certain climatic changes, the vegetation disappeared and, therefore, most of them became extinct. However, small animals who could change their feeding habits from herbivorous to carnivorous diet survived, because they could easily get adapted to the changed environment. This is how the nature selected the smaller reptiles over the larger ones. Darwin called it natural selection and implied it as a mechanism of evolution. vi. Inheritance of useful variations: The organisms after getting fitted to the surroundings transmit their useful variations to the next generation, while the non-useful variations are eliminated. Darwin could not differentiate between continuous and discontinuous variations. In this respect, Darwin agreed with Lamarck’s views, because according to Darwin acquired characters which are useful to the possessor could be inherited. vii. Speciation (Formation of new species): Darwin considered that useful variations are transmitted to the offspring and appear more prominently in succeeding generations. After some generations these continuous and gradual variations in the possessor would be so distinct that they form a new species. (NB: There are both Evidences in Favour and Objections against Darwin’s theory, Read them of your own.) 5.3 Mutation theory: Hugo de Vries (1848—1935), a Dutch botanist, put forward his views regarding the formation of new species in 1901. According to him, new species are not formed by continuous variations but by sudden appearance of variations, which he named as mutations. He believed that mutation causes evolution and not the minor heritable variations which were mentioned by Darwin. The salient features of mutation theory are:  Mutations or discontinuous variations are the raw material of evolution.  Unlike Darwin’s continuous variations or fluctuations, mutations do not revolve around the mean or normal character of the species.  All mutations are inheritable.  Mutations appear in all conceivable directions. Mutations are random and directionless while Darwin’s variations are small and directional.  Useful mutations are selected by nature. Lethal mutations are eliminated. However, useless and less harmful ones can persist in the progeny.  Accumulation of variations produces new species. Sometimes a new species is produced from a single mutation. 8   According to Darwin evolution is gradual while Hugo de Vries believed that mutations appear all of a sudden and hence known as saltation. i.e. Evolution is a jerky and discontinuous process. The major points in favour of the Mutation theory are: It can explain both progressive and retrogressive evolution which Darwin’s theory cannot. Further mutation theory can explain the simultaneous occurrence of both changed (new) and unchanged (wild) forms in nature. The major points against the Mutation theory are: Natural mutations are not very common as Hugo de Vries thought them to occur. Most of the mutations are negative or retrogressive. Mutations are generally recessive while traits taking part in evolution are usually dominant. 5.4 Hardy-Weinberg principle: It was proposed by G.H. Hardy, an English mathematician and W. Weinberg, a German physician independently in 1908. It describes a theoretical situation in which a population is undergoing no evolutionary change. The Hardy-Weinberg principle states that: 1. The gene pool (total genes and their alleles in a population) remains constant. 2. Allele frequencies in a population are stable and are constant from generation to generation. 3. Sum total of allelic frequency is one Hardy-Weinberg principle can be expressed binomially. Suppose individual frequencies p and q represent the frequency of allele A and allele in a diploid individual. The Genotypic frequency of AA individuals in a population is simply p2. This means that, the probability that an allele A with a frequency of p appears on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., p2. Similarly of aa is q2, of Aa 2pq. Hence, the sum total of genotypic frequency i.e. p2+2pq+q2=1. This is a binomial expansion of (p+q)2. This is called genetic equilibrium. Constant gene frequencies over several generations indicate that evolution is not taking place. Changing gene frequencies would indicate that evolution is in progress. In other words, evolution occurs when the genetic equilibrium is upset (evolution is a departure from Hardy-Weinberg Equilibrium Principle). N.B. Gene frequency is the frequency with which a particular allele occurs in a population. The term allele is employed for any two or more forms of a gene present on the same locus in the two homologous chromosomes. Five factors are known to affect Hardy-Weinberg equilibrium. These are:  Gene migration or gene flow: Gene flow refers to the movement of alleles from one population to another as a result of interbreeding between members of the two populations. Thus, when migration of a section of population to another place and population occurs, gene frequencies change in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population.  