Surely you know that phase of our childhood in which everything around us took us out a “why” and “what for?”. Not abandoning that intellectual interest is key to many aspects of life. And it serves us for this article in question. Why is the movie “Jurassic Park” called like that? Because the Jurassic was a period when there were dinosaurs. And why Jurassic? And continuing with that insatiable curiosity: where do those strange names that we study in geology come from?
A little below these lines we have added the chronological table of the history of the Earth . An authentic madness of names and colors that remind us of the bitter hours of class. But as teachers would say: you don’t have to memorize it, you “just” understand it. Well, what a consolation.
But since you have come here to learn of your own free will, you will surely want to know the reason for this table . Of course, we do not have space in this article to analyze everything, but it is necessary that we have an approach to the division of geological time . It would be necessary to start, in fact, from the very concept of “time”, but we will not do it. It is enough to know that to measure something intangible like time, geologists, paleontologists, historians and other disciplines divide time into parts. Furthermore, each culture and specialty has its own way of counting and measuring: “Before Christ” is meaningless to a Muslim.
It is important to know that the chronological table is constantly updated according to new discoveries and studies that change concepts and chronologies. The table presented here is the latest update available on the website of the International Commission on Stratigraphy . If you are reading this a few years after its publication, some data may have changed (we hope that future will go well, because this present is not going great). If so, you have the updated table available on the Commission’s website and it can be downloaded in any language. Let us see, then, some of these names and their origin. As Jack the Ripper would say: let’s go in parts.
The table is divided , spanning from more to fewer years, into eons, eras, periods, epochs, and ages . As we get closer to the present, we have more divisions and in shorter periods of time. In general (but not uniquely), the names come from the characteristics of the life forms or rock formations of each stage . They are terms that derive from classical languages, especially from Greek.
Aeon
It is the largest division of geologic time . In Greek it means “eternity”. You will see that in the table it is also called an eonotema. This refers to the chronostratigraphic unit (the rocks that formed at that time) and applies to the rest of the table.
We start with the pitfalls, and we have a supereron , but only one: the Precambrian . It is nothing more (or less) than an informal way of calling the entire stage before the Cambrian . Put like that, it sounds unimportant, but the Precambrian occupies three eons, which add up to more than 4 billion years, from the formation of the Earth to 540 million years ago. It is almost 90% of the history of our planet . You can breathe now, we have nothing left then.
Going back to the eons, we only have four: Hadean , Archean , Proterozoic , and Phanerozoic . The Hadean was coined in 1972 by the geologist Preston Cloud, in relation to Hades, the Greek underworld. Archaic is clear, it also comes from the Greek and means “beginning, “origin”. If zôon is “living being” in Greek, the Proterozoic refers to “primitive life” and the Phanerozoic to “visible life”.
It was
The dynamic is similar to the whole picture although there are more and more divisions with their bombastic names. We have ten eras , but they didn’t get too complicated with them. Although they also come from the Greek, their names go according to the temporal order and that’s it: Paleozoic (ancient life), Mesozoic (intermediate life) and Cenozoic (recent life). In the Precambrian you can see the remaining seven eras, but equally solved with “Paleo-“, “Meso-” and “Ceno-” for each division of the corresponding aeons.
Time course
Here we already begin to have a broader casuistry to explain where these names come from. Among the most curious are the Cambrian , as the geologist Adam Sedgwick identified this system in 1831 in Wales, which during Roman rule was called Cambria . The Carboniferous can be easy to guess. Although the term originated with William Conybeare and William Phillips, it refers to the formation of coal deposits around the planet during this period.
We finally arrived: why is the Jurassic called so? The first use of this term is attributed to the French zoologist Alexander Brongniart, around 1829, who worked with Georges Cuvier, the father of paleontology. The name comes from Mount Jura , in the Alps, where the characteristic rocks of the system were identified. The Jurassic was the middle period of the Mesozoic, the age of the dinosaurs and when the supercontinent Pangea began its separation.
The most current periods of the table have been modified and renamed several times . At the time of publishing this article, we have three periods in the Cenozoic: Paleogene (“old generation”), Neogene (“new generation”), and Quaternary (“consisting of four”). But if Quaternary is not divided into four parts! Geologists like to watch the world burn, yes. The Quaternary name was proposed in 1759 by Giovanni Arduino, because he saw four rock formations for this period. But the debate has been (and continues to be) long and intense. If you’re still there, reader of the future, tell us what the era in which you live is now called, perhaps they have changed the name again.
times and ages
Finally, we have so many times and ages to be here for weeks writing. The epochs have little mystery because you can see that they either have their own names or are divided into “inferior”, “middle” and “superior”. Ours, the Holocene , comes from joining the Greek words holos (“all”) and kainos (“recent”).
And as for the ages , their names come from all possible options: types of life, locations where discoveries were made, their relative positions (lower, higher) and there are those that are limited to a sad “floor 2”. You’re still in time to give some ages a cool name.
We can only notice the experimental game that compresses the history of the universe in a year . Each day would be 40 million years and our species would not appear until 23:59 and 46 seconds on December 31 . It is good to keep in mind our position in time now and in the future.
References:
Graciela Arguello. Locosporlageologia.com.ar.Gradstein, F. M. et all. 2020. Geologic Time Scale. Elsevier.International Commission on Stratigraphy. International Stratigraphic Chart. stratigraphy.org.
