Reading rocks, Earth's layers and moving plates. Crystal size records how fast a rock cooled; a rigid outer shell rests on slowly flowing hot rock, and currents in the mantle carry the plates. Concept tutorials with a cross-section of the Earth and simulations of cooling magma and mantle convection.
Each lesson works two ways. Students can work through the online tutorial at their own pace (it checks their answers and saves their progress in their browser), or you can teach it to the whole class from the slides, then send students into the tutorial for the Modify and Make steps.
Every lesson guide has plain-language notes, the answers to every check, a solution for every task, and slides and a worksheet for Waypoints Prepare. These guide pages are not linked from student pages, but they are not secret either: keep printed Teacher editions for answers you do not want students to find.
How igneous rocks form, and what their crystals tell us (AC9S8U04).
Igneous rocks form when molten rock cools and sets solid. Underground it is called magma; when it reaches the surface it is lava.
So crystal size is a record of cooling rate: a geologist can read where a rock formed from its crystals.
Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.
Safety and ethics: the hot solution can scald, so the teacher pours it; wash hands after handling alum. If students collect rocks or sand, check with local Traditional Owners or your school's First Nations contacts first.
Earth's layers, the plates and what drives them (AC9S8U03).
Layers: a thin solid crust (about 35 km under continents, 7 km under oceans), a thick solid mantle that flows very slowly, a liquid outer core and a solid inner core (iron and nickel). Temperature and pressure rise with depth. The lithosphere is the crust plus the rigid top of the mantle; below it the asthenosphere is solid but soft enough to flow.
Earth's outer shell, the lithosphere (the crust and the top of the mantle), is broken into large rigid pieces called tectonic plates. They move a few centimetres a year, up to about twice as fast as fingernails grow. Australia moves about 7 cm north each year.
The plates sit on the hot mantle. The mantle is solid rock, but it is so hot that over millions of years it flows very slowly, like extremely thick putty. Heat from the core warms the bottom of the mantle, and radioactive elements in the mantle rock heat it from within (about half of Earth's inner heat comes from radioactive decay); hot rock is less dense, so it rises; near the top it cools, becomes denser and sinks. This loop is a convection current, and it drags the plates along. Where currents rise, plates move apart; where they sink, plates move together.
Scientists now think two pulls also matter: old, cold plate sinking into the mantle at subduction zones drags the rest of the plate (slab pull), and plates slide away from high mid-ocean ridges (ridge push). Both are part of the same convection system.
Optional ideas if you run a practical for this unit: pick one, adapt it to your equipment, or use your own.
Safety and ethics: use warm tap water, not boiling.