--- marp: true theme: default html: true --- # What moves the plates? Year 8 Earth and space · Plate tectonics --- ## Today **We are learning to** the lithosphere is broken into rigid plates that move a few centimetres a year. Slow convection currents in the hot mantle carry them, driven by Earth's inner heat: from the core below and from radioactive elements in the mantle rock itself. - I can explain that the lithosphere is divided into plates that move. - I can describe mantle convection as the mechanism that moves the plates. - I can state that plates move a few centimetres a year. --- ## Why it matters > Australia is moving north about 7 centimetres a year, nearly twice as fast as your fingernails grow. A whole continent. What could possibly push it? --- 💬 Discussion ## Engage: predict **Earth's surface is broken into huge plates that move a few centimetres a year. What do you predict moves them?** - The pull of the Moon - Earthquakes pushing them along - Slow currents in the hot rock below them - Ocean currents and waves --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fearth-8%2Fplates%2Fstep-2&code=widget%3A+convection%0Apreset%3A+mantle%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/earth-8/plates/?full=step-2#step-2) --- ✅ Check ## What happened? * Slow currents in the hot mantle below: heated rock rises, spreads under the plates, cools and sinks, carrying the plates with it. The heat comes from the core below and from radioactive elements in the mantle rock. --- ✅ Check ## The layers **Put each description with its part of the Earth.** Groups: Lithosphere (the plates) · Mantle · Core Rigid pieces that move a few centimetres a year · Hot solid rock that flows very slowly · Heats the mantle from below · Also heated from within, by radioactive elements in its rock · Where the convection currents are · The crust and the top of the mantle * Answer: Rigid pieces that move a few centimetres a year → Lithosphere (the plates); Hot solid rock that flows very slowly → Mantle; Heats the mantle from below → Core; Also heated from within, by radioactive elements in its rock → Mantle; Where the convection currents are → Mantle; The crust and the top of the mantle → Lithosphere (the plates) --- ✅ Check ## Why rock rises **Why does hot rock above the core rise?** - Hot things always go up because heat rises - It is less dense than the cooler rock around it - The core pushes it out - It has melted into liquid magma, which floats up * Answer: It is less dense than the cooler rock around it --- ✅ Check ## Plates move apart **On the board, where did the two plates move apart?** - Above the sinking currents - Above the rising current - Where the board was coolest * Answer: Above the rising current --- ✅ Check ## How fast **Australia moves about 7 cm north each year. How many kilometres is that in a million years? (100,000 cm = 1 km)** * Answer: 70 --- ✍️ Activity ## Elaborate: the same idea in water {{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fearth-8%2Fplates%2Fstep-4&code=widget%3A+convection%0A}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/earth-8/plates/?full=step-4#step-4) --- ✅ Check ## Water and rock **What is the biggest difference between the water and the mantle?** - Mantle rock is solid and flows millions of times more slowly - Mantle rock rises when it cools - There is no heat source under the mantle * Answer: Mantle rock is solid and flows millions of times more slowly --- ✅ Check ## Three forces **Match each force to how it moves a plate.** | | | |---|---| | `Slab pull` | A. A plate slides away, downhill, from a high mid-ocean ridge | | `Ridge push` | B. Flowing mantle carries the plate above it along | | `Mantle drag` | C. Old, cold, dense plate sinks into the mantle and drags the rest of the plate behind it | * Answer: Slab pull → C. Old, cold, dense plate sinks into the mantle and drags the rest of the plate behind it; Ridge push → A. A plate slides away, downhill, from a high mid-ocean ridge; Mantle drag → B. Flowing mantle carries the plate above it along --- ✅ Check ## Which matters most? **The fastest plates (like the Pacific plate) are the ones with long edges sinking into the mantle. Which force does that suggest matters most?** - Neither: plate speed is random - Slab pull - Ridge push * Answer: Slab pull --- ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - The **lithosphere** (crust and top of the mantle) is broken into rigid **tectonic plates**, moving a few centimetres a year. - Earth's inner heat (from the **core** below, and from radioactive elements in the mantle rock) drives **convection currents** in the **mantle**: hot rock is less dense and rises, spreads, cools and sinks. - The currents carry the plates: apart above rising rock, together above sinking rock. - The mantle is solid rock that flows extremely slowly, not liquid magma. --- ✅ Check ## Exit ticket **What drives the movement of tectonic plates?** * Convection currents in the mantle: heated rock rises, spreads, cools and sinks, carrying the plates. The heat comes from the core and from radioactive elements in the mantle.