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Planet Earth's Timeline

· History

Our planet has had a very long history, approximately 4.5 billion years1, during which many interesting and important things happened. To make more sense of this very very long history, a time scale was developed which breaks up the different periods of earth's history into different chunks based on important events. This scale is called the Geologic Time Scale.

Learning the Geologic Time Scale has numerous benefits. For me, it provided me with high level context that made visits to Natural History and science museums much more interesting. I also wish I had learned this before reading books like Elizabeth Kolbert's Sixth Extinction and Peter Brannen's The Ends of The World, as it would have added a lot more meaning to all the things they talked about.

What is frustrating about this time scale, however, is that its different divisions of time are difficult to remember. Their names sound similar to one another, their spelling is a bit odd and long, and there are a lot of them to remember. In this blog post, I'll not only go over what they are but also share with you an easy to follow strategy for actually remembering them.

Eons, Eras, and Periods

Similar to how a year is made up of months, which in turn can be divided into weeks, days, and hours, eons are divided into eras which are in turn divided into periods, epochs, and ages. Unlike time where 1 week is always 7 days long, these divisions are not all equal in length.

broken image

For instance, the first eon, the Hadean Eon, lasted about 600 million years2 (0.6 billion) while the eon that followed it, the Archean Eon, lasted about 2 billion years3. The last 2 remaining eons are the Proterozoic and the Phanerozoic.

Memory technique to remember the Eras and Periods

"Please Pay My Children" can you help you remember the Eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic.

"Come Over Some Day, Maybe Play Poker. Three Jacks Can Take Queens" can help you remember the Periods: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary.

These sorts of mnemonics creates what is called an anchor in your brain which is particularly helpful for remembering things in order. Further, try to visualize these phrases in your mind (e.g. Someone paying children) to take advantage of your mind's powerful visual memory. In this article so far, you have learned 22 pieces of information (4 eons, 4 eras, 12 periods, and 2 mnemonic). Each piece of information, or data point, is stored in its own learning site in your brain. A learning site is a certain neural path, a string of neurons, that fires. Unless you already knew of these, these neural pathways are weak at the moment. But that's nothing to worry about if you do something about it. Just like a regular muscle that can be strengthened by going to the gym, these new neural patterns also need to be worked out or else they will disappear. Unlike a gym session, however, your memory workouts will have more lasting effects. After enough of them, these neural pathways will be permanently ingrained and although they may weaken slightly over time, you will never forget the information.

Strategy for remembering the Eons, Eras, and Periods

Based on the forgetting curve, a curve modeled by the scientist Hermann Ebbinghaus, and later validated by numerous studies, you will only remember about 30% of the content in this blog post by tomorrow. Due to the difficulty of the geologic names, you may end-up remembering even less. Thankfully, we can use our understanding of the forgetting curve to use it to our advantage. In order to remember the names of the eons you just learned, you can start moving them to your long term memory system by strengthening those neural pathways. This is best accomplished by using recall, which means you should test yourself rather than simply review the information by re-reading it. Try answering these following questions now:

How many eons are there?

What is the first eon?

What is the second eon?

What is the third eon?

What eon do we live in now?

Self-quizzing yourself is a simple yet powerful technique for remembering information. If you want to remember this information for the future, try answering these questions again twice today, once tomorrow, and once next week. This is critical, since the longer you wait between review sessions the more cemented the neural pathways become. You can add a reminder in your calendar or to-do list to ensure you will do it. Alternatively, sign-up to become a beta tester for our Sapienza learning application. The application is designed to test you at optimized intervals to help you commit the information you want to remember forever to your long term memory system. It takes care of scheduling the review questions for you so you don't have to, making it extremely easy and efficient to remember the things you are interested in forever. To get early access to the Sapienza app and become a beta tester, shoot us an email at