National Year 12 Environmental Science
Chapters: 3
1. 3.1 The living environment
3.1.1 Conditions for life on Earth · 3.1.2 Conservation of biodiversity · 3.1.3 Life processes in the biosphere and conservation planning
- Evolution: Origin of Life, Mechanisms and Human Evolution – Life began on the early Earth from simple chemicals: Oparin and Haldane proposed it and Miller made amino acids in a flask. Evidence of evolution comes from fossils, homologous and analogous organs, embryos, molecules and changes we can watch (industrial melanism, drug resistance). Darwin explained it by natural selection acting on variation in populations; the modern synthetic theory adds genes: mutation, recombination, gene flow, genetic drift and natural selection change allele frequencies. If none of these act, frequencies stay constant: Hardy–Weinberg, p² + 2pq + q² = 1. Selection can be stabilising, directional or disruptive. One ancestor spreading into many habitats gives adaptive radiation (Darwin’s finches, Australian marsupials). Humans evolved from Dryopithecus-like apes through Australopithecus, Homo habilis, Homo erectus and Neanderthals to Homo sapiens.
- Biodiversity and its Conservation – Biodiversity is the variety of life at three levels: genetic, species and ecological. It is highest near the equator and grows with area (log S = log C + Z log A). Every species matters, like rivets on a plane. We are losing species fast because of the 'evil quartet': habitat loss and fragmentation, over-exploitation, alien species invasions and co-extinction. The IUCN Red List (Red Data Book) ranks species from Least Concern to Extinct. We protect life in situ (hotspots, national parks, sanctuaries, biosphere reserves, sacred groves, Ramsar wetlands) and ex situ (zoos, botanical gardens, seed and gene banks).
2. 3.2 The physical environment
3.2.1 The atmosphere · 3.2.2 The hydrosphere · 3.2.3 Mineral resources · 3.2.4 Biogeochemical cycles · 3.2.5 Soils
- Climate Change and the Greenhouse Effect – Climate is the average weather of a place over about 30 years. Greenhouse gases like carbon dioxide and methane trap some of the heat the Earth gives off. Humans have added a lot more of these gases by burning fossil fuels and cutting forests, so the Earth is warming. This causes melting ice, rising seas and more extreme weather. We can cut emissions (mitigation) and prepare for changes (adaptation).
- Water Resources and the Hydrosphere – Almost all of Earth's water is salty sea water. Only about 1% is liquid fresh water we can easily use, from groundwater, rivers and lakes. People often take water faster than nature refills it: aquifers fall, rivers run dry and wetlands shrink. Sustainable management means using no more than the recharge, sharing water fairly and keeping it clean. The ocean itself moves heat around the planet through thermohaline circulation, driven by differences in temperature and salt. Dirty water can be made safe by screening, settling, filtering and disinfecting. New sources include desalination, water reuse and rainwater harvesting, while saving water cuts demand.
- Mineral and Energy Resources of India (Class 12) – Minerals are natural substances with a fixed make-up. Most of India's minerals lie in old plateau rocks, in three belts: the north-eastern plateau, the south-western plateau and the north-western belt. Metallic minerals include iron ore, manganese, bauxite and copper; mica is a non-metallic mineral. Coal, petroleum and natural gas are conventional energy that will run out. Nuclear, solar, wind, tidal, geothermal and bio-energy are non-conventional and cleaner. Because minerals are non-renewable, we must use less, recycle scrap and use substitutes.
- The Carbon Cycle: Where Carbon Is Stored and How It Moves – Carbon moves between the air, living things, soil, oceans and rocks. These places are called stores (or sinks and sources), and the movements are called flows (fluxes). Photosynthesis takes carbon dioxide out of the air; respiration, decomposition and burning put it back. The ocean takes in and gives out huge amounts. Over millions of years carbon is locked into rocks and fossil fuels, and volcanoes and weathering slowly return it. People now burn fossil fuels and clear forests, adding carbon faster than natural sinks can take it up, so the CO₂ in the air rises and the Earth warms.
- Soil: How It Forms, Its Layers and How to Protect It – Soil is the thin, loose top layer of the land where plants grow. It is a mix of rock grains (about 45%), organic matter or humus (about 5%), water (about 25%) and air (about 25%). Soil forms very slowly when weathering breaks parent rock and living things add humus. Five factors control it: parent rock, climate, living things, relief (slope) and time. A cut through the ground shows layers called horizons: O (litter and humus), A (topsoil), B (subsoil, where washed-down minerals collect), C (broken rock) and R (bedrock). Soil texture depends on the share of sand, silt and clay. Soil feeds plants, stores and cleans water, stores carbon and is home to countless organisms, but erosion, salt and pollution can destroy it far faster than it forms.
3. 3.3 Energy resources
3.3.1 Energy supplies and the development of society · 3.3.2 Features of energy resources and their use · 3.3.3 Sustainability of current energy exploitation · 3.3.4 Strategies to secure future energy supplies
- Energy Resources: Use, Global Mix and a Sustainable Future – Societies need energy to grow food, make goods, move people and run homes. Richer countries use far more energy per person. About 80% of the world's primary energy still comes from fossil fuels (oil, coal, gas), which are non-renewable and release CO₂. Renewable sources (solar, wind, hydro, geothermal, biomass) are flows that keep returning; nuclear is non-renewable but low-carbon. Each source differs in cost, reliability, location and pollution. Energy resources are unevenly spread, so countries work for energy security by diversifying sources, trading, storing energy, saving energy and investing in new technology such as hydrogen and fuel cells.