Final answer:
K-Ar dating is unsuitable for environments where rocks have been exposed to atmospheric argon or have been altered, potentially affecting the Ar-40:K-40 ratio used for dating; under such circumstances, uranium-lead or rubidium-strontium dating methods are preferred for their reliability.
Step-by-step explanation:
Potassium-Argon (K-Ar) dating cannot be used in environments where the rock samples may have been exposed to argon in the atmosphere or where the rock was altered and had either potassium or argon added or removed after its initial formation. An example of this might be weathered or hydrothermally altered rock. Since K-Ar dating relies on the accurate measurement of the Ar-40:K-40 ratio, the presence of atmospheric argon or alteration of the rock can lead to inaccurate results. In such cases, an alternative method such as uranium-lead dating, which uses the radioactive decay of uranium-238 to lead-206, or rubidium-strontium dating, which uses the decay of rubidium-87 to strontium-87, might be utilized. These methods are considered more specific or reliable under the conditions where K-Ar dating is not appropriate. Uranium-lead dating is particularly useful for dating the age of some of the oldest rocks on earth.