Download IGNOU ENVIRONMENT AND ECOLOGY and more Lecture notes Ecology and Environment in PDF only on Docsity!
APPENDIX-C
CURRICULUM OF SENIOR SECONDARY COURSE
IN ENVIRONMENTAL SCIENCE (333)
RATIONALE
Rapid growth of population coupled with increasing industrial development and all around increase in consumerism throughout the world are posing a serious threat to the environment. People in almost all nations of the world are becoming increasingly conscious of the danger of deteriorating environmental conditions. In view of the critical importance of the environmental issues, it is necessary to introduce Environmental Science as a full-fledged subject at the Senior Secondary level. Environmental Science deals with the relationships between environment and humans and draws upon physical sciences, biological sciences and social sciences.
Humans have been concerned with environment since the beginning of civilization. Even our ancient scriptures have emphasized the virtues and values of environmental conservation. Now, it is even more critical than ever before for mankind to have a better understanding of environmental issues to promote sustainable development practices. Environmental science embraces problems related to conservation of natural resources, deforestation, loss of biodiversity, environmental pollution, deterioration of life support systems and issues like global warming, ozone depletion etc. All this and much more is dealt within the subject.
The course covers all the major components of the environment including natural resources, ecological principles and population dynamics, pollution, wildlife conservation, and impact of industrialization. In
addition, it also addresses environment related socio-economic, cultural and ethical aspects, which are important to ensure a sustainable future for humans. The course also provides practical insight into environmental management to enable an appreciation of the issues related to sustainable livelihood and human welfare.
OBJECTIVES The course is designed to enable the learner: l to know about origin of earth and evolution of life, and appearance of human species;
l to develop concerns for environmental problems;
l to understand ecological principles.; l to harmonize environmental concerns with technological and socio-economic issues; l to develop respect for nature and living beings and to help maintain ecological balance; l to take active part in protecting and conserving the environment and to assume the responsibilities for change of society;
COURSE STRUCTURE
The present curriculum contains 7 Core modules and 2 Optional modules. The Core modules are com- pulsory for all learners, whereas the learner can choose any one of the two Optional modules. Thus, each learner goes through eight modules in all. Each module has been divided further into units and then into lessons. The number of lessons, suggested study time and marks allotted for each unit are as follows:
They will also learn about the use of natural resources by primitive humans and evolution of the socio-cultural environment. The learner will also visualize how industrial development has led to environmental degradation and realise that such degradation poses a threat to human well being and survival of other living beings.
Module–1: Environment through Ages
Time: 15 Hours Marks: 05
Approach
This module is intended to enable the learners to visualize the origin of earth and the development of conditions for support of life.
Unit wise Distribution of Core Modules Number Study Marks allotted of lessons hours Unit Module Module 1 : Environment through Ages 1.1 Environment-Origin, Evolution of Environment 3 15 5 05 and its uses by Humans Module 2 : Ecological Concept and Issues 2.1 Principles of Ecology : Composition and various 4 30 12 12 types of Ecosystem Module 3 : Human Impact of Environment 3.1 Human Settlements and their impact on 2 20 07 07 Environment Module 4 : Contemporary Environmental Issues 4.1 Environmental Pollution and Natural Disasters 3 25 10 15 4.2 National and Global Environmental Issues 2 15 05 Module 5 : Environmental Conservation 5.1 Conservation of Biodiversity and other Natural 4 35 14 14 Resources (Soil, Land, Water, Energy etc.) Module 6 : Sustainable Development 6.1 Sustainable development with regard to 4 20 07 07 Agriculture and Cleaner technology Module 7 Environmental Management 7.1 Environmental Ethics 1 5 2 8 7.2 Legislation for Environmental Improvement 2 10 4 7.3 Organization devoted to Environment 1 5 2 Optional Module 8A : Water Resource Management 8.1 Water as a Resource 3 18 07 12 8.2 Conservation of water 2 12 05 Or Optional module 8B : Energy and Environment 8.1 Energy use and its Impact on Environment 4 18 07 12 8.2 Energy Conservation 1 12 05 Theory examination 31 3 hrs 1 paper 80 Practical Examination 3 hrs 1 paper 20 Total 100
l Food chain and food web
i. trophic levels – producer, consumer, decomposer ii. ecological pyramids
iii. energy flow in a food chain
l Energy efficiencies
l Nutrient cycles (water, carbon, nitrogen)
Supportive Audio-Video Programme
l Ecological pyramids
l Nutrient cycles
2.1.3 Natural Ecosystems
l Terrestrial ecosystems
l Threatened ecosystems and causes thereof
l Aquatic ecosystem with Indian examples
i. fresh water
ii. marine
l Ecotones and edge effect
Supportive Audio-Video Programme
l Ecosystems – natural and human modified
l India’s threatened ecosystems
2.1.4 Human Modified Ecosystem
l Agro-ecosystems
l Plantation forests
l Dams and reservoirs
l Aquaculture ponds
l Urban and industrial ecosystem
Module–3: Human Impact on Environment
Time: 20 Hours Marks : 07
Approach
This module is designed to enable the learner to understand the varieties of problems that have
arisen due to increasing human habitations in the form of cities. The module also covers the highly important aspects of deforestation, loss of biodiversity.
