WHAT UNIT OF TIME IS USED IN EONS AND GEOLOGICAL ERAS? - GEOGRAPHY - 2025

The units of time used in eons and geological ages correspond to a scale made up of three elements. These are: chronostratigraphic units, geochronological units and geochronometric units, each with specific criteria to quantify the duration of the periods.

This is done in order to develop a time map that groups different points of view, from the simplest, to those that allow greater precision.

While the chronostratigraphic units are based on soil studies, the geochronological ones have more variable perspectives.

As for geochronometric units, they are a form of expression of the first two.

How eons and geological eras are measured

For the purpose of establishing a reliable and easy-to-manage timeline, land history is often divided into stretches of time of immense duration, which are then broken down into shorter and more exact periods.

The use of geochronological units (eon, era, period, age) is common before chronostratigraphic units (eonothem, eratheme, system).

However, there is an equivalence between the two. The former were created thanks to arbitrary criteria usually associated with events or events of great importance, such as the emergence or extinction of species.

On the other hand, the chronostratigraphic units correspond to the divisions of the soil. By examining its content and characteristics, its age can be calculated.

Eon

It corresponds to the largest time division for the earth's timescale. It does not have a defined duration, although currently 4 eons are recognized from the emergence of the planet to the contemporary age.

- Hadic Aeon. Earth formation 4.5 billion years ago to 3.8 billion years ago.

- Archaic Aeon. From 3.8 billion years ago to 2.5 billion years ago.

- Proterozoic Aeon. From 2.5 billion to 540 million years ago.

-Eon Phanerozoic. From 540 million years ago to the present. It is from this eon that the first living organisms emerge beyond fungi and bacteria. This is when plant and animal life arises.

The first three eons are usually grouped into a supereon known as the Precambrian. This measure encompasses almost 90% of the duration of the earth's history.

It was geological

Ages are the second largest division of time for geologic timescale measurement.

They are the subdivisions that follow the eons, so they do not have a defined duration. Ten geological eras are recognized, these in turn are divided into periods.

Geological timescale

This scale serves as a reference to chronologically order the events and divisions that make up the history of the Earth. It is made up of 3 units.

Chronostratigraphic Units

Based on the variations of the fossil records, elements and characteristics found in the earth's crust. It is the most accurate unit for accurately measuring the geological ages of the earth.

Geochronological units

They are of arbitrary measures, although they have an equivalence with the chronostratigraphic units.

They measure stages of history depending on events that have been significant, for example mass extinctions, species emergence or ice ages.

Geochronometric units

Quantification of the 2 previous units, expressed in millions of years.

References

1. The Geologic Time Scale in Historical Perspective (nd). Retrieved on October 8, 2017, from the University of California.
2. Geologic Time Scale (sf). Retrieved on October 8, 2017, from Geology.
3. Geologic Time Scale (November 2012). Retrieved on October 8, 2017, from The Geological Society of America.
4. Andrew Alden (February 28, 20127). Geologic Time Scale: Eons, Eras and Periods. Retrieved on October 8, 2017, from ThoughtCo.
5. Geological scale (2011). Retrieved on October 8, 2017, from Infogeology.