what is the definition of eon?

eon is a unit of measurement for extremely long spans of geological time. In geology, an eon is the longest period of geological time, usually lasting about one billion years. It is larger than an era, which is typically hundreds of millions of years long. Geologists use eons to measure the age of the Earth and its geological history.

Eons are divided into eras, which are much shorter spans of time lasting tens or hundreds of millions of years. Each era is further divided into periods, epochs, and ages, which are all smaller units of time. For example, the Phanerozoic eon, which began 541 million years ago, is divided into the Paleozoic, Mesozoic, and Cenozoic eras.

Eons are not calendar-based, in that they measure geological time rather than human-defined months, years, and decades. Still, they can be represented on a timeline and compared to periods known to humans, such as the Industrial Revolution, which spanned the years from 1760 to 1840.

how long does an eon last?

When it comes to measuring the immense amount of time created by the universe, the eon stands out as the longest quantifiable unit. An eon is an immeasurable unit of time, as we as humans are unable to accurately measure its length. But even though an eon's exact length is impossible to determine, it is possible to estimate that it lasts around one billion to one trillion years.

Eons are key components in the Geologic Time Scale, which spans from the Earth's creation to its current timeline. Scientists divide the eon into two distinct periods known as the Precambrian and Phanerozoic. The Former is plotted out in two different eras known as the Archean and Proterozoic, which happened between 4.6 billion and 540 million years ago. During this time, the Earth began to experience its first living creatures, drastic changes in the environment, and its first steps towards the modern era.

The Phanerozoic period began 541 million years ago and is characterized by an intensive process of evolution, leading to a greater abundance of lifeforms ranging from plants, insects, and mammals. This period is divided into three distinct eras known as Paleozoic, Mesozoic, and Cenozoic. While these periods are much shorter than an eon, the lifeforms created and evolved during them are crucial to the existence of modern life as we know it today.

Despite its immense size, scientists do not estimate an eon to last forever. This is why the Geologic Time Scale stops at the Phanerozoic period and does not extend beyond it. It is also why when scientists cite a date, they (usually) approximate it to be limited between two finite points in time.