Why are time periods on the geologic time scale not even in length? pick one

Question

Responses

They are based on the type of fossils found in rock layers of the Earth.
They are based on the type of fossils found in rock layers of the Earth.

They are based on important events that happened in Earth’s history.
They are based on important events that happened in Earth’s history.

They are based on the thickness of the Earth's rock layers.
They are based on the thickness of the Earth's rock layers.

They are based on a different type of calendar used to track Earth’s history.

Answer 1

They are based on important events that happened in Earth’s history. Time periods on the geologic time scale are often defined by major geological or biological events that marked significant changes in the Earth's history. This can result in time periods of varying lengths, as these events were not necessarily evenly spaced out over time.