- Solar System Objects
- Planetary Objects
- Planetary Processes
- Planetary Miscellaneous
1. How do scientists find the age of planets (date samples) or planetary time (relative age and absolute age)?
2. Why is it important to establish the age of a planet?
3. How do you technically define half-life?
4. If carbon-14 is so short-lived in comparison to potassium-40 or uranium-235, why is it that in terms of the media, we mostly about carbon-14 and rarely the others?
5. Is there a chemical test for carbon?
6. Are carbon isotopes used for age measurement of meteorite samples? We hear a lot of time estimates, X hundred millions, X million years, etc.
|Parent||Daughter||Half-Life (billion years)|
|Carbon-14||Nitrogen-14||0.0000057 (5730 yrs)|
7. How is radioactive decay used to date a surface?
In nature, all elements have atoms with varying numbers of neutrons in their nucleus. These differing atoms are called isotopes and they are represented by the sum of protons and neutrons in the nucleus. Let's look at a simple case, carbon. Carbon has 6 protons in its nucleus, but the number of neutrons its nucleus can host range from 6 to 8. We thus have three different isotopes of carbon: Carbon-12 with 6 protons and 6 neutrons in the nucleus, Carbon-13 with 6 protons and 7 neutrons in the nucleus, Carbon-14 with 6 protons and 8 neutrons in the nucleus. Both carbon-12 and carbon-13 are stable, but carbon-14 is unstable, which means that there are too many neutrons in the nucleus. Carbon-14 is also known as radiocarbon. As a result, carbon-14 decays by changing one proton into a neutron and becoming a different element, nitrogen-14 (with 7 protons and 7 neutrons in the nucleus). The isotope originating from the decay (nitrogen-14 in the case of radiocarbon) is called the daughter, while the original radioactive isotope (like carbon-14) is called the parent. The amount of time it takes for an unstable isotope to decay is determined statistically by looking at how long it takes for a large number of the same radioactive isotopes to decay to half its original amount. This time is known as the half-life of the radioactive isotope.
Once the half life of an isotope and its decay path are known, it is possible to use the radioactive decay for dating the substance (rock) it belongs to, by measuring the amount of parent and daughter contained in the sample. An important point is that we must have an idea of how much of the daughter isotope was in the sample before the decay started.