Time Words: Era, Epoch, and Eon

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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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22 thoughts on “Time Words: Era, Epoch, and Eon”

  1. 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.

  2. 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?

  3. Uhmm..I thought Super eon is the longest unit of time in geologic time scale were as divided into two major Eon the precambrian and Cambrian..please correct me if what I know was incorrect

  4. Once again, Maeve presents contradictory and incorrect information in an article. Amazing how someone with so little actual knowledge of the English language can pretend to be such an authority.

    An epoch is NOT generally considered to be a longer period of time than an era.

    An epoch is a period of time that can be defined by an event, and can be as brief as the event itself. An era is a period of time between epochs. These are not the geological definitions, but the generally-accepted uses for everyday English.

  5. Breed7,
    If I have misdefined “epoch,” you are certainly right to call me on it. To imply that I habitually disseminate incorrect information without providing me with specific examples is less than helpful. I’d be grateful if you would send me a list of the articles that you feel contain contradictory and incorrect information. My email is maevemaddox-at-gmail.com/.

  6. An aeon is exactly 1,000,000,000 years, just as an epoch is a measure of time for a specific event. Such as the ‘Thirty Year War’, or when Queen Elizabeth rose to power. I think neither of you are incorrect, because both definitions coincide within the meaning of the word. It’s merely a subjective manner in which the writer chooses to use the word.

  7. Why has this article still not been revised? It is common knowledge that an Era is longer than an Epoch as an Epoch is a subdivision of an Era. You should clarify that an Epoch may, at times, exceed the length of an Era but generally speaking is not considered to.

  8. Era, Epoch, and Eon — Duh?
    Since Queen Elizabeth I was mentioned, her time is called “the Elizabethan Age”. We now lived in the second Elizabethan Age.
    There were the “Victorian Age”, and “The Age of the Dinosaurs”, too.
    Also, the “Era of the Pharaohs”, the “Epoch of the Mongol Khans”, the “Epoch of the Tsars”, and the “Era of the cave man”.
    I think that the usage is often idiomatic.
    “The Stone Age”, “The Bronze Age”, “The Iron Age”.
    You have also discounted (ignored) the possibility of exaggeration, e.g. “I had to wait for eons at the dentist’s office.”
    e.g. “It seemed like Franklin D. Roosevelt was the President for an eon.”
    “The Georgian Age”, which also included the reign of William IV, because he was surrounded by George I, George II, George III, and George IV.

  9. If you were to visualize it in events then here are the breakdowns….

    Age is determined by…well Age.
    Like… The introduction of gun powder led to the end of The Great Swiss Pikemen Era who were vicious mercenaries known to imperial civilizations in europe until the 16th Century or you could say Mongol Era destroyed and swept the whole eurasian and all of europe in the Feudal Age of mongol expansion.

    There’s also this word Saga…
    The Saga between Constantine vs Saladin took a long time battle and a lot of lives in the Age of the Roman Empire, it was for both faction, an Era for Religious Cause.
    The start of the Abrahamic religion was the Epoch in time for organized theocracy that flourished in kingdoms with a political nature of feudalism, imperialism and colonialism spanning from the Medieval Age to Pre-Industrial Age, that which then came the Revolutionary Era where major events changed such as political systems from kingship to peoples marching for independence through the scope of different style of governing in difference parts of the world, an Epoch in time where governing religions decline in most parts of the world.

    The beings of Earth living for Eons gradually becoming intelligent in using tools to create homes and families, most notably the Humans, who made civilizations from Nomadic Age to the current Information Age, there were Eras of war, famine and plague. This is the Epoch in time that revolves around trade and settlements.

    Some historical info maybe incorrect but thats how i can give example in sentence between era, epoch, eon and age. 🙂

  10. Jeremy, I think Dale was just trying to bring to our attention the needlessness of looking for a difference among the three words, as they can be used quite interchangeably, and also according to the writer’s disposition. For instance, the example “I had to wait for eons at the dentist’s office” is in agreement with no rule that may stipulate the correct number of years attributed to an eon. Just like the Bronze Age could easily be termed the Era of Bronze, etc, etc.

  11. So, is the term Pleistocene an Epoch or an Age? Also, what’s the difference between Pleistocene and Paleolithic as these two geochronological descriptions happened in roughly the same time?

  12. this was frustrating to read. as an avid student of chronostratigraphy, this article, which ranges from misleading to outright wrong on just about everything it touches, was a really painful slog to get through.

    I’m a really big critic of people who speak in the authoritative tone (as this author did) on a topic they have little more than a passing interest in. no specialized knowledge; just a glorified “opinion” at best.

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