The Solid Earth - Chapter 9: Radioactivity and Radiometric Dating Flashcards
We know that the earth is 4.6B years old and that the dinosaurs became extinct about ___ years ago
66 million
True or false: a neutron is technically a proton and electron combined
True
In some isotopes, the ____ is unstable
nucleus
What is an isotope?
An atom with different numbers of neutrons in the nucleus
This results when the nuclei spontaneously break apart (decay)
radioactivity
Name three types of radioactive decay
Alpha particles emitting from the nucleus
Beta particle or electron given off from nucleus
Electron captured by nucleus (combined with proton and forms neutron)
The radioactive isotope is referred to as the ____
parent
The isotopes resulting from the decay of the parent are termed the ____
daughter
What is the process called whereby radioactivity helps calculate the age of rocks and minerals containing particular radioactive isotopes
radiometric dating
Each radioactive isotope used for dating has been decaying at a ___ rate since the formation of the rocks in which it occurs and the products of decay have been accumulating at a corresponding rate
fixed
The time required for one half of the nuclei in a sample to decay which is a common way of expressing the rate of radioactive disintegration
half life
When the quantities of parent and daughter are ___ (1:1) we know that one half life has transpired.
equal
How do we know that two half lives have passed?
One quarter of parent remains and three quarters have decayed to the daughter product (ratio 1:3)
After three half lives, the ratio of parent to daughter atoms is ___
1:7
True or false: if the half life of a radioactive isotope is known and the parent/daughter ratio can be determined the age of the sample can be calculated
True
As the percentage of radioactive parent atoms ____, the proportion of stable daughter atoms ____
declines
rises
What is something used to make sure that radiometric dates are meaningful?
cross checks
What radioactive isotope is used to date very recent events?
Carbon - 14
What is another name for Carbon-14?
radiocarbon
What is the half life of Carbon-14?
5730 years
True or false: all organisms contain a small amount of carbon-14
True
When a plant or animal dies, the amount of carbon-14 gradually decreases as it decays to ___
nitrogen
Describe Carbon-12
the stable and most common isotope of carbon