Unit 1 Human Settlements and their impact of Environment
3.1.1 Human Societies
l Rural settlements
i. Characteristics of rural settlement
ii. Land use changes
iii. Effect of modern technology on agriculture
iv. Environmental problems of rural areas
l Urban settlements
i. Urban settlement – its occurrence, push and pull factors
ii. Life style – changing life patterns
iii. Slums and urban planning
iv. Increased resource consumption
v. Increased waste generation (liquids, solid and gases)
3.1.2 Deforestation
l Causes of Deforestation i. Increase in human population ii. Transformation forests into agricultural fields iii. Overexploitation of forest resources
iv. Urbanization and industrialization l Consequences of Deforestation i. Soil erosion ii. Depletion of wildlife iii. Floods iv. Effect on climate
v. Desertification
l Loss of Biodiversity
i. Causes of biodiversity loss
ii. Threatened/endangered/rare species
iii. Invasion of exotic species
iv. Consequences of biodiversity loss
l Effect on tribal societies
Supportive Audio-Video Programme
l Biodiversity
l Deforestation
l Desertification
l Wildlife conservation
Module–4: Contemporary Environmental Issues
Time: 40 Hours Marks: 17
Approach
This module brings about awareness of the contemporary environmental issues related to natural and man-made problems. Major national and global environmental issues have been described in this module to familiarize the learner with environmental pollution and natural disasters. Environment related human health problems are also highlighted in this module.
Unit 1 Environmental Pollution and National Disasters
4.1.1 Pollution – Its causes, consequences and prevention
l Air and Noise pollution
l Water pollution
l Soil pollution
l Thermal pollution
l Radiation pollution
Supportive Audio-Video Programme
l Pollution-air, water, noise, soil
l Uses and effects of pesticides and insecticides 4.1.2 Environment and Health
l Water borne diseases
l Air pollution and health
l Environmental carcinogens
l Heavy metals (arsenic, mercury and lead) toxicity
l Occupational health
Supportive Audio-Video Programme
l Environment and human health
4.1.3 Disasters and their Management l Types of disasters – natural and human-made
l Causes and management of the following types of disasters
i. Water and climate related disasters – Flood, cyclone, drought
ii. Earthquake
iii. Accident related disasters – Forest fire, oil spill,
l Biologically related disasters – Epidemics (Dengue, SARS, HIV, mad cow disease and bird flu), pest attacks, cattle epidemics
Supportive Audio-Video Programme
l Disaster-its causes and management
Unit-2 National and Global Environmental Issues
4.2.1 National Environmental Issues
l Growth of human population – size, growth, density, dispersion, age (shift in the population growth curve with special reference to ageing population) and sex ratio, natality and mortality, immigration, emigration
5.1.4 Land Conservation
l Causes, consequences and control of land degradation
l Methods of land reclamation and conservation
Supportive Audio-Video Programme
l Conservation of land
5.1.5 Energy Conservation
l Conventional and non-conventional sources of energy
l Efficient use of energy – in home, place of work, transport and industry
l Renewable energy programme in India
Supportive Audio-Video Programme
l Conservation of energy
5.1.6 Water Conservation
l Causes of water degradation and scarcity
l Methods of conserving water resources
l Methods of preventing water degradation and control of water pollution
Module–6: Sustainable Development
Time: 20 Hours Marks: 07
Approach
This module aims to inform the learner about the concept of sustainable development for integrating environmental conservation with developmental objectives. This module elaborate the concept of sustainable agriculture including crop rotation, genetic control, organic agriculture, integrated pest management and cleaner technology.
