the earth

The Earth

The earth is a spherical spaceship held in orbit round the sun by the pull of gravity. The atmosphere and everything on earth is held to it by gravity. The gravitational force also crushes the earth itself so that the rocks inside are very dense.

Inside the earth there are three main layers, as shown:

The core is very hot metal, mostly iron and nickel. Most of it is liquid, but the centre is under such high pressure that is solid. The earth’s magnetic field is probably due to currents in the core. The core is hot because it is radioactive.
The mantle is mostly solid rock but some of it is slushy a mixture of solid and hot molten (liquid) rock rather like lava from a volcano. The mantle can move very slowly in giant convection currents.
The crust is a very thin solid layer like the shell on an egg.

The Earth and Sun

The earth moves round the sun in an orbit which is almost a circle. The earth is pulled into this orbit by a centripetal force. This f...