Genetic drift: Genetic drift is also known as “Sewell Wright Effect” (named after its discoverer). It occurs only by chance and only a small population is involved. It is non directional. Genetic drift can cause elimination of certain alleles or fixation of the other alleles in the population. Sometimes in case of a genetic drift the original drifted population is very different from the native population. Thus the drifted population establishes a new lineage and becomes founders and the effect is called founder effect.  Mutation: Both gene or chromosomal mutation lead to change in gene frequency in a population. 9   Ggenetic recombination: Crossing over during meiosis is a major source of genetic variation within population. Offspring formed from these gametes showing ‘new’ combination of characteristics are called recombinants. This also leads to change in gene frequency.  Natural selection: Natural selection also leads to change in gene frequency. Fig: Diagrammatic representation of Hardy- Weinberg’s equilibrium in a population for a particular phenotype: (a) Equilibrium condition (b) A stable population but, Nature has favoured a particular trait (Natural selection) (c) Irregular or Disruptive (population has recently faced some stress condition) (d) A directional change is happening in the population. 6. Geological time scale: The vast expanse of geological time has been separated into eras, periods, and epochs. The entire interval of the existence of visible life is called the Phanerozoic eon. The names of the eras in the Phanerozoic eon (the eon of visible life) are the Cenozoic ("recent life"), Mesozoic ("middle life") and Paleozoic ("ancient life"). The further subdivision of the eras into 12 "periods" is based on identifiable but less profound changes in life-forms. In the most recent era, the Cenozoic, there is a further subdivision of time into epochs. Eon (b.y.a) Era Period (m.y.a) Epoch (m.y.a) Events (b.y.a) Quaternary Holocene (0.01) Age of man and herbs Pleistocene (1.8) Tertiary Pliocene (5.3) Origin of human beings Cenozoic Miocene (23.8) First man like apes, Oligocene (33.7) Rise of monkeys, apes , monocots (0.14- Eocene (54.8 diversification of placental mammals today) and birds Paleocene Rise of primates and modern birds, (65.0) Phanerozoic Mesozoic Cretaceous (144) Age of Reptiles Extinction of Dinosaurs, Origin of and monocots (0.29- Jurassic (206) Gymnosperms Origin of angiosperms 0.14) Triassic (248) Rise of Dinosaurs, Origin of mammals Permian (290) Extinction of trilobites and many other marine animals, Origin of reptiles Paleozoic Carboniferous: Age of Rise of gymnosperms Pennyslvanian (323) Amphibians (0.54- Carboniferous: Rise of amphibians and seed ferns 0.29) Mississippian (354) Devonian (417) Origin of lung fishes and amphibians Age of Fishes Silurian (443) origin of ferns club mosses 10  Ordovician (490) Rise of corals, giant mollusks, first land Age of plants (bryophytes) Cambrian (540) invertebrates Abundant marine algae, bacteria, fungi trilobites and other invertebrates Proterozoic Evolution of eukaryotes, primitive invertebrates etc. The Huronian glaciation was a glaciation (2.5-0.54) that extended from 2.4 billion years ago (Gya) to 2.1 Gya, it is considered to be the 1st Ice Precambrian Age on earth. Archean Evolution of kingdom Monera (Age of invisible life) including archaebacteria, blue green (3.8 -2.5) algae Hadean Age of no life (4.6-3.8) 7. Mass extinctions Time periods in the history of life on Earth during which exceptionally large numbers of species became extinct are called mass extinctions. These extinctions are quite different from the normal rate of extinction. There have been five major mass extinctions events in the past and at present, 99.9 percent of all species that have existed on Earth are extinct. End Ordovician extinction (or known as Ordovician-Silurian extinction) occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted. During this extinction 25 percent of marine families and 60 percent of marine genera were lost. Late Devonian extinction took place somewhere around 364 million years ago. Its cause is unknown. However, evidences suggest that warm water marine species were the most severely affected in this extinction event. Thus, this suggests that the extinction of the Devonian was triggered by another glaciation event on Gondwana, which is evidenced by glacial deposits of this age in northern Brazil. Similarly to the late Ordovician crisis, agents such as global cooling and widespread lowering of sea-level may have triggered the late Devonian crisis. This mass extinction killed 22 percent of marine families and 57 percent of marine genera. End Permian extinction (or known as Permian-Triassic extinction) happened about 251 million years ago and was Earths worst mass extinction. 