Posted by jlwile on July 5, 2009
So far, I have discussed how the earth’s magnetic field, dendrochronology, and the amount of sodium in the oceans all indicate a very young earth. The fourth on my “top five” list is the amount of helium in earth’s atmosphere.
We all know what helium is. It is a lighter-than-air gas. When we fill a balloon with helium, the balloon floats in air. What you might not know is that there is actually some helium in the earth’s atmosphere. There are roughly 5 atoms of helium for every million atoms (or molecules) in the atmosphere. Obviously, that’s not much helium, and that’s not what you would expect if the earth is ancient.
There is essentially only one way that helium can be produced on earth: through radioactive decay. Some naturally-occurring radioactive substances in earth’s crust produce helium as a part of their radioactive decay process. The helium then slowly diffuses out of the rocks of the earth and into the atmosphere. Believe it or not, it is reasonably easy to estimate how much helium is being produced by this process. While the number probably doesn’t mean much to you, several studies have estimated that radioactive decay currently produces a helium flux of 2,000,000 atoms each second for every square centimeter of the surface of the earth. 1-3
So what happens to this helium? Well, it rises in the atmosphere for a while, but it doesn’t rise indefinitely. After all, in order to actually escape the earth’s atmosphere, it must escape earth’s gravitational pull, and that’s hard to do. Just like a rocket needs a lot of energy to escape the earth and get into space, a helium atom must also have a lot of energy to escape into space. The most likely source of energy is the surrounding temperature. The hotter the surrounding temperature, the more energy the atoms (or molecules) have.
Now you are probably aware that the temperature of the atmosphere decreases with increasing altitude, which is why snow stays on the top of a mountain even in the midst of a hot summer. However, you might not realize that this trend doesn’t continue forever. In fact, as you reach the stratosphere, temperature increases with increasing altitude because of the ozone layer. Once you rise above the ozone layer, temperature begins to decrease with increasing altitude for a while, but then it reverses again, increasing with increasing altitude. By the time you reach the very upper reaches of earth’s atmosphere, the temperature ranges from about 1,300 to 1,800 degrees Celsius.4 Well, taking even the highest temperature, the rate at which this would allow helium to escape is ridiculously small – much smaller than the rate at which is it being produced.
What does this tell us? It tells us that helium is building up in the earth’s atmosphere. Just as the oceans are getting “saltier,” earth’s atmosphere is getting “heliumier.” Assuming there was absolutely no helium in the atmosphere when the earth was created, at the current rates of helium production and escape, it would take less than 2 million years to get the amount of helium that we see in the atmosphere today. Thus, if what we know of today’s helium production and escape are indicative of what has always been happening in earth’s history, the oldest the earth could be is 2 million years old. Obviously, if earth’s atmosphere actually started out with some helium in it, the maximum age of the earth would be even lower.
So the next obvious questions is, “Are today’s helium production and escape rates indicative of what has always been happening in earth’s history?” The answer to that question is definitely not. For example, the whole point of radioactive decay is to bring an unstable atom to stability. Thus, for the vast majority of radioactive atoms, their numbers decrease over time. This means that there was more radioactive decay (and hence more helium buildup) in the past than there is now. That, of course, would mean that the 2 million year figure is actually an upper limit and thus the earth is probably significantly younger than 2 million years old.
Now this method of measuring the age of the earth makes it into my “top five” because the one thing we know is that helium isn’t getting removed from the atmosphere by some unknown chemical reaction. For example, if you present the age of the earth as determined by the amount of sodium in the oceans to someone whose preconceived notions require an ancient earth, he or she will simply postulate that there is some as yet unknown physical or chemical process that is removing sodium from the ocean. While this is an argument from ignorance, it is still at least a way that someone committed to an old earth can “wriggle out” of the obvious conclusion given by the amount of sodium in the oceans.
Likewise, people who are desperate to believe in an ancient earth generally try to find another way for the atmosphere to lose helium. Since chemical reactions won’t work, they generally resort to more exotic processes. For example, helium atoms that find themselves near the poles of the planet and also happen to lose an electron can be accelerated into space by the earth’s magnetic field. This “polar wind” is one way that those who want to believe in an ancient earth try to get around the helium problem. However, a very thorough study showed that the rate at which helium escapes from the atmosphere this way is much lower than the rate at which it escapes using the energy from the surrounding temperature5, so that doesn’t provide a way out.
The way most adherents to an old earth want to explain away the helium content of the atmosphere is by solar wind sweeping. The solar wind is composed of charged particles that are “blowing” at the earth from the sun. They can actually deform the magnetosphere of the earth and whisk away atmospheric particles, including helium. Attempts to model how this might happen have shown that under the right conditions, and with the right number of solar flares, etc., it might be possible to increase the escape of helium into space enough to make the atmosphere consistent with an ancient earth6.
Is this the answer those who need to believe in an ancient earth are looking for? Well, the proposal is reasonable. Scientists certainly have seen the atmosphere lose helium as a result of large “burps” from the sun, but the amount is miniscule, and such large “burps” from the sun are rare. As a result, the model proposed has not been tested in any meaningful way. Right now, it is safest to look at the data we have, and since the loss of helium via this method is so small that we cannot even test the model, it is safest to assume that this is not the answer the old-earthers need. As an old-earther admitted in the journal Origins two years after the model was proposed,
The question of the rate of loss of helium to outer space remains an enigma. Several alternatives are possible. 7
In the paper, the author lists several alternatives, none of which he finds satisfactory. In fact, he thinks that solar wind sweeping gets rid of less helium than the polar wind, which he also agrees doesn’t get rid of enough helium to solve the problem. Noticeably absent among his list of alternatives, however, is the consideration that the earth might be young.
So…if you desperately need to believe in an ancient earth, you can believe an untested model that allows you to “wriggle out” of the obvious conclusion given by the helium data. However, if you are actually willing to consider the data objectively, the amount of helium in the atmosphere indicates that the earth is young.
1. MacDonald, G. J. F., “The escape of helium from the earth’s atmosphere,” Reviews of Geophysics and Space Physics 1:305–349, 1963.
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2. Axford, W. I., “The polar wind and the terrestrial helium budget,” Journal of Geophysical Research 73:6855–6859, 1968.
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3. Craig, H. and W. B. Clarke, “Oceanic 3He: Contribution from cosmogenic tritium,” Earth and Planetary Science Letters 10:289–296, 1970.
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4. John E. Frederick, Principles of Atmospheric Science, Jones & Bartlett Publishers, Inc., p. 20, 2007
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5. Axford, W. I., “The polar wind and the terrestrial helium Budget,” Journal of Geophysical Research, Space Physics , 73:6855-6859, 1968
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6. Lie-Svendsen, O. and M. H. Rees, “Helium escape from the terrestrial atmosphere – the ion outflow mechanism,” Journal of Geophysical Research, 101:2435-2443, 1996
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7. R.H. Brown, ” Unique Enigmatic Helium,” Origins , 25:55-73, 1998
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