Era

Example:

Imagine trying to organize a massive photo album that spans multiple generations of family events. Just as you would divide the album into smaller sections for each family member's life stages or significant events, geologists divide this era, the second-longest unit of geologic time, into smaller periods to make it easier to understand Earth's history. Just like each section of the album captures a specific phase or milestone in your family's story, each period within this era encapsulates distinct geological and biological changes on Earth, helping scientists piece together the planet's vast timeline.