Unit 1 Sustainable Development with regard to Agriculture and Cleaner Technology
Concept of Sustainable Development
l Our common resources and tragedy of commons
l Development without destruction
l Safeguarding resources for future generations
l Ensuring equity and transgenerational consideration Supportive Audio-Video Programme l Sustainable development-concept
Modern Agriculture l Green revolution l Agricultural impacts and environmental degradation (pesticides, fertilizers) l Animal husbandry l Management of livestock and their environmental consequences- examples (foot and mouth diseases)
l Consequences of practices used for enhancing animal and plant production – hormones, steroids, and fish culture Supportive Audio-Video Programme l Green revolution l Animal husbandry Concept of Sustainable a Agriculture
l Approaches of sustainable agriculture l Crop rotation l Genetic improvement including GMOs l Integrated Pest management (IPM) l Biofertilizers (Cyanobacteria)
l Organic Farming Supportive Audio-Video Programme
l GMOs l Crop rotation l Organic farming l Biofertilizers : uses and effects 6.1.2 Cleaner Technology
l The concept of cleaner technology
l Agriculture life cycle analysis
l Waste management
i. Industrial wastes : reduce, recycle and reuse
ii. Domestic wastes : reduce, recycle and reuse
Supportive Audio-Video Programme
l Cleaner Technology and Waste Management
Module–7: Environmental Management
Time: 25 Hours Marks: 08
Approach
This module aims to inform learner about the concept of environment impact assessment and its relevance for promoting environ-friendly development. The learner will also be introduced to various national and international legislation promulgated for environmental improvement and conservation. This module also highlights the need to respect all life forms, ethics and Gandhian approach towards environment conservation.
Unit 1 Legislations for Environmental Improvement and Conservation
7.1.1 Environmental Legislation
l Need for legislation
l National legislation
i. Pollution related Acts
- Water Pollution Act
- Air Pollution Act
- Environment Act ii. Biodiversity related Acts
- Forest Act
- Biodiversity Act iii. International legislations/conventions
i. Wetland Convention
ii. Montreal Protocol
iii. Climate Convention
iv. Biodiversity Convention
Supportive Audio-Video Programme
l Environmental legislation – national and international
7.1.2 Environmental Impact Assessment (EIA)
l Negative impact of development projects – concept of externality
l Development without destruction
l Anticipation and mitigation of negative impact of development projects
l Requirement for environment impact assessment
l Methods of carrying out environment impact assessment
l Environment impact assessment practices in India
l Evaluation of alternative scenarios
Unit 2 Organisation related to Environment
7.2.1 Environment related Institutions and Organizations
l National Environmental Agencies
i. Ministry of Environment and Forests (MoEF)
ii. State Environment Bodies
iii. Central Pollution Control Board (CPCB)
iv. State Pollution Control Board (SPCB)
v. Indian Board for Wildlife (IBW)
l International Environmental Agencies
i. United Nations Environmental Programme (UNEP)
ii. World Health Organisation (WHO)
l Importance of water
8.1.2 Ground Water Resource
l Use and management
l Importance of ground water
l Ground water recharging – natural and human made depletion of ground water
l Depletion of water resources
Supportive Audio-Video Programme
l Depletion of ground water resources
8.1.3 Fresh Water Resource and Distribution
l Distribution of fresh water resources
l Domestic, agricultural and industrial use of water
l Obtaining, processing and distribution of drinking potable water at community levels-water supply
Unit-2 Conservation of Water
8.2.1 Methods of Water Harvesting
l Need of water harvesting
l Traditional methods of water harvesting
l Modern methods of water harvesting
Supportive Audio-Video Programme
l How can we conserve our water resources for future generations
8.2.2 Conservation at different levels
l Water shed management (prevent wastage and control of pollution)
l Role of an individual in water conservation
OPTIONAL MODULE – 2
Energy and Environment
Time: 30 Hours Marks: 12
Approach
This module exposes the learner to the vital area of energy and both its renewable and non-
renewable sources. The learner is also exposed to the concept of alternative sources of energy apart from the traditional ones. The learner is also told about the impact of energy use on environment. A good deal of emphasis is laid on the need and methods of conservation of energy.
