K ar dating method ppt

22-Dec-2019 11:20 by 9 Comments

K ar dating method ppt

When a rock undergoes metamorphism, some or all of its argon can be outgassed.If all the argon was lost, this would reset the K-Ar clock to zero, and dating the rock would give us the time of metamorphism; and if we recognized the rock as metamorphic this would actually be quite useful.

When the rock recrystallizes it becomes impermeable to gasses again.

(However, see the section below on the limitations of the method.) This suggests an obvious method of dating igneous rocks.

If we are right in thinking that there was no argon in the rock originally, then all the argon in it now must have been produced by the decay of Ar in them will be so small that it is below the ability of our instruments to measure, and a rock formed yesterday will look no different from a rock formed fifty thousand years ago.

However, we cannot rely on all the argon being lost, and if it is not then when we apply K-Ar dating this will give us an essentially arbitrary date somewhere between the formation of the rock and the metamorphosis event.

For these reasons K-Ar dating has largely been superseded by Ar-Ar dating, which will be the subject of the next article.

But consider what happens if the argon came from deep within the Earth, where it was formed by Ar ratio as is found in the atmosphere, and the formula that corrects for atmospheric carbon will not correct for this.

Finally, we must consider the possibility of argon loss.Argon, on the other hand, is an inert gas; it cannot combine chemically with anything.As a result under most circumstances we don't expect to find much argon in igneous rocks just after they've formed.As with any dating technique, there are some significant limitations.Ar) dating is a radiometric dating method invented to supersede potassium-argon (K/Ar) dating in accuracy.K has a half-life of 1.248 billion years, which makes it eminently suitable for dating rocks.