Young Earther Question

[Naturalist]

I'm not a YEC, but I can't figure this out:

 

Q1. Wouldn't an age of billions of years cause the earth's magma to run out of radioactive isotopes?

 

C1. One would think so. (Otherwise, a mechanism to replenish the radioactive isotopes would have to be found.) However, newly-formed rocks continue to contain radioactive isotopes.

 

Q2. What would happen if pure radioisotope samples were generated?

 

C2. There would be a gradually-increasing rate of decay. This would self-limit as the decay rate would make the sample less pure. The rate of accumulation of the isotope and the rate of its decay are factors that offset one another. If the rate of accumulation is nearly instantaneous, and the mass were large enough, there would be detonation. Otherwise, the sample would merely show an artificially-old age. Of course, as the purity goes down, assuming constant mass of the isotope, the rate of decay would decrease. However, if the sample were exposed to a second large radioactive sample of high purity, the original sample would show an artificially-old age.

[insane_alien]

thats poor understanding of radiation. even less than you can learn from a glance.

 

1/ some isotopes have halflifes in the billions of years. 1 even has a halflife longer than the age of the universe.

 

2/ it would be a decreasing rate of decay actually. the rest is bunk.

[YT2095]

(Otherwise, a mechanism to replenish the radioactive isotopes would have to be found.)

 

look up Breeder Reactors, and decay chains.

[lucaspa]

I'm not a YEC, but I can't figure this out:

 

Q1. Wouldn't an age of billions of years cause the earth's magma to run out of radioactive isotopes?

 

In fact, Naturalist, if you look at the radioisotopes that can't be produced by decay from other isotopes, the earth only has those long-lived nucleotides:

 

There are 64 nuclides that have half-lives in excess of 1,000 years. Of these, 47 have half-lives in the range 1,000 to 50 million years. Seven must be excluded from this analysis because they are being generated by interaction with cosmic rays or the decay of other nuclides. If the earth were new (within 10,000 years) then there should be significant amounts of all 40 nuclides in the earth's crust. If, on the other hand, the earth is billions of years old, then these 40 nuclides should have decayed, leaving no trace. We would then be able only to find nuclides with very long half-lives. So how many of the 40 short half-lived nuclides can we find in the crust? None. Zip. Of the 17 nuclides with half-lives greater than 50 million years, we can find detectable amounts of all 17.

 

Q2. What would happen if pure radioisotope samples were generated?

 

C2. There would be a gradually-increasing rate of decay. This would self-limit as the decay rate would make the sample less pure. The rate of accumulation of the isotope and the rate of its decay are factors that offset one another. If the rate of accumulation is nearly instantaneous, and the mass were large enough, there would be detonation. Otherwise, the sample would merely show an artificially-old age. Of course, as the purity goes down, assuming constant mass of the isotope, the rate of decay would decrease. However, if the sample were exposed to a second large radioactive sample of high purity, the original sample would show an artificially-old age.

 

This makes no sense. The decay rate is constant, with each isotope having its own half-life, but the rate of decay of that isotope never changes. Also, only a few radioisotopes have fission ("detonation"). What happens for those radioisotopes generated by other means -- such as C14 from N14 in the atmosphere -- you eventually reach an equilibrium where the rate of decay = rate of formation.