Dating Igneous Rocks
A Scientist using carbon 14 dating is actually measuring the?
age of the earth
age of igneous rock
time of death of a living thing
time an artifact was made
Shanna and Geo06 have got this just about right. The only thing I can add is that radiocarbon dating can not be used for more than about 70,000 years ago, and is more accurate for living things that died within the last 8,000 years.
Most geologists measure rock ages in millions, or even billions, of years, so the age of the earth and the age of almost all igneous rocks is well beyond the range of carbon dating. On top of that, igneous rocks contain very little if any carbon, so carbon dating is not applicable here.
So the only thing carbon 14 can be used for is to determine the time that an exchange of carbon with the atmosphere stopped, ie, the death of a living thing – the third item on your list of choices for your homework.
The half life of C-14, the radioactive isotope of carbon, is about 5730 years. Therefore, if you know the ratio between C-14 and C-12 in the atmosphere when the organism died, and you know the ratio now, the difference in the ratio can be calculated backwards, using the half life, to estimate when the organism died.
Atmospheric C-14 has not been in a constant ratio with C-12, as previously thought, so there are some serious problems with the accuracy of C-14 dating. The problem is that the natural ratio of the carbon isotopes in the atmosphere (carbon dioxide) varies because cosmic ray bombardment of the outer atmosphere produces C-14 but not C-12. The ratio can be predicted accurately using the ratios in old trees, where the tree rings can be used to accurately determine the age of each ring with its annual ratio, with a maximum of about 8,000 years -that’s how old the oldest trees are which can establish a reference ratio.
Dating of artifacts is a best guess, the best method is to measure the amount of lichens growing on them, or the age of carbon in ashes found in the same spot.
Are Rocks Accurate for Dating?
