Age of Earth: Uranium-Lead Dating, Samarium, Rubidium-Strontium

In summary, scientists use Samarium-neodymium and Rubidium-strontium to calculate the age of Earth because they are relatively stable and their amount grows with time. Potassium/Argon dating is a useful tool because it can be used to date rocks that have not been exposed to the atmosphere.
  • #1
ecksor
2
0
i am wondering if we know decays like Samarium-neodymium and Rubidium-strontium with half-lives of 106 and 49 billion years, why scientists consider the age of Earth based on Uranium-lead dating with half-life of 4.47 billion years? i mean if there wasn't Earth 100 billion years ago, where these Samarium comes from?
 
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  • #2
They are produced in radioactive decay from other elements/isotopes. As they are relatively stable, their amount grows.
 
  • #3
thanks
 
  • #4
Read more on half life here.
http://en.wikipedia.org/wiki/Half_life

Keep in mind that it is a probability that something will decay within this time frame. See #1 paragraph in the article.
 
  • #5
Also to date a rock their must be detectable amounts of both the parent and the daughter products, and you must be able to tell that the daughter products came from the parent product in the rock. Potassium/Argon dating comes to mind. Potassium is an element that can be found in quite a few minerals, especially the "K-feldspars" or potassium feldspars. K40 decays to Ca40 and Ar40. Only about 10.9% decays to argon but that is the element that geologists are interested in. The reason why is that there are usually other sources of calcium that make it very difficult to detect the calcium from radioactive decay. Argon on the other hand does not usually appear in rocks as part of the elements that make up its minerals so it is fairly safe to assume that it is a radioactive product. Potassium/Argon therefore is a very useful dating tool. You have an element that can be found in almost any rock and a daughter product that is not. The one concern is that you want material that has not been exposed to the atmosphere, since that can be a source of argon.

The main reason that I can see that samarium/neodymium is not used can be seen by what they call these elements. I know off of the top of my head that neodymium is a rare earth, and I am certain that samarium is one too. A daughter product that is rare is a good thing, that increases the odds that any daughter product you see is a result of decay, a parent material that is rare is a bad thing, that means it is highly unlikely that you will have any product to decay in the first place.
 
  • #6
Rare Earth's are not that rare. There are more rare Earth's than copper, zinc or chromium. There is more samarium than tin.

You are exactly right, though, that you want to pick an isotope with a half-life close to the age of your sample. If the half-life is too short, you have mostly daughter nuclei and not many parents, and if it's too long, you have mostly parents and not many daughters.
 

1. How does uranium-lead dating determine the age of the Earth?

Uranium-lead dating is a radiometric dating method that uses the decay of uranium and its eventual product, lead, to determine the age of rocks and minerals. The ratio of uranium to lead in a sample can be measured and used to calculate the age of the sample based on the known decay rates of these elements.

2. What is the significance of samarium in dating the age of Earth?

Samarium is a rare earth element that is often used in radiometric dating because it has a very long half-life (the time it takes for half of the atoms in a sample to decay). This makes it a useful tool for dating very old rocks and minerals, such as those found on Earth.

3. How does rubidium-strontium dating work to determine the age of the Earth?

Rubidium-strontium dating is another radiometric dating method that uses the decay of rubidium-87 to strontium-87 to calculate the age of rocks and minerals. The ratio of these two elements in a sample can be measured and used to determine the age of the sample based on their known decay rates.

4. Can uranium-lead dating be used to determine the age of all rocks?

No, uranium-lead dating is only useful for dating rocks that contain uranium and have not been significantly altered or contaminated since their formation. This method is most commonly used for dating igneous rocks, but can also be used for some metamorphic rocks.

5. How accurate is the age determination using these dating methods?

Radiometric dating methods, including uranium-lead dating, samarium dating, and rubidium-strontium dating, are generally very accurate within a certain range. The accuracy depends on several factors, including the initial conditions of the sample, the preservation of the sample, and the precision of the measurement techniques. Generally, these methods can provide reasonably accurate age estimates within a few million years for rocks that are billions of years old.

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