Time is what you make of it

I have a confession. My confession is slightly embarrassing considering that I work in the Earth Sciences: I don’t know my geologic timescales. When someone tells me a fossil is from the Ordovician or the Precambrian, I have no idea what they are talking about. Was that 10 million years ago? 167 million years ago? 1.92 billion years ago? 569 million years ago? I DON’T KNOW! There’s a reason why I went into Oceanography and not Paleontology – I can’t keep these ages straight. The worst part is that my students have to learn the geologic timescale in their general education class. So while they have everything memorized for midterms, I’m stuck with my finger up my nose trying to remember if the Pleistocene came before or after the Pliocene. That being said, why don’t we take today and learn the geologic timescale together? It’ll be fun!! You get to learn something new and I get to relearn the timescale for the 10th time and pray that my drinking binge this weekend won’t erase my memory. Again.


It would be fair to mention that I DO know some of these Eras and Periods. I know that the Cambrian was the time where all sorts of life appeared on our planet. The Cambrian Explosion was the explosion (!) of life in a very anticlimactic way. It was during this time that we find lots of fossil evidence of worms and sea-bugs and sponges and even more worms, but this time with teeth. Earth sounds like a pretty gross place back in the Cambrian, right?

So the Cambrian explosion occurred around 544 million years ago and I’m going to ignore (for now) the times before the Cambrian which are the Proterozoic, Archean, and Hadean. These 3 are Eras when the Earth was juuust forming. Most Paleontologists ignore these times in Earth history because it’s really really hard to find shit that’s 2-3 billion years old. The life that did exist were things like algae, bacteria, single celled organisms, viruses, and so on. Borrrring.

Moving on, the Cambrian/Precambrian boundary was around 544 million years ago, and then the next exciting thing was the Permian/Triassic boundary which was about 248 million years ago. An aside here: Paleontologists have a pretty clever way of defining the boundary between eras and periods. What they do is look at some sedimentary rock formation that’s got fossils in it, start at the bottom of the formation (where the oldest fossils live), work their way up to the top of the formation (where the youngest fossils live), and wherever older fossilized critters disappear they go “Aha! There must have been some cataclysmic event around this time that wiped out most life on Earth and allowed all these new critters to take over!” I don’t exactly know where they get the numbers from – must be by age dating rocks within the formation using some radioactive isotope. Reason # 122 why I'm not a Paleontologist.

We’ve covered the Boring Era (Precambrian), and then the Gross Period (Cambrian), and then we get into more exciting Eras and Periods like everyone’s favorite the Triassic and Jurassic (248 mya and 206 mya, respectively). Maybe at this point we should create a mnemonic device to help us remember most of these. If we can’t get the dates right, we can at least get the order right. Starting from the oldest first...

A…………………..Archean
Pizza……………….Proterozoic
Comes……………..Cambrian
On………………….Ordovician
Sunday,…………….Silurian
Delicious!..................Devonian

My…………………Mississippian
Pizza……………….Pennsylvanian
Precludes………….Permian
The…………………Triassic
Jaggoff………………Jurassic
Competition.…….Cretaceous

Put…………………Paleocene
Everything…………Eocene
On………………….Oligocene
My…………………Miocene
Pizza……………….Pliocene
Please, …………….Pleistocene
Harold…………….Holocene

Uh, well. That's a start. You know what? I'm just going to keep this chart handy in case I'm in a life threatening situation where I need to know when the Pennsylvanian was EXACTLY. Yes, that sounds like a good plan.

Happy Friday!