Unit-1 Energy use and its impact on Environment
8.1.1 Importance of Energy in Society
l Importance of energy of doing work
l Interrelationships between energy and development
l Laws of energy
l Impact of energy use on environment along with case studies
l Constraints in energy generation, supply and transmission
Supportive Audio-Video Programme
l Uses of energy in daily life
8.1.2 Non-renewable Sources of Energy
l Definition
l Fossil fuels : coal, petroleum, natural gas
l Nuclear plant
l Naphtha
l Lignite
l CNG as a cleaner fuel
8.1.3 Renewable Sources of Energy – 1
l Definition
l Solar energy : solar cooker, solar heater, solar cell
l Wind energy
l Hydro energy
l Thermal energy
8.1.4 Renewable Sources of Energy –
l Biomass
l Biogas energy
l Animal energy
l Geothermal energy
l Hydrogen energy
l Fuel cell technology
Supportive Audio-Video Programme
l Various sources of energy
Unit – 2 Energy Conservation
8.2.1 Energy Conservation
l At household level
l At community level
l At work place, in transportation and building construction
l Design of energy efficient new towns
l Energy efficient devices
l Concept of energy auditing
Supportive Audio-Video Programme
l Energy conservation at various levels
PRACTICAL WORK
The purpose of teaching Environmental Science is not only to acquaint the learner with theoretical knowledge but also to develop practical skills. Development of these skills leads to better understanding of the environment through hands-on experience and mutual reinforcement of theory and practice. Field exercises and laboratory work develop psychomotor skills. The present course involves field work, laboratory exercises and short innovative projects to exercise creative thinking and problem solving skills. The list of practical exercises to be carried by a student as part of this course on Environmental Science is given below:
A. FIELD STUDIES (ANY THREE)
- Study a simple ecosystem (suggested habitats- pond, river, estuarine, lake, grassland, forest, and desert) and describe the biotic and abiotic components of the ecosystem.
- Study of the effect of human interactions with the natural environment.
- Survey of vegetation, birds, insects and other animals in your locality.
- Choose five common tree species plants from your neighbourhood and list their common names. Describe each plant in terms of its height and leaf characteristics.
- Describe the environmental problem of your locality and suggest their remedy.
- Visit to different water bodies in your village/ locality and describe their uses and source of water pollution. If any
- To segregate domestic solid waste into biodegradable and non-biodegradable components.
LABORATORY EXERCISES ( ALL )
- Study of water quality.
- Soil texture and analysis of components.
- To estimate dust (particulate) deposition on the leaves of road side plants.
- To study the effect of light intensity on the growth of plants. C. CREATIVE ACTIVITIES (ANY TWO)
- Set up an aquarium.
- To study the biodiversity birds and insects in your locality.
- To prepare a list of plants and animals which are used as food for humans and to comment on their habit and habitat.
1
Notes
MODULE - 1
Environment through Ages
Origin of Earth and Evoluation of the Environment
ORIGIN OF EARTH AND EVOLUTION OF
THE ENVIRONMENT
We live on a beautiful planet called earth, along with a wide variety of plants, animals and other organisms. Our earth, however, is part of a vast universe. The universe is about 15 to 20 billion years old. The age of the earth is approximately 4 to 5 billion years, while human beings evolved only around 2 million years ago. In this lesson, you shall learn how the earth originated, how it got its own environment and in what ways human beings have been using the environmental resources for their welfare and development.
OBJECTIVES
After completing this lesson, you will be able to:
- trace the origin of the earth;
- list the conditions, which make the earth a unique planet for supporting life;
- describe the sequence of steps in the origin and evolution of life prior to the appearance of humans;
- explain the term environment;
- enumerate the various biotic and abiotic constituents of the environment.
1.1 EARTH AS PART OF THE UNIVERSE AND THE
SOLAR SYSTEM
Our earth, with all its diversity alongwith other planets and their satellites, the sun, the moon, the many galaxies (huge groups of millions of stars) form the universe. There are also countless asteroids and comets in orbit around the sun. All these are also part of the universe. It extends much farther than can be seen by the most powerful telescope. No one knows where the universe ends.
