Question

why is the isotope carbon - 14 used to determine the absolute age of once living organisms? carbon - 14 is used to date all rocks and fossils. carbon - 14 is not used to determine the absolute age of once living organisms. all living organisms contain carbon and the carbon - 14 begins to decay when the organism dies. carbon - 14 has a short half - life so it is better to use on younger fossils.

Explanation:

Carbon - 14 is an isotope of carbon. All living organisms take in carbon (including carbon - 14) during their life. When an organism dies, it stops taking in new carbon - 14, and the carbon - 14 in its body begins to decay. By measuring the amount of carbon - 14 remaining in a once - living organism (such as a fossil), scientists can calculate how long it has been since the organism died. This is the principle of radiocarbon dating.

Option 1: Carbon - 14 is not used to date all rocks. Igneous and metamorphic rocks are not suitable for carbon - 14 dating as they do not have the right carbon content from living organisms in the way that once - living organisms (and some sedimentary rocks with organic matter) do.
Option 2: This is incorrect as carbon - 14 is used for dating once - living organisms.
Option 4: While it is true that carbon - 14 has a relatively short half - life (about 5730 years), this is not the main reason for its use in dating once - living organisms. The key is the uptake and decay process related to living organisms.

Answer:

C. All living organisms contain carbon and the carbon - 14 begins to decay when the organism dies.