United Grade 9 Earth and Space Science
Chapters: 5
1. Space systems
Nuclear fusion in the Sun and energy to Earth · Big Bang evidence · Stellar nucleosynthesis · Orbital motion and Kepler’s laws
- Cosmology: The Expanding Universe and the Big Bang – Cosmology is the study of the whole universe: its structure, history and future. Galaxies gather in groups, clusters and filaments around huge voids. Distant galaxies are moving away from us, faster the farther they are (Hubble's law, v = H₀d), because space itself is expanding. Running the expansion backwards leads to a hot, dense beginning about 13.8 billion years ago, the Big Bang. The main evidence is redshift, the cosmic microwave background and the amounts of hydrogen and helium. Most of the universe is dark matter and dark energy.
- Kepler's Laws of Planetary Motion – Kepler gave three rules for how planets move. 1) Each planet moves on an ellipse with the Sun at one focus. 2) The line from the Sun to the planet sweeps equal areas in equal times, so the planet moves faster when it is near the Sun. 3) The square of the time for one round (T²) is proportional to the cube of the semi-major axis (a³). The second law is really conservation of angular momentum. The third law follows from Newton's law of gravitation.
2. History of Earth
Ages of crust and plate tectonics · Early Earth history from rocks and meteorites · Surface features from internal and surface processes
- Distribution of Oceans and Continents: Drift, Spreading and Plates – In 1912 Alfred Wegener said all continents were once one landmass, Pangaea, surrounded by one ocean, Panthalassa, and that they drifted apart. Matching coastlines, rocks, fossils, glacier deposits and placer gold supported him, but he could not explain the force. Mapping the ocean floor showed ridges, plains and trenches; Harry Hess then proposed sea-floor spreading: new crust forms at mid-ocean ridges and old crust sinks at trenches. This led to plate tectonics: the lithosphere is broken into rigid plates that move on the soft asthenosphere and meet at divergent, convergent and transform boundaries. The Indian plate broke away from the south, moved north, and collided with Asia to raise the Himalayas.
- Radioactivity: Alpha, Beta, Gamma and Half-Life – Some atomic nuclei are unstable. They give out radiation at random to become more stable. This is radioactive decay. Alpha (2 protons + 2 neutrons), beta (a fast electron) and gamma (a wave of energy) are the three main kinds. Half-life is the time for half of the unstable nuclei to decay.
3. Earth's systems
Feedbacks among Earth systems · Earth’s interior and mantle convection · Properties of water in Earth processes · Carbon cycle through Earth systems · Coevolution of life and Earth systems
- Earth as a System: Spheres and Energy – Earth is like one big machine with five parts: rock (geosphere), water (hydrosphere), ice (cryosphere), air (atmosphere) and life (biosphere). The Sun powers it. Sunlight comes as many kinds of rays (the electromagnetic spectrum). The Sun heats Earth unevenly, and that makes winds, breezes and ocean currents. Water, carbon, nitrogen and oxygen move round and round between the spheres in cycles. Humans now change these cycles, so we must use Earth carefully.
- Distribution of Oceans and Continents: Drift, Spreading and Plates – In 1912 Alfred Wegener said all continents were once one landmass, Pangaea, surrounded by one ocean, Panthalassa, and that they drifted apart. Matching coastlines, rocks, fossils, glacier deposits and placer gold supported him, but he could not explain the force. Mapping the ocean floor showed ridges, plains and trenches; Harry Hess then proposed sea-floor spreading: new crust forms at mid-ocean ridges and old crust sinks at trenches. This led to plate tectonics: the lithosphere is broken into rigid plates that move on the soft asthenosphere and meet at divergent, convergent and transform boundaries. The Indian plate broke away from the south, moved north, and collided with Asia to raise the Himalayas.
- Water in the Atmosphere – Air always holds some water as invisible vapour; the amount is called humidity. Absolute humidity is the actual mass of vapour in a volume of air; relative humidity is how full the air is compared with the most it could hold at that temperature. Water becomes vapour by evaporation (taking heat) and turns back to water by condensation (giving heat) when air cools to its dew point. Condensation near the ground gives dew, frost, mist and fog; higher up it gives clouds: cirrus, cumulus, stratus and nimbus. When drops or crystals grow heavy they fall as precipitation: rain, snow, sleet or hail. Rain forms in three main ways: convectional, orographic (relief) and cyclonic (frontal). Rainfall is heaviest near the equator and on windward coasts, and least in subtropical deserts, continental interiors and polar lands.
- 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.
4. Weather and climate
Energy flow and climate change drivers · Climate model forecasts
- Weather and Climate: From the Atmosphere to the Monsoon – The atmosphere is a blanket of air around the Earth: 78% nitrogen, 21% oxygen and 1% other gases. It has five layers; all weather happens in the lowest, the troposphere. Weather is the state of the air on one day: temperature, pressure, wind, humidity, clouds and rain. Climate is the average weather of 30 years or more. India has four seasons, and the monsoon winds bring most of its rain. Burning fuels adds carbon dioxide, which warms the Earth and brings more floods and heatwaves. Our carbon footprint is how much of this gas our life adds.
- 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).
5. Human sustainability
Resources, hazards and human civilization · Cost-benefit of resource extraction · Sustainability of human populations · Solutions to reduce human impact · Computational models of human impact
- Natural Resources – Natural resources are useful things we take from nature: sunlight, wind, water, soil, forests, minerals, oil, gas and coal. Renewable resources come back in a human lifetime; non-renewable ones took millions of years to form and run out when used. Resources are spread unevenly because they form only where certain geological processes happened in the past (old seas, volcanoes, mountain building). Using them brings benefits such as energy, jobs and materials, but also costs such as pollution, habitat loss and hazards, so societies weigh costs against benefits and try to use them sustainably.