Radioactive material as it relates to Earth

[Aquafire]

How long does radiactive material remain radioactive.?

I ask this in light of the issue of Earth's core heating.

It seems to me the radioactivity model has to explain how such material remains seemingly radioactive to this day. 4.5 billion years after the Earth was formed.

Does that defy what we know of material such a uranium etc all of which lose radiactivity over a relatively short period of time compared to the Earth's entire geological history. ?

Or am I mistaken in my understanding of these things ?

Aquafire

 

[Andre]

Good questions Aquafire.

We can explain things for hours talk about Uranium Thorium series, Kalium Argon series, the thermo geo nucleair reactor but in the end the answer is: we don't know we can just speculate. Do you want a higher level of ignorance?

 

[Monique]

Originally posted by Andre
Kalium Argon series

Kalium = Potassium :P

What I could find on the net is that the isotope with the longest known half-life is tellur-128 (1.5 E24 years) and with the shortest is radium-216m (7E-9 s = 7 ns). Don't ask me how it is related to the Earth model though :) it just demonstrates the limits.

 

[Monique]

About elements with a very long half-life.. this is interesting to consider:

Is it possible that every isotope is radioactive but that decay is so infrequent as to be immeasurable??

-----Original Message-----
From: Jerry Cohen [mailto:jjcohen@PRODIGY.NET]
Sent: Friday, April 25, 2003 11:26 AM
To: John Jacobus; radsafe
Subject: Re: Bismuth breaks half-life record

It is hard for me to conceive of anything with a half-life of ~10^19 years as "radioactive". Given enough time, all matter will eventually decay, since the proton itself is reputed to decay with have a half-life of ~10^31yr. Therefore, in a sense, everything could be considered "radioactive" (i.e. no such thing as a stable element). It is also hard to understand the special dread of long-lived radionuclides given that the longer the half-life, the less radioactive anything is.
To avoid such perceptions, in a paper we gave about 20 years ago, we proposed the radioactive designation be limited to those nuclides with half-lives less than one million years. Those with half-lives between a million and a trillion years would be "radiopassive", and those with a half-life exceeding a trillion years would be designated "radioquiscent".
Somehow, the idea never caught on.

http://www.vanderbilt.edu/radsafe/0304/msg00357.html

 

[russ_watters]

Originally posted by Aquafire
How long does radiactive material remain radioactive.?

I ask this in light of the issue of Earth's core heating.

It seems to me the radioactivity model has to explain how such material remains seemingly radioactive to this day. 4.5 billion years after the Earth was formed.

Does that defy what we know of material such a uranium etc all of which lose radiactivity over a relatively short period of time compared to the Earth's entire geological history. ?

A quick goole will tell you the half life of any element (isotope). Have a look at THIS

Uranium 238 - Uranium Series 99.2745% of all natural uranium...4.47 billion years half life

So over the age of the Earth, roughly half of all the U238 that existed at the Earth's formation has decayed.

 

[Nereid]

AFAIK, the most important elements/isotopes - re heating the Earth - are uranium, thorium and potassium-40. Why? A combination of abundance and long half-life.

Did you know there was once a natural reactor right near the surface of the Earth?

 

[Andre]

I ask this in light of the issue of Earth's core heating.

We have had a long discussion of the heating of the Earth core here

I suggested that radio-activity may not necesarily be a (main) player. It could be friction instead. Here is somebody who thinks likewise:

http://www.informnauka.ru/eng/2002/2002-06-28-02_146_e.htm

An Irkutsk geologist has suggested that our planet's heat source is friction in the outer core. The outer core is a huge liquid area, divided into many layers, which move with different speeds in different directions, thus causing friction between them and heat.