#epoch

Tottoko Hamtaro Figure Sets (I collect the epoch Hamtaro figures, consider this a wishlist lol)

Deep time is not an easy thing to try and comprehend and it certainly doesn’t help when there’s all these crazy names being thrown at you. Let’s take a moment to break it down and really understand what we are seeing. The largest unit of geochronologic time is an eon. There are four formally defined eons: the Hadean, the Archean, the Proterozoic, and the Phanerozoic. The Hadean Eon is the oldest eon going from 4.6-4 Ga years ago. Its name is derived from the Greek god, Hades in reference to the still molten surface of the newly formed planet.

Following the Hadean Eon is the Archean Eon. This eon went from 4-2.5 Ga years ago. As mentioned in my Barberton Greenstone Belt video two weeks ago, this eon saw the creation of oceans and mountains as well as the appearance of the first living organisms known as stromatolites which would put oxygen into the atmosphere. Archean means “beginning or origin” which is fitting.

Next came the Proterozoic Eon. Lasted from 2.5 Ga-545 Ma. During this eon, the atmosphere became oxygenated, there were several glaciations, and the first eukaryotes evolved represented by the Ediacaran Biota. The name Proterozoic means “before life” because initially, fossils hadn’t been found until the Cambrian Period.

The last eon which we are currently in is the Phanerozoic Eon. It means “visible life” which makes sense as most living organisms have existed within this eon.

Okay, eons make sense? Excellent. Eons are broken down into eras. Now the Hadean is not broken into eras simply because the only evidence of this eon are detrital zircons in Australia.

The Phanerozoic Eon is the current eon and most of you are probably familiar with its eras: The Paleozoic Era, the Mesozoic Era, and the Cenozoic Era. These names mean “old life”, “middle life”, and “new life” respectively.

Eras are then split into periods. Like the Hadean before it, there isn’t enough evidence to split the Archean eras into periods. Again, we will use the Phanerozoic eras to show the break down starting with the Paleozoic.

The Paleozoic Era is split into six periods: the Cambrian Period,

the Ordovician Period,

the Silurian Period,

the Devonian Period,

the Carboniferous Period

and the Permian Period.

These will be discussed in more detail later on down the road. I have already made posts on the Cambrian and the Ordovician Periods and this month is all about the Silurian Period.

The Mesozoic Era is split into three periods of which most people know the names: The Triassic,

the Jurassic,

and the Cretaceous Periods.

Each of these will be discussed in detail further down the road as well.

The Cenozoic Era is also split into three periods: The Paleogene Period,

the Neogene Period,

and the Quaternary Period.

These will also be discussed in detail later.

Periods are further broken down into epochs. There are no formal epochs outside of the Phanerozoic Eon. Some early Paleozoic periods also do no have formal epochs. Many such as the Triassic and Jurassic Period are split into Early, Middle and Late. Strangely, the Cretaceous is only split into Early and Late though I think an argument could me made to create a middle.

The most well-known epochs are those of the Cenozoic Era. The Paleogene Period is split into three epochs: the Paleocene Epoch meaning “old dawn”,

the Eocene Epoch meaning “dawn”,

and the Oligocene Epoch meaning “few new”.

The Neogene Period is split into two epochs: the Miocene Epoch meaning “less new”

and the Pliocene Epoch meaning “more new/recent”.

The Quaternary Period is split into two epochs as well: the Pleistocene Epoch meaning “most new/recent”

and the Holocene Epoch meaning “whole new” and is the epoch we are currently in.

Epochs can then be broken down into still smaller categories called ages. For example, the Late Jurassic Epoch is broken up into three ages: Oxfordian Age, Kimmeridgian Age and Tithonian Age.

Now let’s put all these, eons, eras, periods, epochs, and ages into perspective. Let’s pretend Earth’s current lifespan is a clock. At 12:00, the Earth’s crust forms (Hadean Eon). At 2:10, the oldest rocks are preserved (Archean Eon). At 3:17, the first bacteria appear (Proterozoic Eon). At 11:52, the Cambrian Explosion occurs. At 11:53, first plants and fish. 11:54, first insects. 11:55, first reptiles and amphibians. 11:56, Mesozoic Era begins. 11:57, first dinosaurs, mammals, and birds. 11:59 Cenozoic Era.

Need a different visual? Try a calendar. The Hadean starts in January and ends halfway through February where the Archean picks up. The Archean lasts until halfway through June. From there, the Proterozoic starts and doesn’t end until about Thanksgiving. The Paleozoic Era then goes until about a week before Christmas. The Mesozoic covers Christmas to the December 30. New Year’s Eve represents the Cenozoic Era.

Thanks for coming to this lesson and make sure to tune in tomorrow for some fun trivia! Fossilize you later!