Environmental Science Senior Secondary Course
Notes
2
MODULE - 1
Environment through Ages When you look up at the sky on a clear night, you see many points of light – most of which are stars. Stars are huge balls of bright, hot glowing gases. The ‘Sun’ is also a star. It is the star nearest to earth – about 150 mk (million kilometers) away. A solar system consists of a star in the middle with a number of planets orbiting around it. The earth is a part of its solar system. It is one of the eight planets of the solar system that has the sun (a star) in the middle and the eight planets moving around it. Until recently solar system was believed to have nine planets. However, on the basis of the latest scientific assessment, Pluto, is no longer regarded as a planet of earth’s solar system. (Fig. 1.1)
Fig. 1.1: Planets orbiting the sun
1.2 ORIGIN OF THE UNIVERSE AND ORIGIN OF THE
EARTH
The widely accepted theory of the origin of universe is the “BIG BANG” theory. According to this theory, universe started with a huge explosion and matter (dust and gases) filled the entire space. The temperature of the universe then, was about hundred billion degrees Celsius. Scientists believe that the big bang occurred about 15 to 20 billion years ago. The huge collection of dust and gases then began to spin. As it spun faster and faster, the centre became very hot. It became the Sun. From the edges of this ball of dust and gas, big blobs or chunks of dust broke off and formed eight ball shaped planets. This founded our solar system (Fig. 1.2). The earth broke off about 4.5 billion years ago with an explosion. It was a burning hot white mass of gas and dust. Over a long period of time, dust and gas gradually condensed to form solid rock. Such condensation and shrinking made the earth heat up so much that the rock melted into a gluey liquid. After millions of years, the outer surface of the earth or the earth’s crust cooled and formed hard rock again, just as melted chocolate or wax solidifies upon cooling. The interior of the earth is still very hot.
Sun
Environmental Science Senior Secondary Course
Notes
4
MODULE - 1
Environment through Ages As you already know, once every 24 hours, the earth rotates on its axis like a spinning top. So the day and night cycle is of 24 hours. A planet’s axis is an imaginary line passing through the centre of the planet. (Fig. 1.3b). The earth not only rotates around its axis but also revolves around the sun. The earth completes one full circle around the sun or completes one orbit of the sun in 365¼ days. An orbit is the path along which a planet moves around the sun.
While earth revolves around the sun, moon orbits the earth. The moon completes one orbit in 27.33 days. The moon, as we know today, is without water and air and life. From the space, the earth looks like a beautiful bright bluish planet because of its blue oceans.
INTEXT QUESTIONS 1.
- Approximately how old is the earth?
- Name the star around which the earth revolves along with other planets of the solar system.
- What do you mean by “solar system”?
- Why does the day and night cycle consist of only 24 hours?
- If you were to view earth from space, which colour would earth reflect?
1.3 EARTH–THE UNIQUE PLANET WHICH SUSTAINS
LIFE
In our solar system, earth is the only planet which is known to sustain life. Only earth has air and water to support life. Let us briefly review the conditions on the other seven planets of the solar system.
- Mercury (Buddha) is closest to the sun. It has a temperature range of 427ºC on its side facing the Sun and – 270ºC, on its dark side. It has no atmosphere.
- Venus (Shukra) is the closest neighbour of the earth. It is about 40 mk away. It is an extremely hot planet with a temperature of 480ºC. Its atmosphere has 96% carbon dioxide and poisonous gases like sulphur dioxide and carbon monoxide.
- Mars (Mangal) is also close to earth. It is called the red planet. It has 95% carbon monoxide and reddish dust. It is relatively a very cold planet and as of now presence
5
Notes
MODULE - 1
Environment through Ages
Origin of Earth and Evoluation of the Environment
of life on it has not been conclusively established.
- Jupiter (Brahaspati) is the largest planet of the solar system. It is mainly a rapidly spinning ball of gas specially clouds of ammonia, and has no solid surface.
- Saturn (Shani) consists mainly of hydrogen and helium. Its atmosphere has 90% nitrogen and a temperature of (-184ºC). It is also made up of hydrogen cyanide which is a highly poisonous gas. It is characterized by a ring that surrounds it.
- Uranus (Arun) is also a very cold planet. Uranus is a distant planet of solar system and 7th^ in order from the sun. Uranus and Neptune are the outermost planets of the solar system. Uranus has a highly tilted rotational axis.
- Neptune (Varun) is much smaller than earth, cold and dark with its surface coated with frozen methane.
- Earth is the only planet known to sustain life.
Scientists do not know of any other planet in the universe besides the earth, where there is life. There are hundreds of stars in the universe and they have planets orbiting round them. But whether the necessary conditions to support life exist there is not known.
As compared to other planets mentioned above, earth has the following unique conditions which have enabled it to sustain life.
1.3.1 Conditions necessary for sustaining life
a. Presence of water
As already mentioned, during the evolution of the earth, water vapour in the primitive atmosphere condensed into liquid water. This gave rise to the formation of oceans, rivers and other fresh water bodies. Three-fourth of earth’s surface is covered with water.
