Cretaceous, Holocene, Mesozoic, Cambrian, Phanerozoic ... What the *bananas* do all these words mean?
These preposterously fancy, enigmatic sounding words describe long time periods in Earth's history. Commonly, these time periods are refered to as "eras". But, geologically speaking, this isn't entirely correct. Let's have a closer look.
Welcome to the SCIENCE OF TRAVEL Blog! I'm Daniela, a geoscientist (B.Sc.) and passionate about Earth, landscape formation, respectful traveling and philosophical thoughts.
In this article you'll find out:
- How the geologic time scale is structured
- What deep time is
- What era we live in
- What era the dinosaurs lived in
- What the time scale has got to do with you
- Where you can learn more about Earth's history
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The Geologic Time Scale
Earth is 4.56 billion years old. Geoscientists divide its complete lifetime into smaller chunks: eons, eras, periods and epochs.
Eons are subdivided into eras, these into periods, these into epochs.
All combined make up the geologic time scale. This is a chronologic table that expresses the entire history of the Earth on the basis of rock layers.
I created this simplified overview of a so-called stratigraphic chart that lists all time periods. You can also see from when to when a specific period was. The column on the very right tells you how long in total a specific period lasted.
In the following, I name the units within each division in descending age, so the first mentioned is the oldest!
The first division are eons. Depending on the definition, there are 2 or 4 eons.If we go with two, there are the Pre-Cambrian and the Phanerozoic. The Pre-Cambrian is older than the Phanerozoic. If we go with four eons, there are the Hadean, Archean, Proterozoic, and Phanerozoic. The Hadean is the oldest, the Phanerozoic is the youngest.
The Phanerozoic, the most recent eon, has three eras which represent the second division. These eras are the Paleozoic, the Mesozoic, and the Cenozoic.
Each of these eras is divided into periods. Periods are the third division. Each of these periods is, give or take, 50 million years long. In total, the Phanerozoic eon has 12 periods, here listed from oldest to youngest. The first period of the Phanerozoic is the Cambrian, then comes the Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene and Quaternary.
The part of gesciences that deals with the geologic time scale, examines and describes the rock layers and their relationship is called stratigraphy. "Stratum" is Greek and means "layer". "Graphia" is Greek and means "write; describe". Stratigraphy is the part of the geosciences that describes rock layers.
The transition from one unit to the other goes along with major changes or events in Earth's history. These could be: the emergence of life, the emergence and disappreance of a species, extinction events and changes in environmental conditions or compositions of fauna (wildlife) and flora. Fossils are important indicators for specific rock layers.
Just to give you an example, the extinction event that took place 66 million years ago that, famously, caused the extinction of many species including the dinosaurs marks the transition from the Cretaceous period to the Paleogene period. This is also the transition from the Mesozoic to the Cenozoic era.
The geologic time scale is a neat system that makes sense. Not at first glance, perhaps not at the second or third, but with time and deeper knowledge.
The online program MENTOR EARTH has an entire chapter dedicated to deep time and the history of the Earth.
Deep time is a phrase that, basically, describes the long timespans of Earth and the universe that the human brain isn't capable of understanding.
What era do we live in?
Answering this question geologically correct, the answer is: We live in the Cenozoic era.
But let's start with the first division, the eon. We live in the Phanerozoic eon. We live in the Cenozoic era within the Phanerozoic eon. The period within the Cenozoic that we live in is the Quaternary. The epoch within the period that we live in is the Holocene.
To recap:
| Eon | Phanerozoic |
| Era | Cenozoic |
| Period | Quaternary |
| Epoch | Holocene |
What era did the dinosaurs live in?
Answering this question geologically correct, the answer is: Dinosaurs lived in the Mesozoic era. They emerged in the late Triassic period, thrived in and dominated the Jurassic and Cretaceous periods, and died out atthe end of the Cretaceous period.
| Eon | Phanerozoic |
| Era | Mesozoic |
| Period | Triassic - Cretaceous |
What does the geologic time scale have to do with you?
Besides being incredibly interesting, it has everything to do with you.
Everything. This is the story of the planet you live on. It's humanity's cradle. It's your cradle. It's your home, the ONLY home you will EVER have. Ever. You won't live on Mars. Neither will your children nor their children. Earth deserves to be studied and honored and understood.
Understanding your place on this planet, its history and its workings, is crucial to our survival, I think. Understanding Earth's history, knowing its age, makes us realize that we aren't the center of the universe, not of our planetary system, and not even the center on Earth.
What do these facts evoke in you?
Learn more about the philosophical concept of Deep Time in the online program MENTOR EARTH.
Continue to learn about Earth
If you like this combination of geoscience and philosophy, then the program MENTOR EARTH is for you.
The course tells the complete story of Earth's history,explains its structure and dynamics and combines this knowledge with philosophical insights. You'll use the CORE TO CRUST template, that I invented, to structure your inner world.
Thanks for being here! Check out the course here.
Bye
Daniela
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About the author
 | Daniela is convinced that by gaining deep insights into planet Earth and travel destinations you’ll create meaningful, grounding and memorable life and travel experiences. She explains fundamental geological processes that form and shape landscapes and combines these insights with philosophical and philanthropical views in her online courses, articles, and newsletter. She holds two bachelor's degrees in geosciences (B.Sc.) and business administration with tourism (B.A.). She is the owner and founder of EarthyMe, EarthyUniversity and the Science of Travel blog and theSTORIES OF EARTHnewsletter. |
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Credits
Blog post banner: Photo by Andreas Gücklhorn.Lake Brienz, Switzerland.
Simplified geologic time scale: Daniela Dägele
