Kim Williams, age g, of Cape Girardeau, Mo., for her question:

Do we know the weight of the earth?

Experts can tell us the weight of our world with everything in it. Perhaps the figure is not perfectly accurate to the last ounce, but it is accurate enough to satisfy our curiosity. The Weight of the earth is roughly 6 sextillion, 570 quintillion tons. Now you have to learn the names of some of the big big numbers.

In the meantime, you can take a pencil and write the weight of the earth in figures. Write 6,570 and follow it with 18 zeros. When you have finished, count back from the last zero and put a comma after every three zeros. That figure is the estimated weight of the earth with all its mountains and seas, its air and its oceans.