Patricia Sytnick, age 12, of Winnipeg, Manitoba, Canada, for her question:

Does the earth's weight change?

About 8,000 years ago, the earth gained about five million tons in a single day. A whopping meteorite landed in Arizona    never to return to its wanderings through interplanetary space. In 1908, another such weighty meteorite landed in Siberia. Such events are rare. But every year the earth is struck by an estimated 100 million pebble sized meteorites and fragments of meteoric dust. As they plummet down, friction with the atmosphere ignites them and we see them as so called falling stars. The crusts of sizeable meteors are scorched and the fine fragments are consumed to ashes that finally drift down on land and sea.

Scientists estimate that meteoric material adds about five million tons to the earth's weight every year. The total weight of the world is estimated to be around 6.6 sextillion tons. This is 6,600 plus 18 zeros    and the gain of a few million tons is a mere trifle. But the earth has been gaining this weight at a steady rate through billions of years.