Uniformitarianism is the principle or assumption that the same natural laws and processes that operate in the universe now have always operated in the universe in the past and apply everywhere in the universe.

In science, a half-life is the amount of time it takes for half of a substance or entity to undergo some specified process.

The major events in the geologic time scale include the formation of Earth, the development of life, mass extinctions, and the evolution of various geological eras, such as the Paleozoic, Mesozoic, and Cenozoic.

Pangaea, Laurasia, and Gondwana were ancient supercontinents that existed during different geological periods, with Pangaea being the most recent and comprising Laurasia in the northern hemisphere and Gondwana in the southern hemisphere.

The Hertzsprung–Russell diagram, or H–R diagram, is a plot of stellar luminosity against surface temperature.