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_Is the Earth Young?_

A Response to the _Helium_ Argument

_3. The atmosphere has less than 40,000 years worth of helium,
based on just the production of helium from the decay of uranium
and thorium. There is no known means by which large amounts of
helium can escape from the atmosphere. The atmosphere appears to be
young. a) Melvin A. Cook, Prehistory and Earth Models (London: Max
Parrish, 1966), pp. 10-14. _

Cook, as it turns out, was wrong. There are two basic mechanisms for
getting helium out of the earth's atmosphere, thermal escape (which
Cook must have known about) and ionic escape (which Cook either did
not know about or underestimated).

Thermal escape is the standard method. Helium being the lightest thing
around save hydrogen, it will tend to predominate at the highest
levels of the [1]earths atmosphere, the thermosphere. Some of the
helium atoms will gain enough energy, either by collision, of through
absorption of solar energy, to escape from earth altogether. If Cook
made use of only the thermal escape mechanism, he would have
underestimated the rate of helium escape, and derived an inconsistency
between the relatively high rate of production, low rate of escape,
and amount present, if one assumes an old earth.

However, it has been shown that helium ionizes and can then escape
preferentially along the lines of the earth's magnetic field, where
the field is concentrated near the poles. By adding up all of the
known escape mechanisms and production mechanisms, it now appears that
helium is in equilibrium in the earth's atmosphere. The present
abundance is not a problem for the old earth.

Larry Vardiman made the same argument in [2]I.C.R. Impact #143, May
1985. He mentions ionic escape, but assumes it is insufficient. But
the papers I reference below came out some time later, and show that
the ionic outflow mechanism is quite sufficient to solve the problem.

_References_
_________________________________________________________________

_Helium Escape from the Terrestrial Atmosphere - The Ion Outflow
Mechanism_
O. Liesvendsen & M.H. Rees
[3]Journal of Geophysical Research (Space Physics) v101(A2):
pp2435-2443 (1996 Feb 1)

_We have computed global He+ escape fluxes for a range and a variety
of diurnal, seasonal, universal time, and solar activity geophysical
conditions. We average over the short-term variables and compute the
globally averaged escape flux for a range of cutoff latitudes, which
separate regions of open and closed field lines, during one solar
cycle. The global escape flux averaged over a solar cycle was
computed, and we find that a cutoff latitude of about 60 degrees or
lower is sufficient to balance the outgassing from the Earth's crust._
_________________________________________________________________

_Helium Escape from the Earth's Atmosphere - The Charge-Exchange
Mechanism Revisited_
O. Liesvendsen, M.H. Rees & K. Stamnes

[4]Planetary and Space Science v40(12): pp1639-1662 (1992 Dec)

_We have studied the escape of neutral helium from the terrestrial
atmosphere through exothermic charge exchange reactions between He+
ions and the major atmospheric constituents N2, O2 and 0. Elastic
collisions with the neutral background particles were treated
quantitatively using a recently developed kinetic theory approach. An
interhemispheric plasma transport model was employed to provide a
global distribution of He+ ions as a function of altitude, latitude
and local solar time and for different levels of solar ionization.
Combining these ion densities with neutral densities from an MSIS
model and best estimates for the reaction rate coefficients of the
charge exchange reactions, we computed the global distribution of the
neutral He escape flux. The escape rates show large diurnal and
latitudinal variations, while the global average does not vary by more
than a factor of three over a solar cycle. We find that this escape
mechanism is potentially important for the overall balance of helium
in the Earth's atmosphere. However, more accurate values for the
reaction rate coefficients of the charge exchange reactions are
required to make a definitive assessment of its importance._
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References

1. http://liftoff.msfc.nasa.gov/academy/space/atmosphere.html
2. http://www.icr.org/pubs/imp/imp-143.htm
3. http://plasma2.ssl.berkeley.edu/jgr/
4. http://www.elsevier.com/inca/publications/store/2/0/0/
5. file://localhost/www/sat/files/tim_thompson/young-earth.html#3