Up, Up, and Away! The Helium Escape Problem
by Larry Vardiman, Ph.D.
Introduction
The standard evolutionary/uniformitarian explanation
for the origin of the earth's atmosphere is by outgassing of
volatile compounds from the solid earth,1 and its
modification by escape of gases and biological processes.2
Supposedly, these processes occurred over a period of 4.5 billion
years. Many problems have been encountered, however, when attempting
to reconcile the composition and processes in today's atmosphere
with basic tenets of this model. For example, the composition
of no single planetary atmosphere in the solar system matches
the assumed primordial material which supposedly made up the
original nebula, even after complex heating, recombination,
outgassing, and escape scenarios are considered. The controversy
continues as to whether the earth originally had a reducing
or oxidizing atmosphere. It is not certain how carbon dioxide
maintains its equilibrium or why it has been increasing in recent
years, nor is it clear why methane is so plentiful on the earth.
One of the most intriguing problems with the evolutionary
model has been the attempt to explain why there isn't more helium
in today's atmosphere, if the earth has existed for 4.5 billion
years. This article will explore this problem and suggest an
alternative to the evolutionary model.
Sources of Helium
The earth's atmosphere is predominantly nitrogen
(78%) and oxygen (21%). It also contains many other minor constituents.
Table I shows a few of these taken from Walker.3
The evolutionary/uniformitarian model of the origin
of the atmosphere assumes that there were no primordial gases
but that they were all outgassed from the solid earth. One of
the sources for helium in today's atmosphere is generally agreed
to be processes in the crust. The radioactive decay of uranium
and thorium in the earth's crust produces 4He, one
of the isotopes of helium, which seeps to the surface and subsequently
mixes through the atmosphere. The flux of helium by this process
is estimated to be about 2x106 atoms/cm2-sec.3
This is an estimated rate because the exact composition of the
crust and mantle of the earth isn't known and, therefore, the
exact rate of decay of uranium and thorium is not known. Estimates
are based on measured and calculated rates of heat flow and
compositional models of the earth. Heat flow from the earth
is assumed to be caused by the initial heat of formation of
the earth and radioactive decay of uranium, thorium, and potassium.
Table 1
Composition of the Atmosphere |
| Constituent |
Chemical
Formula |
Molecular
Weight |
Percent by
Volume in
Dry Air |
Total Mass
(gm) |
| Nitrogen |
N2 |
28.013 |
78.084 |
3.866 x 1021 |
| Oxygen |
O2 |
31.999 |
20.948 |
1. 185x 1021 |
| Argon |
Ar |
39.948 |
.934 |
6.59xl019 |
| Water Vapor |
H2O |
18.015 |
Variable |
1.700xl019 |
| Carbon Dioxide |
C02 |
44.010 |
.0315 |
2.450xl018 |
| Neon |
Ne |
20.183 |
1.818x10-3 |
6.48xl016 |
| Helium |
He |
4.003 |
5.24xl0-4 |
3.71xl015 |
| Krypton |
Kr |
83.80 |
1.14xl0-4 |
1.69xl016 |
The amount of argon in the atmosphere is assumed
to be fully retained in the atmosphere after radioactive decay
of potassium, and permits maximum estimates of helium flux to
be made. Unfortunately, the assumption of long ages of the earth
underlies the estimates of heat flow and the accumulation of
argon in the atmosphere as well. This assumption likely affects
the calculation of helium accumulation. Direct measurements
of helium currently being made may help to improve these estimates.
There are two possible sources of another isotope
of helium, 3He, in the atmosphere. It is produced
by collisions of cosmic-ray neutrons with nitrogen leading to
the formation of tritium which then decays to 3He.
Tritium and 3He are also injected directly into the
atmosphere by the solar wind. Today's observed concentration
of 3He may have been strongly affected if the earth
were surrounded by a water vapor canopy until about 4000 years
ago, as suggested by Vardiman4 and others. The concentration
of 3He would have been much greater if a vapor canopy
existed, resulting in a high residual concentration today.
The abundance of neon in the atmosphere helps
set an upper limit to the gases which may have been accreted
from the sun. Neon, like argon, is too massive to have escaped
from the earth's atmosphere. Comparing the neon and 3He
flux from the sun, about 10 3He atoms/cm2-sec
are estimated to be injected into the atmosphere3
Using these estimated fluxes of helium, the present
abundance of 4He would accumulate in 1.8 million
years. Only 370 thousand years would be required to supply the
atmosphere with its present content of 3He. Even
in the case of 4He this is still 3,000 times too
small. The helium must be escaping from the atmosphere in some
way for the evolutionary model to be true. Otherwise, there
would be a great deal more helium today.
Thermal Escape of Helium
The main process which has been considered to
explain the excessive loss of helium by long-age theorists is
thermal escape. This is the process whereby light gas molecules
or atoms can escape from the gravitational attraction of a planet,
if they exceed the escape velocity. The theory for thermal escape
was first developed by Jeans.5 A significant amount
of effort has gone into applying this theory to the escape of
terrestrial helium over the past 25 years (see MacDonaid3
and Walker2).
The average rate of thermal escape of 4He
has been estimated to be about 6xl04 atoms/cm2-sec.
