Final answer:
The method for placing rock units and geologic events in sequence without exact numerical ages is relative dating, using principles like stratigraphic superposition. Absolute dating provides numerical ages, often using radiometric techniques.
Step-by-step explanation:
The task of placing rock units and geologic events in their proper sequence is known as relative dating. This method does not provide numerical ages but rather the order in which events occurred. Relative dating utilizes principles such as the law of superposition, where the oldest strata are at the bottom, and the younger ones are on top.
Contrastingly, absolute dating is used to determine the numerical age of rocks and geologic events, often by using radioactive isotopes. Although absolute dating provides specific ages, relative dating is still widely used by geologists for its simplicity and applicability to various rock types.
One of the critical principles of relative dating is stratigraphic superposition, which applies to both geological and archaeological layers, suggesting that materials in lower strata are older than those in upper layers. However, absolute dating methods like radiometric dating assign a precise age to samples, crucial when exact dating is necessary.