Question

1. when does a new era start?

○ it starts based on when new mammals appeared in the timeline.
○ the eras start at random intervals.
○ it starts when something new occurs in the geologic timeline.
○ a new era starts every billion years.

Explanation:

Geologic eras are defined by major shifts in Earth's geology, climate, or the dominant life forms (such as mass extinctions or the emergence of key organisms). They do not follow fixed time intervals, random timing, or a single event like mammal appearance. Instead, they begin when significant new developments in the geologic or biological record take place.

Answer:

It starts when something new occurs in the geologic timeline.