To understand sand, it would help to know about erosion first. Try the activity Chalk It Up to Science. Most of the sand in the world comes from the erosion of large rocks into smaller and smaller pieces.

Have you ever seen sand outside? Where was it? You might have seen it on the beach, or perhaps in a desert. But sand is on the move, from the highest mountains to the bottom of the ocean. Sand can be found almost anywhere in the world.

Africa has two of the most interesting places to see sand. In northern Africa, the Sahara Desert is the largest desert in the world, and most of it is covered in sand. In southern Africa, the Namibian Sand Dunes are the talles sand dunes in the world, about 200 meters (650 feet) high.

So how many grains of sand are there in the world? You could start off by trying to guess how many grains of sand there are in a spoon of sand. Use a magnifying glass to count how many grains fit in a small section. Then, count how many of those sections fit in your spoon. Multiply the two numbers together to get an estimate.

Using this same principle, plus some additional information, mathematicians at the University of Hawaii tried to guess how many grains of sand are on the world's beaches. They came up with 7,500,000,000,000,000,000, or seven quintillion five quadrillion grains of sand.

Jim Carleton's Photos of Namibian Sand Dunes
http://www.physics.carleton.ca/~jim/sossusv/

Marblehead: Our Beaches
Where Does Sand Come From? http://www.field-guides.com/book/beaches.htm

Namibia
http://www.public.iastate.edu/%7Ekasino/namibia.html

Sahara Desert
http://edtcserver.coe.tamu.edu/courses/645/GPSp99/Integ/Chen/saha1.html

University of Hawaii
Grains of Sand on the World's Beaches http://www2.hawaii.edu/suremath/jsand.html

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