radioactive materials have halflife of 50000 years how can the planet be 3 billion years old if so where doe?

Question

where does the new radioactive stuff come from

Answer 1

First of all, you have to understand what 'half-life' means.

Breakdown of a radioactive nucleus is essentially unpredictable. Nobody can look at ONE atom and say, "it will break apart at exactly this time". On the other hand, there IS an overall pattern of when they tend to break down. If you have a billions and billions of atoms, you may not know when any particular one has gone, but the amount of time for half of them to go is usually pretty constant. This is the half-life.

So if you start with 1000 pounds of something with a half-life of 50000 years, after 50000 years, you'll have 500 pounds of that stuff, and a bunch of whatever it decayed into. In another 50000 years you'll have only 250 pounds. And so on. Given how small atoms are, it's going to take AT LEAST eighty halving until you get down to the last atom. And that's four billion years right there.

And that just assumes arbitrarily that there was only 1000 pounds of the stuff to begin with. The Earth is at least a billion billion times that large - so if even 1% of it was made of this particular radioactive element to begin with, there would still be tons lying around today.

Another very important factor is what, exactly, radioactive materials decay into. In most cases, they turn into DIFFERENT radioactive materials!

Take the example of radium. It has a half-life of about 1600 years, and can be found in the soil in some places. When it decays, radium becomes into radon, which is a noble gas. As a gas, it bubbles out of the ground and into the atmosphere. The most stable form of radon has a half-life of only three days. Then it turns into polonium with a half-life of three minutes, and then a radioactive form of lead, and so on and so on.

The above actually happens quite freqently, and has come to be a not uncommon danger to homeowners in some areas as the gas bubbles into their house, turns into dust on their bodies and food, and then proceeds to irradiate those who live in the home. And though you might think the short half-life of radium would mean there's not much of it around, it actually ultimately comes from uranium, which has a half-life of four billion years.

So new supplies of most radioactive materials are CONSTANTLY being produced from the vast amounts of uranium which can be found in the Earth. And uranium has such a ridiculously long half-life that it's probably far more likely that there are no humans before there is no uranium...

Answer 2

1) "Radioactive materials have halflife of 50000 years"
This is not exact. SOME radioactive materials have halflife of 50000 years. Some others have 1/2 life of 0.5 seconds and some of 3 billion years. U238 has quite long half life (4.5 billion years!)

2) This is 1/2 life. A material has half-life of 50,000 years means that HALF of it decayed in 50,000 years. And the half of what is left in the next 50,000. And so on. After 100,000 years you still have 1/4 of the origine material, after 200,000 years you have 1/16 left.

3) when the materials decays, it is often left another radioactive material, for which the life begins at that time...

Answer 3

Your thinking is correct, but your information on halflives is wrong.

Uranium-235's decay to Lead-207 has a halflife of 700 million years.
Uranium-238's decay to Lead-206 has a halflife of 4.5 billion years.
Rubidium-87's decay to Strontium-87 has a halflife of 50 billion years.

Obviously, the existence of U235, U238 etc. is entirely compatible with a 4.5 billion year old earth.

There are many short-lived radioactive materials, of course. As a rule, these can't be found in nature, except in cases where there's a source of new short-lived material (for example when a radioactive material with a long half-life decays into one with a short half-life).

Answer 4

It comes from the decay of other radioactive substances that have longer half lives. Also, some radioactive materials are created by cosmic rays striking other materials and transmuting them into radioactive substances.

Answer 5

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Answer 6

It comes from the breakdown of other radioactive material *or* it is man made in a particle accelerator.

Answer 7

the more radioactive element that is together, the longer the energy lasts