300,000,000 B.C.

In the real world

 * Earth is in the Carboniferous era. In this era, trees and other giant plants successfully colonised the land, and many different species of giant insects evolved, including the ancestors and relatives to many modern insects.

In the Kaiju Multiverse

 * During the carboniferous, the Meganulon are among the strongest creatures alive. An egg containing large numbers of Meganulons is suddenly pulled through to 2000 as a result of the Dimension Tide's first test. (Godzilla vs. Megaguirus)