The world is planet Earth. Earth formed approximately 4.5 billion years ago and life appeared on its surface one billion years later. The world is home to millions of species and of course to every human alive. It has seven continents, five oceans and about 200 countries. It also has many great rivers like the Nile and the Amazon, huge mountain ranges like the Andes and the Himalayas, deserts like the Gobi and the Sahara and seas such as the Caribbean and the Mediterranean.