Last week we talked about what fossils are, but to really place them in history, it's probably a good idea to get a grasp of the different time frames. We can divide Earth’s history into huge chunks of time called eras, and it helps to imagine the earth as a many layered cake made up of these time periods.
Here’s the quick rundown:
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Precambrian (4.5 billion – 541 million years ago) – The earth forms from chunks of space rock, and ushers in life’s warm-up phase. Microbes, stromatolites, and nature's earliest experiments in complex life get going.
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Paleozoic (541 – 252 million years ago) – Trilobites scuttle around, giant ferns rise up, and the first fish, insects, and reptiles appear. Ends with the biggest mass extinction in Earth’s history (yup, bigger than the Dino killer).
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Mesozoic (252 – 66 million years ago) – The Age of Reptiles (and lets face it, probably the coolest era!) Dinosaurs rule the land, flying pterosaurs own the skies, and marine reptiles dominate the seas. Ends rather dramatically with the earth shattering impact and subsequent environmental fallout that wiped out T.Rex and friends!
- Cenozoic (66 million years ago – today) – The Age of Mammals. With dinos gone, mammals diversify, birds take over the skies, and eventually humans appear (and then start digging all of this up and writing weekly info posts about it all for you to read on your phones!)
Each of these eras is further divided into periods, which is where the more familiar names come from. The Paleozoic closes with the Permian, the Mesozoic is split into the famous trio of Triassic, Jurassic, and Cretaceous, and the Cenozoic has its own chapters too. These sub-divisions help scientists be more precise about when certain creatures lived, and when they died out.
This week’s sketch shows a cutaway of Earth’s layers, with these eras stacked like a time-layered cake. You can use this as a 'time map' to help place the fossils we're looking at when I throw out names like 'carboniferous' or 'Devonian'
Fun fact: If you compressed Earth’s entire 4.5 billion year history into a single 24-hour day, dinosaurs wouldn’t show up until about 10:45pm, and humans wouldn’t appear until 11:59pm!
