Up, Up, and Away! The Helium Escape Problem

Larry Vardiman, Ph.D.
IMPACT
No. 143, May 1985

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.

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 Vardiman[4] 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 atmosphere.[3]

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 MacDonaid [3] and Walker[2]).

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^oK or more, the escape rate could possibly explain the loss of ⁴He. However, the temperature is normally found to be less than 1500^o, 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] Cook[9] 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.

2. Walker, J.C.G., Evolution of the Atmosphere, Macmillan, 1977, 318 pp. Return to Text (first occurance)

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. Return to Text (first occurance)

4. Vardiman, L., "The sky has fallen," ICR Impact No. 128, 1983. Return to Text (first occurance)

5. Jeans, J.H., The Dynamical Theory of Gases, Cambridge U. Press, 1916, (4th Ed, 1925). Return to Text

6. Cook, M.A., "Where is the earth's helium?," Nature, 179:213 (1957). Return to Text

7. Chamberlain, J.W., Theory of Planetary Atmospheres, Academic Press, 1978, 330 pp. Return to Text (first occurance)

8. Lingenfelter, R.E., "Production of C-14 by Cosmic Ray Neutrons," Rev. of Geophys., 1, 1963, p. 51. Return to Text

9. Cook, M.E., "Do Radiological Clocks Need Repair?," Creation Research Soc. Quart., Vol. 5, 1968, p. 70. Return to Text

10. Whitelaw, R.L., "Radiocarbon Confirms Biblical Creation," Creation Research Soc. Quart., Vol. 5, 1968, p. 80. Return to Text