--- title: "Quick check: plate boundaries and evidence" subtitle: "Year 8 Earth and space · Plate tectonics · Lesson 4" --- # Quick check: plate boundaries and evidence **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Earthquakes, volcanoes, mountains and trenches all happen at the edges of plates. What happens at each kind of edge? :::teacher-note **In one sentence:** A self-test on divergent, convergent and transform boundaries and the evidence for plate tectonics (AC9S8U03, nodes 3 to 6, taught in class; node 6 a hinge). **Students should be able to say:** I can say what forms at each kind of plate boundary. I can explain why earthquakes happen at transform boundaries. I can give three lines of evidence for plate tectonics. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Moving apart :::keep-together ### What forms **Two oceanic plates move apart. What forms at the gap?** ☐ A fold mountain range ☐ An earthquake zone only, with no new rock ☐ A deep trench ☐ A mid-ocean ridge, as magma rises and cools into new crust ::: :::teacher-note **Answer:** A mid-ocean ridge, as magma rises and cools into new crust Tension lets magma rise into the gap, where it cools into new oceanic crust. Over time this builds a ridge and spreads the seafloor. ::: :::keep-together ### Age of the seafloor **You collect rock from the seafloor at the ridge and from far away on either side. Where is the rock youngest?** ☐ At the ridge, getting older with distance ☐ Far from the ridge, getting younger towards the ridge ☐ The same age everywhere ☐ Youngest on one side only ::: :::teacher-note **Answer:** At the ridge, getting older with distance New crust forms at the ridge and moves away, so the oldest crust is furthest from it. ::: ## Colliding :::keep-together ### Ocean meets continent **An oceanic plate meets a continental plate. What happens?** ☐ The plates slide sideways past each other ☐ The denser oceanic plate sinks beneath the continent (subduction), forming a trench and a line of volcanoes ☐ Both plates sink equally ☐ Both plates stop moving ::: :::teacher-note **Answer:** The denser oceanic plate sinks beneath the continent (subduction), forming a trench and a line of volcanoes Oceanic crust is denser, so it sinks. A deep trench forms at the bend, and melting above the sinking plate feeds a volcanic arc. ::: :::keep-together ### Continent meets continent **Why does a collision between two continents make mountains rather than subduction?** ☐ Both are light, buoyant crust, so neither sinks easily and the rock crumples upwards ☐ The plates stop moving when they meet ☐ One continent always slides under the other, as ocean crust does ☐ Continental crust is denser than the mantle, so it sinks ::: :::teacher-note **Answer:** Both are light, buoyant crust, so neither sinks easily and the rock crumples upwards Continental crust is too light to sink far. The collision squeezes and folds the rock upwards, as in the Himalayas. ::: ## Sliding past :::keep-together ### Why earthquakes? **Two plates slide past each other along a transform boundary. Why do earthquakes happen there?** ☐ Magma pushes the plates apart ☐ The plates melt ☐ The plates stop moving ☐ The plates stick, stress builds, and the rock suddenly slips and releases it ::: :::teacher-note **Answer:** The plates stick, stress builds, and the rock suddenly slips and releases it Friction locks the plates for a while. When the stress becomes too great, the rock slips and the energy is released as an earthquake. ::: :::keep-together ### Volcanoes? **Do transform boundaries have volcanoes?** ☐ Yes, because of friction ☐ Usually not, because plates are neither pulling apart nor sinking, so magma does not form ☐ Yes, many large ones ☐ Yes, but only in the ocean ::: :::teacher-note **Answer:** Usually not, because plates are neither pulling apart nor sinking, so magma does not form Volcanoes need magma. Sliding past does not make a gap for magma to rise or push a plate down into the mantle to melt. ::: :::keep-together ### Which boundary? **Which kind of boundary is it?** Groups: Divergent, Convergent, Transform - Mid-ocean ridge: {{field-15}} - Ocean trench: {{field-15}} - San Andreas Fault in California: {{field-15}} - Himalayas: {{field-15}} - East African Rift: {{field-15}} ::: :::teacher-note **Answer:** Mid-ocean ridge → Divergent; Ocean trench → Convergent; San Andreas Fault in California → Transform; Himalayas → Convergent; East African Rift → Divergent ::: ## Evidence :::keep-together ### Evidence or not? **Is it evidence that the plates have moved?** Groups: Evidence, Not evidence - The coastlines of South America and Africa fit together: {{field-15}} - The same fossils on continents now separated by ocean: {{field-15}} - The seafloor is youngest at the mid-ocean ridges: {{field-15}} - Earthquakes and volcanoes line up along plate edges: {{field-15}} - The Moon has craters: {{field-15}} ::: :::teacher-note **Answer:** The coastlines of South America and Africa fit together → Evidence; The same fossils on continents now separated by ocean → Evidence; The seafloor is youngest at the mid-ocean ridges → Evidence; Earthquakes and volcanoes line up along plate edges → Evidence; The Moon has craters → Not evidence ::: :::keep-together ### The strongest evidence **Which evidence most strongly shows the seafloor is spreading from ridges?** ☐ Earthquakes along the ridges ☐ The pattern of rock ages: young at the ridge, older with distance, the same on both sides ☐ The size of the oceans ☐ Coastlines that look alike ::: :::teacher-note **Answer:** The pattern of rock ages: young at the ridge, older with distance, the same on both sides The matching age pattern on both sides is what spreading predicts, and is hard to explain any other way. ::: :::keep-together ### What each shows **Match each piece of evidence to what it shows.** A. The continents were once joined B. Where plates meet and move against each other C. The same plants and animals once lived on connected land D. New crust forms at the ridges and spreads outwards {{columns 60% 40%}} {{rows 1}} | Part | Letter | |---|---| | `Coastlines of South America and Africa fit` | | | `The same fossils on continents now far apart` | | | `Seafloor youngest at the ridges` | | | `Earthquakes and volcanoes in lines` | | ::: :::teacher-note **Answer:** Coastlines of South America and Africa fit → A. The continents were once joined; The same fossils on continents now far apart → C. The same plants and animals once lived on connected land; Seafloor youngest at the ridges → D. New crust forms at the ridges and spreads outwards; Earthquakes and volcanoes in lines → B. Where plates meet and move against each other ::: ## Exit ticket :::keep-together **Name the three kinds of plate boundary and one feature of each.** {{lines-3}} ::: :::teacher-note **Answer:** Divergent: mid-ocean ridge. Convergent: trench, volcanic arc or fold mountains. Transform: earthquakes along a fault. :::