Which phrase describes the element carbon-14? decays at an unknown rate found in an organism’s remains forms from the breakdown of nitrogen-14 is measured to determine the age of sedimentary rocks
The Correct Answer and Explanation is :
The correct phrase that describes carbon-14 is:
“forms from the breakdown of nitrogen-14.”
Explanation:
Carbon-14 ((^{14}C)) is a radioactive isotope of carbon that is used in radiocarbon dating, which is a method for determining the age of objects containing organic material by measuring the amount of (^{14}C) they contain.
Here’s how carbon-14 is formed and why the statement “forms from the breakdown of nitrogen-14” is correct:
- Formation of Carbon-14:
Carbon-14 is created in the upper atmosphere through a process known as cosmic ray spallation. High-energy cosmic rays collide with nitrogen-14 ((^{14}N)), a stable isotope of nitrogen, causing it to undergo a nuclear reaction. This reaction results in the formation of a neutron that strikes (^{14}N), converting it into carbon-14 ((^{14}C)): [
^{14}N + \text{neutron} \rightarrow ^{14}C + \text{proton}
] This newly formed carbon-14 is then incorporated into carbon dioxide (CO2) in the atmosphere. Plants absorb this CO2 during photosynthesis, and animals ingest it when they eat plants or other animals. - Decay of Carbon-14:
Over time, carbon-14 decays through beta emission, where it transforms back into nitrogen-14. The half-life of carbon-14 is approximately 5,730 years, which makes it useful for dating objects up to about 50,000 years old. After an organism dies, it stops absorbing carbon, and the (^{14}C) in its remains begins to decay. By measuring the amount of remaining (^{14}C) in a sample and comparing it to the original amount, scientists can estimate the time since the organism’s death. - Other Options:
- “Decays at an unknown rate” is incorrect, as the decay rate (half-life) of carbon-14 is well-known.
- “Found in an organism’s remains” is true, but it doesn’t capture how (^{14}C) is formed.
- “Measured to determine the age of sedimentary rocks” is incorrect because carbon-14 is used to date organic material, not rocks, especially sedimentary rocks, which are often too old or lack sufficient organic material.
Thus, the statement that carbon-14 forms from the breakdown of nitrogen-14 is the most accurate.