What you'll learn from these flashcards
How Earth's geological history is organized into eons, eras and periods, and what distinguishes these divisions.
You'll trace the major milestones: from the formation of the young planet and the earliest life to life moving onto land, the age of dinosaurs and the appearance of humans.
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More about the collection's contents
Geological Eras and Periods of Earth
Earth's geological history spans roughly 4.6 billion years. Scientists divide it into four eons: Hadean, Archean, Proterozoic and Phanerozoic. The first three account for about 88% of Earth's history. The Phanerozoic, which began around 539 million years ago, occupies only the remaining 12%.
- Hadean11.7%
- Archean33.5%
- Proterozoic42.9%
- Phanerozoic11.8%
The boundaries of geological divisions are established from changes preserved in rocks. Rock layers and fossils reveal the relative order of events, while radiometric dating helps determine the ages of rocks.
The Phanerozoic fossil record is particularly rich in organisms with hard body parts, so its periods are especially well studied. But the Proterozoic has ten recognized periods too, and our timeline includes all of them. No official periods are defined for the Archean or Hadean.
Earth's history on a timeline
Eons are divided into eras, and eras into periods where those divisions are formally defined.
Formation of the young Earth
No official eras or periods are defined.
Formation of early Earth's crust
Development of microbial life
Development of microbial life
Development of microbial life
No official periods are defined.
- Siderian2500–2300 Ma
- Rhyacian2300–2050 Ma
- Orosirian2050–1800 Ma
- Statherian1800–1600 Ma
- Calymmian1600–1400 Ma
- Ectasian1400–1200 Ma
- Stenian1200–1000 Ma
- Tonian1000–720 Ma
- Cryogenian720–635 Ma
- Ediacaran635–539 Ma
- Cambrian539–487 Ma
- Ordovician487–443 Ma
- Silurian443–420 Ma
- Devonian420–359 Ma
- Carboniferous359–299 Ma
- Permian299–252 Ma
- Triassic252–201 Ma
- Jurassic201–143 Ma
- Cretaceous143–66 Ma
- Paleogene66–23 Ma
- Neogene23–2.58 Ma
- Quaternary2.58 Ma — present
What the flashcards look like
This is a flashcard about the Devonian Period. The front shows the name of a geological interval. Try to remember when it happened and what Earth was like at that time. The Devonian is often called the “Age of Fishes”: fish became especially diverse, and the first vertebrates began moving onto land. If you don’t remember yet, turn the card over and discover this chapter of Earth’s history.
On the back you’ll find dates, a short explanation of major events and an illustration. The cards show when continents and mountains formed, how climates changed, when new groups of living things appeared and when mass extinctions occurred. Little by little, separate periods begin to fit into one larger story of our planet.
You don’t have to memorize the entire geological timescale at once. Start with the sequence of major divisions, then look more closely at individual periods and the events that define them. Revisit the cards that are still difficult, and Earth’s vast history will gradually become easier to understand.
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