Also known as "geological time", this refers to the period covering the physical formation and development of Earth, especially prior to human history.
Adapted from The American Heritage® Dictionary of the English Language, Fourth Edition

Glaciers are slow-moving "rivers of ice", and they give some idea of what the Earth looked like during one of the Ice Ages.

Tsunami is a Japanese word represented by two characters: "tsu" and "nami." The character "tsu" means harbor, and the character "nami" means wave. In the past, tsunamis were often referred to as "tidal waves." The term "tidal wave" is a misnomer. Tides are the result of gravitational influences of the moon, sun, and planets. Tsunamis are not caused by the tides and are unrelated to the tides.
from the National Tsunami Hazard Mitigation Program.