Seven quintillion, five hundred quadrillion grains of sand on planet Earth - 6

You can count numbers all around you, from the eight legs on a spider to the one nose on your face. But can you count the stars in the sky or the fish in the Amazon? Find out all about PLANET EARTH in THE BIG COUNTDOWN, including types of rock and how they are formed, the longest river and smallest mountain, earthquakes and volcanoes, the water cycle and Earth's atmosphere and how we can really count the grains on sand on our planet.

The Big Countdown looks at popular topics and investigates the great many numbers that make them fascinating. From the mind-bogglingly large to smallest and most precious, this series helps us understand that it's not just our days that are numbered.