--- marp: true theme: default html: true --- # Quick check: plate boundaries and evidence Year 8 Earth and space · Plate tectonics --- ## Today **We are learning to** a few quick questions on what happens where plates move apart, collide and slide past each other, and the evidence that plates move. Taught in class; use this to check yourself. - 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. --- ## Why it matters > Earthquakes, volcanoes, mountains and trenches all happen at the edges of plates. What happens at each kind of edge? --- ✅ Check ## 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 * Answer: A mid-ocean ridge, as magma rises and cools into new crust --- ✅ Check ## 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 * Answer: At the ridge, getting older with distance --- ✅ Check ## 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 * Answer: The denser oceanic plate sinks beneath the continent (subduction), forming a trench and a line of volcanoes --- ✅ Check ## 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 * Answer: Both are light, buoyant crust, so neither sinks easily and the rock crumples upwards --- ✅ Check ## 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 * Answer: The plates stick, stress builds, and the rock suddenly slips and releases it --- ✅ Check ## 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 * Answer: Usually not, because plates are neither pulling apart nor sinking, so magma does not form --- ✅ Check ## Which boundary? **Which kind of boundary is it?** Groups: Divergent · Convergent · Transform Mid-ocean ridge · Ocean trench · San Andreas Fault in California · Himalayas · East African Rift * Answer: Mid-ocean ridge → Divergent; Ocean trench → Convergent; San Andreas Fault in California → Transform; Himalayas → Convergent; East African Rift → Divergent --- ✅ Check ## Evidence or not? **Is it evidence that the plates have moved?** Groups: Evidence · Not evidence The coastlines of South America and Africa fit together · The same fossils on continents now separated by ocean · The seafloor is youngest at the mid-ocean ridges · Earthquakes and volcanoes line up along plate edges · The Moon has craters * 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 --- ✅ Check ## 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 * Answer: The pattern of rock ages: young at the ridge, older with distance, the same on both sides --- ✅ Check ## What each shows **Match each piece of evidence to what it shows.** | | | |---|---| | `Coastlines of South America and Africa fit` | A. The continents were once joined | | `The same fossils on continents now far apart` | B. Where plates meet and move against each other | | `Seafloor youngest at the ridges` | C. The same plants and animals once lived on connected land | | `Earthquakes and volcanoes in lines` | D. New crust forms at the ridges and spreads outwards | * 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 --- ✅ Check ## Exit ticket **Name the three kinds of plate boundary and one feature of each.** * Divergent: mid-ocean ridge. Convergent: trench, volcanic arc or fold mountains. Transform: earthquakes along a fault.