95 percent of all species, 53 percent of marine families, 84 percent of marine genera, and an estimated 70 percent of land species such as plants, insects and vertebrate animals were killed during this catastrophe. Direct evidence for this period has not been found but many scientists believe a comet or asteroid impact led to this extinction. Others think that volcanic eruption, coating large stretches of land with lava from the Siberian Traps, which are centered around the Siberian City of Tura, and related loss of oxygen in the seas were the cause of this mass extinction. End Triassic extinction (or known as Triassic–Jurassic extinction), occurred roughly 199 million to 214 million years ago, was most likely caused by massive floods of lava erupting from the central Atlantic magmatic province triggering the breakup of Pangaea and the opening of the Atlantic Ocean. The volcanism may have led to deadly global warming. Rocks from the eruptions now are found in the eastern United States, eastern Brazil, North Africa 11 and Spain. 22 percent of marine families, 52 percent of marine genera, and an unknown percentage of vertebrate deaths were the result. Cretaceous-Tertiary extinction (or known as Cretaceous–Paleocene extinction) occurred about 65 million years ago and is thought to have been aggravated, by impacts of several-mile-wide asteroid that created the Chicxulub crater now hidden on the Yucatan Peninsula and beneath the Gulf of Mexico. Yet, some scientists believe that this mass extinction was caused by gradual climate change or flood-like volcanic eruptions of basalt lava from the Deccan Traps in west-central India. During this extinction, 16 percent of marine families, 47 percent of marine genera, and 18 percent of land vertebrate families including the dinosaurs became extinct. The Sixth Mass Extinction has already begun! (Quaternary mass extinction) The sixth mass extinction is in progress, now, with animals going extinct 100 to 1,000 times (possibly even 1,000 to 10,000 times) faster than at the normal background extinction rate, which is about 10 to 25 species per year. Many researchers claim that we are in the middle of a mass extinction event faster than the Cretaceous-Tertiary extinction which wiped out the dinosaurs. Rather than a meteorite or large volcanic eruption, the alarming decline of biodiversity (diversity of species on earth) leading to the current mass extinction is the results of five major human activities:  Habitat destruction including human-induced climate change.  Invasive species. (Invasive species displace native species through predation, competition, and disease.)  Pollution.  Human overpopulation.  Over-harvesting (hunting, fishing, and gathering). 784 species of plants and animals have recently vanished from earth because of human activities which includes the Hawai's chaff flower, the golden coqui Puerto Rican tree frog, the Martinique Parrot, the Yuman box turtle, the Madagascan Pygmy hippo, the Japanese sea lion and many more. All continents are impacted by this ongoing biological catastrophe. 8. Brief account on evolution of Human Primates, like humans, are mammals. Around sixty to forty million years ago, the ancestral primate lineage split through speciation. This splitting lead to the evolution of variety of species we see today. 12 Primates have been present for 65 million years (end of Mesozoic era) and are defined by characteristics shaped by natural selection for living in trees. Characteristics of Primates: - Limber shoulder joints which make it possible to brachiate. - Dexterous hands for hanging on branches and manipulating food. - Sensitive fingers with nails, not claws. - Opposable thumb and 4 fingers. - Eyes are close together on the front of the face, giving overlapping fields of vision for enhanced depth perception (binocular vision). - Excellent eye-hand coordination. - Parental care with usually single births and long nurturing of offspring. - Poor sense of smell Prosimians (non-anthropoid primates) lemurs, lorises, etc. Tree shrews, the first to diverge from the primitive primate lineage, Mostly nocturnal Anthropoids include all other primates. - Fossils of monkey-like primates indicate anthropoids were established in Africa and Asia by 45 million years ago (S. Amer. and Africa were separated) - Primates became diurnal about 36 million years ago - Refinement of opposable thumb * The New World monkeys, some with prehensile tails spider monkeys, capuchins, and squirrel monkeys, are all arboreal, nostrils open to the side, a few have lost opposable thumb 13 Ancestors of New World monkeys may have reached South America by rafting from Africa or migration southward from North America. * The Old World monkeys, mandrills, baboons, macaques and rhesus monkeys nostrils open downward arboreal and ground-dwelling forms, none with prehensile tails * Hominoids: hominids and apes - Hominids: humans and their direct ancestors. Homo sapiens are the only living hominid. -The lesser apes are most divergent from humans and include the gibbons of Southeast Asia. They are small and move primarily by brachiation. -The great apes are our closest relatives. These include orangutans (genus Pongo), gorillas (genus Gorilla), and chimpanzees (genus Pan), our closest relative Evolutionary Origins of Humans. 