National geographic earth history timeline
National geographic earth explorer.
Timeline of natural history
See also: Geologic time scale and Timeline of the evolutionary history of life
For earlier events, see Timeline of the early universe.
Main articles: History of the Earth and Geological history of Earth
This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans.
Times are listed in millions of years, or megaanni (Ma).
National geographic earth history timeline
Dating of the geologic record
The geologic record is the strata (layers) of rock in the planet's crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it.
Geologic time is the timescale used to calculate dates in the planet's geologic history from its origin (currently estimated to have been some 4,600 million years ago) to the present day.
Radiometric dating measures the steady decay of radioactive eleme