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RSSTime Words: Era, Epoch, and Eon
Sports writers are fond of saying that the retirement of someone or other marks “the end of an era.”
What is an era? And is it different from an epoch? What about an eon?
All three words denote a period of time. All three have specialized meanings for geologists. Here are their most common meanings and connotations.
Both era and epoch denote measurement.
In the sports writer’s usage, an era is a period in the history of a sport. It is a time during which a particular player, manager, or feature may be seen to typify the sport: the Babe Ruth era, the Casey Stengel era, the era of steroid use.
In the historical sense, an era can be a period of time marked by a specific beginning date: the Roman era (beginning with the traditional founding date of 750 BCE.), the Christian era (beginning with the birth of Jesus of Nazareth, now believed to have been 4 BCE), or the Muslim era (beginning with Mohammed’s flight from Mecca to Medina in 622 CE).
An epoch, (not to be confused with epic), like an era, is a period of time. An epoch is longer than an era and can cover more than one lifetime. It is marked by some significant development or series of developments: the feudal epoch, the epoch of exploration.
An eon is a very long time indeed. It is the longest period of geological time. Geologists subdivide an eon into eras. A geological era is subdivided into periods, epochs, and stages.
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I’m a little confused. Since “An epoch is longer than an era”, how come “A geological era is subdivided into epochs”?
Hmmm, good questions indeed, let’s wait Maeve to clarify.
As I say above, ” All three [words] have specialized meanings for geologists.” Geologists have to have some system in order to talk about the immense units of time they deal with. In their system an era is longer than an epoch.
In non-geological usage an epoch is generally felt to be longer than an era because the epoch is seen to precede the era. The epoch marks the beginning of something significant to human beings, for example, the earliest use of fire for cooking.
Here’s how H.W.Fowler puts it:
An epoch is the date of an occurrence that starts things going under new conditions.
An era is the time during which the conditions started at an epoch continue.
Got it!
Thanks for the post!
Just one question.
I read/heard about the word, “aeon”. Is that just a different way of spelling “eon”? Or is it a different word all together?
Tim,
Aeon is the same word. It suggests an even longer period to me!
Aha! Thank you!
Got it. Thanks, Maeve!
Is there a deffinite amount of years associated with eon or is it different with whoever meashures with it?
Joe,
number of years in an eon — here’s definition 4 in OED:
. Geol. and Astr. One thousand million years.