Types of radioactive dating methods
After another half-life, there is 1/2 of that 1/2 left = 1/2 × 1/2 = 1/4 of original amount of the parent left.
After yet another half-life, there is 1/2 of that 1/4 left = 1/2 × 1/2 × 1/2 = 1/8 of the original amount of the parent left (which is the fraction asked for).
Carbon-14 dating works well for samples less than about 50,000 to 60,000 years old and for things that were getting their carbon from the air.
The long ages (billions of years) given by radioactive dating of rocks seems an impossibly long time for some people.
All atoms of an element have the same number of protons in their nucleus and behave the same way in reactions.
The atoms of an isotope of a given element have same number of protons AND neutrons in their nucleus.
The discussion above is for the case of determining when a ) are the radioactive carbon-14 isotope that will decay to form nitrogen-14 with a half-life of 5,730 years.
To measure the passage of long periods of time, scientists take advantage of a regularity in certain unstable atoms.Different isotopes of a given element will have the same chemistry but behave differently in Radioactive isotopes will decay in a regular exponential way such that one-half of a given amount of parent material will decay to form daughter material in a time period called a half-life. When the material is liquid or gaseous, the parent and daughter isotopes can escape, but when the material solidifies, they cannot so the ratio of parent to daughter isotopes is frozen in.The parent isotope can only decay, increasing the amount of daughter isotopes. The number n is the number of half-lives the sample has been decaying.Isotopes of a given element have the same chemical properties, so a radioactive rock will incorporate the NONradioactively derived proportions of the two isotopes in the Multiply the amount of the non-daughter isotope (isotope B) in the radioactive rock by the ratio of the previous step: (isotope B) × R = initial amount of daughter isotope A that was not the result of decay.
Subtract the initial amount of daughter isotope A from the rock sample to get the amount of daughter isotope A that IS due to radioactive decay.
Since radioactive rocks have been observed for only a few decades, how do you know you can trust these long half-lives and the long ages derived?