Radioactives Missing From The Earth

The 84 elements found on Earth occur as 339 isotopes. Only 269 of these are stable, and the other 70 are radioactive. An additional 1650 radioactive isotopes have been created in nuclear reactors and in particle accelerators.

The following is a table of all 29 known radioactive isotopes that have a half-life of one million years or more, and that are not being continually produced by natural nuclear reactions. It has been sorted in order of half-life. For each isotope, the table shows whether it is one of the ones found on Earth.

Isotope Half-Life
Found on
Vanadium 50 6,000,000,000 yes
Neodymium 144 2,400,000,000 yes
Hafnium 174 2,000,000,000 yes
Platinum 192 1,000,000,000 yes
Indium 115 600,000,000 yes
Gadolinium 152 110,000,000 yes
Tellurium 123 12,000,000 yes
Platinum 190 690,000 yes
Lanthanum 138 112,000 yes
Samarium 147 106,000 yes
Rubidium 87 48,800 yes
Rhenium 187 43,000 yes
Lutetium 176 35,000 yes
Thorium 232 14,000 yes
Uranium 238 4,470 yes
Potassium 40 1,250 yes
Uranium 235 704 yes
Samarium 146 103 no
Plutonium 244 82 by extreme effort
Curium 247 16 no
Lead 205 15 no
Hafnium 182 9 no
Palladium 107 7 no
Cesium 135 3 no
Technetium 97 3 no
Gadolinium 150 2 no
Zirconium 93 2 no
Technetium 98 2 no
Dysprosium 154 1 no

The thing to notice is that this list falls naturally into two halves. Short-lived radioactives are suspiciously absent from the Earth. If we had carried this list all the way down to 1,000 year half-lives, the block of no's would be 37 long instead of 10 long.

The most obvious explanation for the above is that all these elements were present when the Earth was formed, but by now the short-lived ones have decayed away. This explanation is compatible with the age scientists accept for the Earth.

Of course, nothing about this list really proves that the Earth is old. But the list is exactly what we would expect if the Earth is old, and it is a very puzzling list if the Earth is young.


In short, the cutoff point in the list is consistent with 4.55 billion years.


The Age Of The Earth, pages 80 and 376-387. However, I have used a more recent measurement of Samarium 146's half life: see WebElements and Brookhaven National Labs.

Detection of Plutonium-244 in Nature, Hoffman et al, Nature 234,132-134 (19 November 1971)

Last modified: 30 July 2000

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