Most scientists maintain that the Earth, the sun and the other planets of the Solar System were formed from a frozen dust cloud about 100,000 million years ago. One speck of dust attracted another in a gigantic disc was the sun. In the rings the particles formed into fireballs of gas and molten substances, which slowly began to cool down and to condense. Condensation is the change of steam into water. Then finally, the Earth reached a stable form. After this there was a long history about which it is difficult to write with precision as it goes back 5000 million years! This seems to be the most probable explanation.

The Earth is surrounded by an atmosphere of oxygen, nitrogen and other gases and 70% of the surface is covered by water. Around the centre of the Earth, there is and imaginary line (called the equator) which divides the northern hemisphere from the southern hemisphere. The equator can be measured. The circumference of the earth is 40,000 kilometres (248,000 miles). Another imaginary line separates east and west; the Greenwich meridian.