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 Subject: Gaining or Loosing Category: Science > Astronomy Asked by: haluk-ga List Price: \$5.00 Posted: 05 Nov 2002 01:59 PST Expires: 05 Dec 2002 01:59 PST Question ID: 99133
 ```Earth is getting a lot of space dust and meteors from the space. On the other hand our athmosphere is loosing some gases. Which one is greather? Is Earth gaining or loosing?```
 Subject: Re: Gaining or Loosing Answered By: willie-ga on 05 Nov 2002 05:25 PST Rated:
 ```Hello, and thanks for the question. According to Jeff Brown at Washington State University, several hundred tons of meteorites enter the Earth's atmosphere every day. The total amount per year can range from 10 million to 1 billion kilograms. A lot of this is just dust or micrometeorites, but it adds up. For example, let's say an average of 500 million kilograms a year has landed on Earth over the past 10,000 years. That's 5 trillion kilograms. Or 5 billion metric tons. That might seem like a lot, but the total mass of the Earth is over 5 x 1021 metric tons! (That's a 5 with 21 zeroes.) The Earth also loses mass in several ways. All the time, we're losing light elements, mostly hydrogen, from the atmosphere. In a study "PLANETARY SCIENCE:ON THE SOLAR WIND AND ATMOSPHERE EROSION" (http://scienceweek.com/st16.htm ) The author points out that "....at present the Earth loses matter at a rate of 1 to 3 kilograms per second, the rate and composition varying with solar cycle (sunspot cycle). Recent measurements (K. Seki et al, Science 291:1939 2001) suggest the rate is lower than this, but even with a net loss of 3 kilograms per second, it would take 50 billion years to deplete the Earth's atmosphere and at least another 15 trillion years to evacuate the oceans. For comparison, the total lifetime of the Sun is only approximately 10 billion years." Assuming the worst case from this study, say we lose 3kg/second. That works out at: 3*60secs*60mins*24hours*365.25days or 94,672,800 Kg/year So to answer your question, over long periods of time we gain more from "space dust" and asteroids than we lose from the escape of gases, but in some years it may be a net loss. But gas escape is not the only way we lose mass. Another way the Earth loses mass is through radioactive decay. The Earth's interior is peppered with radioactive elements such as uranium, thorium and potassium 40. These radioactive elements are mixed in with other rock. Granite, for example, can contain as much as four grams per ton of uranium and 13 grams per ton of thorium. As these radioactive elements decay, they give off heat and in the process of releasing this energy, the elements also lose mass. Gary Collins, who is a physicist at WSU, says …"it should be possible to figure out approximately how much mass is lost, but it would be a difficult calculation" Taken from: "Ask Dr Universe: The Big Questions" at (http://www.wsu.edu/DrUniverse/earth4.html ) And "space dust" and meteorites are not the only ways we gain mass. For one, Earth gains a tiny amount of mass from the "solar wind," the stream of charged particles from the Sun's corona. This varies wildly, as you’ll find from the NASA site on the solar wind here: "The Solar Wind" (http://science.msfc.nasa.gov/ssl/pad/solar/sun_wind.htm ) Hope that answers your question, but if you need clarification, just ask. willie-ga Google search used earth mass gain loss``` Request for Answer Clarification by haluk-ga on 06 Nov 2002 02:38 PST ```Thank for your answer, Would you Clearfy: Over long period of time, if we gain more mass from space, why moon is (slowly) escaping from us?``` Clarification of Answer by willie-ga on 06 Nov 2002 03:32 PST ```Hello again The net amount of mass the earth is gaining, at the highest estimate 5 x 10 to the power 8 kg/yr, is very small compared to the total mass of the earth at 5 x 10 to the power 24 kg i.e. the added mass, at best, is 1/10000000000000000 of the total mass of the earth....not something to cause a big effect. The moon is moving away due to a combination of factors, mainly due to "tidal friction". There's a very nice run down here: Ask an Astronomer: Is the Moon moving away from the Earth? When was this discovered? ( http://curious.astro.cornell.edu/question.php?number=124 ) willie-ga```

 ```First of all, the amount of space dust and meteors we are gaining cannot be described as very much, from what i understand (i may be wrong however). knowing of only one gas that reaches escape velocity (there probably are others, i just dont know) being helium, i would suspect that overall we are losing. The only way we get helium is from the decay of uranium and other radioactive elements. This helium eventually leaves the atmosphere altogether. Since there is a significant amount of helium used in the world, this leads me to believe overall we are losing, however, I will admit I cannot justify my claim. Thus I post it as a comment.```
 ```There doesn't seem to be any consistency over how much material lands on Earth each day - willie-ga has quoted several hundred tons, I've seen figures up to 3000 tons/day from dust alone. Since 1986 Louis A Frank has been pushing the theory that the Earth is being bombarded by mini ice comets. If his figures are to be believed, we're gaining almost 1 million tons/day! Ian G.```
 ```I agree with willey: we are gaining mass. In the upper atmosphere cosmic rays decompose water vapor and most of the free hydrogen that doesn't recombine with oxygen escapes eventually. We also loose a ton? of helium and negligible amounts of other stuff daily. Several times per billion years, a 100 trllion ton asteroid (or heavier) hits the surface. Perhaps 1000 trillion tons of debris is thrown into space, but most of it returns in hours and significantly more over the next century. I don't think we are sure weather these really big ones result in a net gain or loss, but clearly the much more numerious midsise asteroid and comet hits increase Earth's total mass just as the tiny ones increase Earth's mass. Neil```
 ```All gases should be escaping (VERY slowly). The average velocity does depend on the mass of the molecule (or atom, in the case of helium), but that's just an average. The velocities are distributed according to the Maxwell-Boltzmann distribution function, I believe, so there are some molecules moving faster than escape velocity, even if they're heavy. Once they escape, later collisions redistribute the velocity and keep refreshing the "fast tail" of the curve.```