Inside the Earth Lesson 41 of the geography course of Mova's primary school: 17 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 is not solid rock all the way through: it is built in layers, a bit like a peach with a thin skin, thick flesh and a hard stone in the middle. 1 The skin is the crust we live on, the flesh is the mantle of hot rock, and the stone is the core of iron and nickel, liquid outside and solid inside. 2 Think of a Scotch egg cut in half at a picnic: the breadcrumb crust is thin, the sausage meat is thick, and the yolk sits in the centre; the real crust is far thinner than the breadcrumbs compared with the whole. 3 Nobody has ever dug down to the mantle, so scientists "listen" to earthquake waves passing through the planet, which bend, speed up, slow down or stop as they cross the different layers. 4 The inside is hot because of heat left from when the Earth formed and because radioactive elements in the rock slowly break down and give off heat. 5 The Earth is built in layers: a thin rocky crust, a thick hot mantle, a liquid outer core and a solid inner core. 6 The crust is only about 5-10 km thick under the oceans and about 30-70 km thick under the continents. 7 The mantle is about 2,900 km thick and is solid rock, but over millions of years it slowly flows like very stiff putty; only small pockets of it melt into runny rock. 8 The outer core is liquid iron and nickel, and its swirling makes the Earth's magnetic field, the one a compass needle feels. 9 The inner core is a solid ball of iron and nickel about 2,400 km across (a radius of about 1,200 km), roughly as hot as the surface of the Sun, about 5,000-6,000 °C, even hotter than the liquid outer core around it. 10 The inner core stays solid despite the heat because the enormous pressure of everything above squeezes it. 11 Nobody has ever been to the mantle or the core; we know about them by studying how earthquake waves travel through the Earth. 12 Some earthquake waves (S waves) cannot pass through liquid, and the way they vanish on the far side of the Earth showed that the outer core is liquid. 13 The deepest hole ever drilled, the Kola Superdeep Borehole in Russia, reached about 12 km, not even halfway through the continental crust there. 14 The heat inside the Earth comes partly from when the planet formed and partly from radioactive elements slowly breaking down. 15 The crust and the stiff top of the mantle together form the lithosphere, the hard shell that is broken into plates. 16 The distance to the centre of the Earth is about 6,370 km, a bit more than the distance from London to New York (about 5,600 km). ← previous The game map and the real map: what EU5 simplifiesnext → Plate tectonics↑ back to Geography This page in Markdown → https://md.mova.elamur.ai/free/en/corpora/school/geography/41-inside-the-earth/