Water is a universal solvent and life originated in water. Two thirds of a living organism consists of water and 90 percent of cell content is also water. Biochemical reactions in living organisms require an aqueous medium. Therefore, water is important for the survival of living organisms.
b. Atmosphere
The earth is enveloped by a gaseous atmosphere that supports life. The earth’s atmosphere consists of nitrogen (78%) and oxygen (21%), small amounts of carbon dioxide, water vapour, ozone and rare gases like argon, neon etc.
Oxygen from the atmosphere is used by the living organisms during respiration. Oxygen is necessary to oxidize food for liberating energy required for various activities in the living organisms. Green plants utilize carbon dioxide from the atmosphere during photosynthesis.
Neptune
Uranus
Saturn
Jupiter Mars Earth Venus Mercury Sun
Fig. 1.4: Our solar system
7
Notes
MODULE - 1
Environment through Ages
Origin of Earth and Evoluation of the Environment
- From where earth gets energy?
- Why oxygen is essential for life?
1.4 ORIGIN AND EVOLUTION OF LIFE PRIOR TO THE
APPEARANCE OF HUMAN BEINGS
To begin with, conditions on earth were inhospitable for life. Gases of the primitive atmosphere were primarily methane, ammonia, carbon dioxide and hydrogen. Water vapour filled the atmosphere but there was no free oxygen. It was thus a reducing atmosphere on primitive earth and no life existed.
Biological evolution- from the simple organisms to complex organisms
As earth cooled, water vapour condensed to form liquid water. Rains poured to form water bodies on earth. The molecules of life were formed in the water.
From the molecules of the life evolved bacteria, the earliest and simplest organisms. The oldest fossils of bacteria which were the first living organisms on earth have been found in rocks that are 3-5 billion years old.
For almost two billion years, different kinds of bacteria lived on earth. One of these evolved a green pigment called chlorophyll. These chlorophyll-containing bacteria used carbon dioxide and water and released oxygen through photosynthesis and started accumulating in the atmosphere.
Fig. 1.6: Diagrammatic representation of major events of life on earth (mya = millions of years ago)
No life
Millions of years before present 600 1000 mya
2500 mya
3,500 mya
5000 mya
(Reducing atmosphere)
Similar to those living today evolve
0
Environmental Science Senior Secondary Course
Notes
8
MODULE - 1
Environment through Ages
RELATIVE TIME SPAN OF ERAS
THE GEOLOGICAL TIME SCALE
Era Period Epoh Age Some important (million events in the year) history of life Recent 0.01 Historic time Quaternary Pleistocene 1.8 Ice ages; humans appear Pliocene 5 Ape like ancestors of humans appear Miocene Continued radiation of mammals and Cenozoic 23 angiosperms Oligocene Origins of most modern mammalian orders, Tertiary 34 including apes Eocene Angiosperm dominance increases; 57 further increase in mammalian diversity Paleocene Major radiation of mammals, birds, 65 and pollinating insects Cretaceous Flowering plants (angiosperms) appear; dinosaurs 144 and many groups of organisms become extinct Mesozoic Jurassic Gymnosperms continue as dominant plants; 208 dinosaurs dominant first birds Triassie Gymnosperms dominate landscape; 245 first dinosaurs and mammals Radiation of reptiles, origin of mammal-like Permain reptiles and most modern orders of insects; extinction of many marine invertebrates 285 Extensive forests of vascular plants; Carboniferous first seed plants; origin of reptiles; Paleozoic 360 amphibians dominant Devonian Diversification of bony fishes; 408 first amphibians dominant Siturian Diversity of jawless vertebrates; colonization of land 438 by plants and arthropods; origin of vascular plants Ordovician First vertebrates (jawless fishes); 505 marine algae abundant Cambrian Origin of most invertebrate phyla; 544 diverse algae 700 Origin of first animals 1500 Oldest eukaryotic fossils Precambrian 2500 Oxygen begins accumulating in atmosphere 3500 Oldest definite fossils knows (prokaryotes) 4600 Approximate origin of Earth
Cenozoic Mesozoic Paleozoic
Precambrian
Continued photosynthesis by such bacteria progressively accumulated oxygen in the atmosphere. Thus the atmosphere gradually transformed from reducing to oxidizing. At one point of time oxygen content in the atmosphere become 21%. Such changes served as a big trigger for biological evolution to begin and progress and this led to the invasion of land by living organism.
As time passed, protists evolved from bacteria. Both bacteria and protists are unicellular. Then came multicellular organisms, the fungi followed by plants and animals. Today the diversity of living organisms is comprised of five kingdoms of life. Monera, Prototictista, Fungi, Plantae and Animalia.
Fig. 1.7: Geological time scale
