Montessori History

Montessori History: Clock of Eras and Geologic Time Scale

This lesson introduces kids to the history of the Earth, from the time of its creation all the way up to the present. It is meant to be both impressionistic and humbling: to make children realize just how much time has passed and how much has happened on the Earth even before humans appeared.

Clock of Eras

The Clock of Eras is a quintessential Montessori lesson and it typically looks like this:

(Less the pteranodons, mammoths, and other organisms of course.)

The Hadean eon was named after Hades, the Greek God of the underworld, because the conditions on Earth at the time were hellish. The Earth had just formed, was still very hot, and frequently collided with other objects in the solar system.

During the Archean eon, the Earth’s crust had cooled enough to allow the formation of continents. It was during this eon that life on Earth began, although it was mostly limited to prokaryotes — simple single-celled organisms without a nucleus. Evidence of life during the Archean eon include the stromatolites found in sandstone in Western Australia. Stromatolites are layered rock formations that were formed by cyanobacteria.

By the Proterozoic eon, enough oxygen had accumulated in the Earth’s atmosphere. This led to the rise of advanced, single-celled eukaryotes — organisms whose cells have a nucleus — and eventually multi-cellular organisms.

The Hadean, Archean and Proterozoic eons are collectively called the Precambrian, meaning everything that happened in this history of the Earth before the start of the Cambrian period, which is the first period of the Paleozoic era, which is the first era of the Phanerozoic eon.

The Phanerozoic Eon is the geologic eon that we are on right now. Most of the living creatures — and even the extinct ones — that we know of today first appeared in the Phanerozoic eon and we talk about that in more detail in the Montessori Great Lesson: Coming of Life and Timeline of Life.

Geologic Time Scale

As mentioned above, the Clock of Eras is one of the traditional Montessori lessons and you can actually find several presentations of the Clock of Eras on YouTube, such as in this video. You may notice that some of those presentations and some of the older Montessori Clock of Eras materials — like those where the yellow section takes up virtually half of the clock — seem a bit outdated.

For this lesson, however, we use the geologic time spans set by the International Commission on Stratigraphy (ICS).

While it’s important to be faithful to Montessori tradition, it’s equally important for kids (and adults!) to realize that science evolves, new discoveries are being made all the time, and when it comes to scientific discussions, it’s best if we use the same terms so that we can be confident that we’re talking about the same things and we can make sure we’re all on the same page. Older Montessori materials use terms like “the archaic era” which is no longer scientifically accurate. Some Montessori albums further add that the archaic era is also called the proterozoic era, which is also incorrect. There is, however, an archean eon and a proterozoic eon, which refer to two different things. So, to make sure, that we are going to be using the best science available to us at present, we’re using the terms set by the ICS. You can see them in the geologic time scale below and in our worksheets.

Reminder: we go into the Paleozoic, Mesozoic, and Cenozoic eras into more detail in Montessori Great Lesson: Coming of Life and Timeline of Life.

In the worksheets below, we focus on the basic elements of the Clock of Eras / Geologic Time Scale.

Note on the Worksheets

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