Question

the
radiation era
matter era
occured first. this event is when
happened. the second era was

Explanation:

To solve this, we recall the chronology of cosmic eras:

Step 1: Identify the first era

In cosmic history, the Radiation era occurred first. This era was dominated by high - energy radiation (like photons) and lasted from the Big Bang until matter (particles like protons, neutrons, electrons) became dominant.

Step 2: Identify the second era

After the Radiation era, the Matter era began. In the Matter era, matter (both ordinary and dark matter) became the dominant component of the universe, allowing for the formation of structures like galaxies, stars, and planets.

Answer:

First dropdown (era that occurred first): Radiation era
Second dropdown (era that came after): Matter era

(Note: The specific context of the middle dropdown (describing the event) would relate to the transition or key events of the Radiation era, such as the dominance of radiation over matter in the early universe, but based on the era order, the first era is Radiation era and the second is Matter era.)