Question

based on their descriptions, why would geologists use both relative and absolute dating to reconstruct earths history?
to make sure the absolute age is correct by checking it against the relative age.
to place rock layers in the correct order first and then assign specific dates to key events.
to find the relative age of the oldest rock layer only.
to use absolute dating on every single rock layer in a sequence.

Explanation:

Relative dating first establishes the sequential order of rock layers and geological events without specific numerical ages. Absolute dating then provides exact numerical dates for key layers or events, combining the two creates a complete, accurate timeline of Earth's history. The other options are incorrect: cross-checking is not the primary purpose, relative dating applies to more than just the oldest layer, and absolute dating is not feasible for every single rock layer.

Answer:

To place rock layers in the correct order first and then assign specific dates to key events.