The structure of the Earth
The Earth can be compared to an onion: it is built of several layers. The top layer is the crust: it is made of cooled, solid rock and is split into large plates. The crust is not the same everywhere: under the ocean it is only about 5 km thick, while under the highest mountains it reaches 70–80 km. Below the crust lies the mantle; it is very thick (about 2,900 km) and its temperature reaches thousands of degrees. The mantle material creeps very slowly. Deepest of all is the core: the outer core is liquid metal, while the inner core is solid because of the enormous pressure and is the hottest part. Nobody has dug down to the mantle; even the deepest boreholes have only pierced part of the crust. So scientists study the inside of the Earth indirectly: they examine rock thrown out by volcanoes and measure how earthquake waves travel through the Earth. Miners also notice that a shaft gets warmer the deeper it goes — so the inside of the Earth is hot.
“Earth model”: make a model of the Earth from four colours of plasticine: a small yellow ball in the middle (inner core), wrapped in an orange layer (outer core), then a thick red layer (mantle) and a thin brown layer on top (crust). An adult cuts the model in half with a plastic knife; name the layers.