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?

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

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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?

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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.