Recently in this forum I wrote about nuclear science in Serbia, and Serbian scientific work on the origins of the earth.
The fun part of that thread involved a discussion of plutonium-244 that was originally present on the earth. All of this plutonium has now decayed to thorium at least - thorium being the element that is the last best hope of the human race - and some of it has decayed to lead-208, which is of course, not radioactive.
This discussion stimulated me to open up some papers in my files that I haven't opened in a while, and the ones I'd like to discuss here are two papers in a journal I always enjoy reading when I have time - which I don't have often enough - Earth and Planetary Science Letters, particularly the "origins" papers.
First let me get my sarcasm and derision out of the way.
I often note the um, "intellectual" - if you want to call it "intellectual" - similarity between creationism and the notion that nuclear science, the science of Rutherford and Bohr and Seaborg, is intrinsically evil. Almost always the people attaching negative moral values to knowledge itself, be it genetics, evolutionary biology or nuclear science, are appealing
baldly to ignorance itself. I also note that a knowledge of nuclear science is
essential to our understanding of the origins of this planet and on a broader scale, the origins of the universe as a whole.
Anyway.
The first paper I'd like to discuss is "Xenon compositions of magmatic zircons in 3.64 and 3.81 Ga
meta-granitoids from Greenland: a search for extinct 244Pu in ancient terrestrial rocks."
Here is the abstract:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-47TX1G4-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=986416613&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=08f3a86082e0c4a17c0ecf64b52b09eb">Earth and Planetary Science Letters 207 (2003) 69-82
The authors have examined some very old rocks in Greenland, some of the oldest rocks on earth (the oldest - determined by their Rb-87/Sr-87 ratios - are in Canada and in Australia) to determine the composition of the noble gas xenon, specifically its isotopic ratios.
A fun excerpt from the paper body:
Isotope geochemistry allows us to constrain the timing of geological events and provides tracers of the processes which have formed and continue to modify the Earth. In this regard, the abundances and isotopic compositions of the noble gases (helium, neon, argon, krypton and xenon) from terrestrial samples provide useful and unique information concerning the origin and evolution of the Earth including its differentiation into the core, mantle, crust and atmosphere. It is important to know noble gas compositions in the past in order to re¢ne models of the evolution of the Earth and its atmosphere. Xenon isotope compositions of Archaean samples can potentially be useful, as these samples may retain records of now extinct nuclides such as 129I and 244Pu (129I decays to 129Xe with a half-life of 16 million years <1>, and 244Pu decays with a half-life of 82 million years; and produces spontaneous fission xenon isotopes <2>).
It is generally believed that the Earth’s atmosphere was formed by signi¢cant degassing of volatiles from the Earth, and that this degassing occurred at an early stage of the Earth’s formation (e.g. <3>). Of the total xenon in the Earth’s atmosphere, 6.8% of atmospheric 129Xe is estimated to be 129I-derived radiogenic 129Xe <4>. Similarly it has been argued that 4.7% of atmospheric 136Xe is fissiogenic xenon which is attributed to spontaneous fission of the extinct nuclide 244Pu (plutogenic) <4>.
At the risk of hearing from a stupid person about how I applaud thyroid cancer, I note that I-129 is now found on earth as a fission product from the operation of nuclear reactors. Because of its long half life it is not particularly radioactive, and it represents essentially zero risk. It is, in theory, easy to contain this iodine essentially forever simply by collecting mercury from dangerous fossil fuel waste, since mercurous iodide is one of the most insoluble materials known, but the risk of this isotope is extraordinarily low that it is not worth the money, particularly when the money could be spent on doing something other than satiatiating the irrational (and insatiable) paranoia of anti-nukes, like providing health care for uninsured children for instance. Spending one billion dollars to contain I-129 forever will save zero lives, since zero lives were at risk, whereas spending one billion dollars for health care will save thousands of lives.
(I wrote in some more detail about I-129 on another website is a piece I called
http://www.dailykos.com/story/2007/1/3/152128/3838">Radioactive Isotopes from French Commercial Nuclear Fuel Found In Mississippi River. )
So there you have it folks. It turns out that your, atmosphere, is (oh my god!) the result of nuclear decay of
radioactive stuff, including, um, plutonium.
The second paper I'd like to mention that is a fun read is "Geochemical constraints on mantle dynamics in the Hadean"
Here's the abstract:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4GY878C-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=986432505&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=40e93286c3b907f76710103cc997e23d">Earth and Planetary Science Letters 238 (2005) 17– 30
The early evolution of the Earth during the Hadean (4.5–3.8 Ga) is poorly known. A short time scale of Earth differentiation is consistent with a 182Hf–182W age of 45F4 Myr for the end of Lunar differentiation <1>. 182Hf–182W (T 1/2 = 9 Myr) extinct radioactivity indicates that the Earth formed and differentiated within a time interval of a few tens of Myr <2,3>. Anomalies of 142Nd produced by 146Sm (T 1/2 = 103 Myr) found in Archean volcanic rocks <4–6> as well as initial 143Nd/ 144Nd ratios suggest early and intensive differentiation of the terrestrial mantle within the first 200 Myr after start of the solar system condensation (ASSC). Because mantle degassing requires magmatism, noble gas isotopes can also provide important clues on the thermal evolution of the Earth. In particular, the isotopic composition of xenon presents a powerful mean to investigate the early evolution of planetary bodies. Some of the Xe isotopes are produced by three radioactivities having contrasted half-lives: the b-decay of 129I produces 129Xe with T 1/2 = 15.7 Myr, the spontaneous fission of 244Pu produces 131136Xe with T1/2 = 82 Myr, and the still active spontaneous fission of 238U also produces 131136Xe with T 1/2 = 4.45 Gyr. These contrasted half-lives allow investigation of terrestrial degassing during the accretional period, the Hadean, and from the Archean to present, respectively (e.g., <7–13>). Studies of Xe isotopes in the atmosphere and the mantle have shown that terrestrial reservoirs have extensively lost volatile elements. The depletion of Xe isotopes produced by extinct radioactivities in the mantle can be demonstrated as follows...
Pure nuclear science.
Before he died, the great
nuclear chemist, and Nobel Laureate and
Democrat Glenn Seaborg, the only person
ever to have had an element in the periodic table named for him
during his life time warned of the risk of scientific ignorance (including of course, nuclear science ignorance) to our economy in the United States.
Nuclear science, vilified by the purveyors of ignorance, is at serious risk in this country. I never stop noting that more than half of the nuclear chemistry Ph.D's - numbering only 100 a year - are foreign born and are not native English speakers in general.
Of course this is a tremendous risk to both our economy and our environment, but it is also a risk to our knowledge of
who we are and where we come from.
That, I think, is very sad, as sad as the fact that the nation of Rutherford, New Zealand, and the nation of Bohr, Denmark are both officially anti-nuke countries.
Ignorance kills.
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