| MadSci Network: Earth Sciences |
Have you ever seen a shooting star? A shooting star, or meteor, is a small piece of debris (sand or rock) burning up in the upper parts of the Earth's atmosphere. Each one is tiny (they're usually as large as grains of sand), but they add up to a substantial amount of mass.
Let's do a simple calculation. If you go outside and count meteors on a clear night, you might see about 1 per minute. Of course, you only see meteors which enter the atmosphere near where you're standing: if we assume you can see a patch of atmosphere 100 km across, then the total number of meteors hitting the whole earth is (very roughly)
area of earth
meteors seen per second * ------------------- = 40,000 meteors/minute
area of sky you see
Each one weighs, perhaps, .005 grams, so we multiply mass per meteor by
meteors per minute to get mass per second: 200 grams per minute. Multiply
this by the number of minutes in a year to get 105,000 kilograms per year.
This is very close to the number given by the trivia question.
(I admit, I played with my guess of the mass per meteor slightly to get a closer answer.)
This is only a rough guess: there are many, many more microscopic particles which hit the Earth, but they don't weigh very much. There are a few very big rocks which hit the earth, ranging from pebble-sized to city-sized, but they're very rare, and so don't contribute much to the average.
More information about meteors and meteorites can be found within the Nine Planets website.
Try the links in the MadSci Library for more information on Earth Sciences.