5-8 mya Trends in hominid evolution: - Bipedalism - the location of the foramen magnum (where the spinal cord enters the skull). - shape of the pelvis - curvature of the spine - first toe opposable or not - Increased brain size) and Reduction in brow ridge -The dental arch of hominids is paraboloid (an arch); that of great apes is U-shaped -Flattening of face -More refined hand movements (precision and power grips) -Decrease in sexual dimorphism Examples of Fossil records: Sahelanthropus tchadensis discovered in 2001 in Chad - between 6 and 7 myo. Not certain if it is a hominid or more kin to apes. Face much flatter but not certain at this point if it was fully bipedal. Significant also because found much further west in Africa than any other hominid fossil. Orrorin tugenensis (about 6 mya) Ardipithecus ramidus (Australopithecus ramidus) (4.4 - 4.2 mya). Fossil. Australopithecines: (southern ape) The First Humans: 4.4 - 1.1 mya. Australopithecus anamensis. (4.2 - 3.9 myo). Australopithecus afarensis. (3.7 - 2.8 myo) "Lucy" about 3.2 myo. Skull. Found in Ethiopia in Afar region in 1974. Kenyanthropus platyops (3.5 myo). It lived about the same time as A. afarensis, but has a flatter face and smaller teeth, appearing more similar to modern humans than did A. afarensis. The skull was found on the shores of Lake Turkana in Kenya. Australopithecus africanus (3 - 2 myo). Skull. First hominid fossil found. Australopithecus garhi (2.5 myo) - possibly first tool user. Found in Ethiopia with shaped tools. Australopithecus boisei (2.3 - 1.4 myo). Australopithecus robustus (1.9 - 1.5 myo). 14 Homo spp. 2.4 myo to present. Significantly larger brain size than australopithecines. Homo habilis "handy man" (2.5 - 1.6 myo). Skull. Once thought to be the first tool user. Broca's area developed. Homo rudolfensis (2.4-1.8 myo). Skull. May be larger habilis. Homo ergaster similar to Homo habilis but larger. Homo erectus (1.8 myo to perhaps 250,000 years ago). First with evidence that they used fire. Homo floresiensis (95,000 and 13,000 years ago) Homo heidelbergensis (800,000 - 100,000 years ago) - may have led to sapiens or neandertalensis. Homo neanderthalensis (some consider as Homo sapiens neanderthalensis) (230,000 - 30,000 years ago) Neanderthals. Homo sapiens (modern) (100,000 years ago to present). Cro-Magnon Dispersal Pattern in Human Evolution The Multiregional Hypothesis The Out-of-Africa or Replacement Hypothesis 15  Out of Africa Theory Solve the following Problems related to Hardy-Weinberg Equilibrium 1. The frequency of two alleles in a gene pool is 0.19 (A) and 0.81(a). Assume that the population is in Hardy-Weinberg equilibrium. (a) Calculate the percentage of heterozygous individuals in the population. (b) Calculate the percentage of homozygous recessives in the population. 2. An allele W, for white wool, is dominant over allele w, for black wool. In a sample of 900 sheep, 891 are white and 9 are black. Calculate the allelic frequencies within this population, assuming that the population is in H-W equilibrium. 3. In a population that is in Hardy-Weinberg equilibrium, the frequency of the recessive homozygote genotype of a certain trait is 0.09. Calculate the percentage of individuals homozygous for the dominant allele. 4. In a population that is in Hardy-Weinberg equilibrium, 38 % of the individuals are recessive homozygotes for a certain trait. In a population of 14,500, calculate the percentage of homozygous dominant individuals and heterozygous individuals. 5. In a population that is in Hardy-Weinberg equilibrium, if 160 out of 200 individuals are Rh+, calculate the frequencies of both alleles. (Note:: In humans, the Rh factor genetic information is inherited from our parents, but it is inherited independently of the ABO blood type alleles. In humans, Rh+ individuals have the Rh antigen on their red blood cells, while Rh− individuals do not. There are two different alleles for the Rh factor known as Rh+ and rh. Assume that a dominant gene Rh produces the Rh+ phenotype, and that the recessive rh allele produces the Rh− phenotype.) 16 Suggested Books for further readings: 1. The History of Life on Earth: The story of evolution on our planet by Nathan Keighley 2. History of Life by Richard Cowen 3. Organic Evolution (Evolutionary Biology) by Veer Bala Rastogi 4. Brock Biology Of Microorganisms, by Madigan Michael T. , Martinko John M. , et al. 5. Understanding Earth by Grotzinger, Jordan, Press & Siever 17