Paul Davis, age 8, of Sarasota, Fla., For his question:

How many tons does the earth weigh?

No one., of course, has put our round earth on a scale to weigh it ton by ton. But experts have used other ways to figure out the weight of the world. They tell us that the earth's weight is roughly 6 sextillion, 550 quintillion tons.

A sextillion is written as figure i followed by 21 zeros: A quintillion is 1 followed by 18 Zeros. So, if you wish to dot down the weight of the world, you will write 5,550 and then add 18 zeros. This is roughly the weight of the entire earth with everything in it.