Plate tectonics Lesson 42 of the geography course of Mova's primary school: 16 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: the lesson at school .
0 The Earth's hard outer shell, the lithosphere, is cracked into giant pieces called plates, which fit together like a jigsaw that has been dropped on the floor. 1 The plates are always moving, very slowly, about as fast as your fingernails grow, carried on the slowly flowing mantle below. 2 The strongest push comes from the edges: old, cold ocean plate is heavy, sinks into the mantle and drags the rest of the plate behind it, like a tablecloth sliding off a table once enough of it hangs over the edge. 3 What happens at a plate's edge depends on how the plates meet: pulling apart makes new sea floor, one diving under another makes trenches and volcanoes, two continents crashing makes mountains, and plates grinding sideways make earthquakes. 4 For fifty years after Alfred Wegener said the continents move, most scientists laughed; then striped magnetic rocks on the sea floor proved him right, and today GPS measures the movement every day. 5 The lithosphere is broken into about 15 large plates and many smaller ones that fit together like a cracked jigsaw. 6 Plates move about 2-10 cm a year, roughly as fast as your fingernails grow. 7 The biggest force moving plates is slab pull: old, cold ocean plate is heavy and sinks into the mantle, dragging the rest behind it. 8 Where plates move apart, magma rises to fill the gap and makes new crust, as along the Mid-Atlantic Ridge. 9 Where an ocean plate meets another plate, the denser one dives down in a subduction zone, making a deep trench and a line of volcanoes. 10 When two continents collide, neither sinks, because continental crust is too light, so the crust crumples upwards into huge mountains, such as the Himalayas, where India is still pushing into Asia. 11 Where plates slide past each other sideways, crust is neither made nor destroyed, but strong earthquakes happen, as along the San Andreas Fault in California. 12 About three-quarters of the world's active volcanoes and most big earthquakes lie around the Pacific, in the Ring of Fire. 13 Alfred Wegener proposed in 1912 that continents drift, but most scientists rejected the idea until the 1960s, partly because he could not explain what moved them. 14 The sea floor has stripes of rock magnetised in alternate directions, matching on both sides of ocean ridges, because the magnetic field flips now and then while new crust forms at the ridge. 15 Today satellites measure plate movement directly: GPS stations show Europe and North America moving apart about 2.5 cm a year. ← previous Inside the Earthnext → Moving continents: from Pangaea to today↑ back to Geography This page in Markdown → https://md.mova.elamur.ai/free/en/corpora/school/geography/42-plate-tectonics/