This is considerably less than the rate of influx of 2xl06
atoms/cm2-sec. The present abundance of 4He
in the atmosphere would still accumulate in about two million
years. The rate of thermal escape of 3He has been
estimated to be about 4 atoms/ CM2-sec, also much
less than its estimated influx.
The rate of escape of helium has been found to
be dependent on its loss rate high in the atmosphere rather
than on its upward diffusion. The main variable which affects
the loss of helium is the temperature at the base of the exosphere,
the region of the atmosphere in which collisions among gas molecules
or atoms are negligible. If the temperature were about 2000°K
or more, the escape rate could possibly explain the loss of
4He. However, the temperature is normally found to
be less than 1500° , which causes a much lower loss rate.
If the temperature at the base of the exosphere were raised
sufficiently high to explain the loss of 4He, the
loss of 3He would still not match its influx. In
fact, it has been shown that no temperature can be maintained
at which both 3He and 4He fluxes are in
equilibrium. After many years of research on the subject it
is now conceded that thermal escape alone cannot explain the
loss of helium in the earth's atmosphere. 2,3,6,7
Non-thermal Escape of Helium
If one is convinced that the age of the earth
is about 4.5 billion years old and the present amount of helium
in the atmosphere would accumulate in about 2 million years,
then there must be some other loss process in addition to thermal
escape. A number of suggestions have been made. Three of the
more popular suggestions are 1) the polar wind, 2) solar wind
sweeping, and hot ion exchange.
The polar wind is a magnetohydrodynamic expansion
into space of the ionospheric plasma at high altitudes near
the poles where the geomagnetic field is stretched far "downstream"
by the solar wind. The ions are drawn out through open magnetic
field lines by the electric field of charge separation. At high
altitudes the positive ions are sufficiently accelerated by
the electric field that they escape rather than settle into
diffusive equilibrium. The process appears to be relatively
effective for removing hydrogen from a planet, but has not been
adequately demonstrated to do the same for helium. Solar wind
sweeping is a process where the solar wind plasma sweeps up
ions as it blows by an unmagnetized planet. This is likely to
be important on Venus and Mars which have weak magnetic fields,
but not on Earth. Hot ion exchange is a process whereby an energetic
ion transfers its kinetic energy to a neutral helium ion which
can then escape. Hot ion exchange is considered to be the best
candidate for explaining terrestrial helium escape, although
the transfer rate seems too low. None of the rates of these
proposed processes have been accurately quantified nor have
adequate observations even begun to confirm or deny them. Chamberlain
states that the helium escape problem "will not go away
and it is unsolved."7
A Young Earth Model
An obvious alternative to the evolutionary model,
but one which runs counter to the basic assumption of the evolutionary/uniformitarian
model, is that the earth's atmosphere is relatively young (less
than 10,000 years). The helium we observe in the atmosphere
is primordial with possible minor increases due to short-term
decay of radioactive uranium and thorium in the earth's crust
and some unknown consequences of the collapse of a vapor canopy
during the flood.4
If the rates of influx and outflux of helium to
the earth's atmosphere are not in equilibrium, then it should
be possible to calculate the time when events like the flood
of Noah may have impacted the helium concentration. The crude
calculations in this article have already shown relatively short
periods for the accumulation of helium. Such studies have already
been done for radioactive carbon by Lingenfelter,8
Cook9 and Whitelaw.10
Conclusion
The study of the influx and outflux processes
of gases like hydrogen, helium, argon, neon, and krypton may
lead to better estimates of the age of the earth's atmosphere.
Evolutionary/uniformitarian models of the earth's atmosphere
have run into formidable obstacles in explaining these processes.
We believe the source for these problems is the assumption that
the earth's atmosphere is billions of years old.
Research in light of processes in a young atmosphere
whose processes may have been significantly modified by a recent
worldwide flood should lead to resolution of the helium problem.
REFERENCES
1. Rubey, W.W.,"Geologic history
of seawater," Bull. Geol. Soc. Am.,62,1951,pp.
1111-1147.
2. Walker, J.C.G., Evolution of the Atmosphere,
Macmillan, 1977, 318 pp.
3. Mac Donald, G.J. F., "The escape of helium
from the earth's atmosphere, "The Origin and Evolution
of Atmospheres and Oceans, Ed. by P.J. Brancazio and A.
G.W. Cameron, 1964, pp. 127-182.
4. Vardiman, L., "The sky has fallen,"
ICR Impact No. 128, 1983.
5. Jeans, J.H., The Dynamical Theory of Gases,
Cambridge U. Press, 1916, (4th Ed, 1925).
6. Cook, M.A., "Where is the earth's helium?,"
Nature, 179:213 (1957).
7. Chamberlain, J.W., Theory of Planetary Atmospheres,
Academic Press, 1978, 330 pp.
8. Lingenfelter, R.E., "Production of C-14
by Cosmic Ray Neutrons," Rev. of Geophys., 1,
1963, p. 51.
9. Cook, M.E., "Do Radiological Clocks Need
Repair?," Creation Research Soc. Quart., Vol.
5, 1968, p. 70.
10. Whitelaw, R.L., "Radiocarbon Confirms Biblical Creation,"
Creation Research Soc. Quart., Vol. 5, 1968, p. 80.
This article was originally published May, 1985. "Up, Up, and Away! The Helium Escape Problem", Institute for Creation Research, http://www.icr.org/article/247/ (accessed October 06, 2008).
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