The Earth’s Geologic Time Scale Eons Eras Periods …
Geologic time scale - Wikipedia
Four major divisions
Roughly, we can divide the time column into units comprehensible to us by saying the Cenozoic was the past time from present day back to the disappearance of the dinosaurs. The Mesozoic was the time that dinosaurs lived, the Paleozoic was before the dinosaurs with fossil plants and sea animals, and the Precambrian is the oldest group of rock: mysterious because so little is known about it. And get a load of this: Precambrian time occupies eighty percent of the earth's history!
On the previous page, we told you some of the active processes that assist the continents in their slow-motion dance around on the planet's surface, bumping and banging together (called plate tectonics), creating mountains when they collide. Volcanoes and erosion are also active forces that shape the land. Volcanoes bring up new material for land, erosion wears it down. That's part of the rock cycle.
Geologic Time Scale: Major Eons, Eras, Periods and Epochs
The table of geologic time spans presented hereagrees with the dates and nomenclature proposed by the International Commissionon , and uses the standard color codes ofthe United States Geological Survey.