Geological Timescales › Revision notes
Geological Timescales — Revision notes
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Quick recap
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Brain dump
Before you look at anything else, write down everything you can remember about this lesson: key words, facts, examples. Spelling doesn't matter. Then see which of the 21 key terms you remembered.
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Key terms
- Geological timescale
- The timeline of Earth's history, split into sections of very different lengths
- Eon
- The largest division of geological time, lasting hundreds of millions to billions of years
- Era
- A division of an eon, lasting tens to hundreds of millions of years
- Period
- A division of an era, lasting millions of years
- Epoch
- A slice of a period, lasting thousands to millions of years
- Fossil
- The remains of a living thing trapped in rock layers, recording Earth's history like a diary
- Hadean
- The first eon, a violent world of volcanoes and meteorites when the first crust formed
- Archean
- The eon when simple life like bacteria first appeared in the oceans
- Proterozoic
- The eon when oxygen built up in the air and the first life made of many cells appeared
- Precambrian
- The first three eons together, covering nearly 90% of Earth's history
- Phanerozoic
- Our current eon, starting about 540 million years ago; its name means visible life
- Paleozoic
- The first era of the Phanerozoic; its name means ancient life
- Mesozoic
- The middle era of the Phanerozoic, when dinosaurs ruled; its name means middle life
- Cenozoic
- Our current era, the age of mammals; its name means new life
- Trilobite
- An armoured sea animal of the Paleozoic, related to today's crabs and insects
- Pangaea
- One giant supercontinent formed when the land joined together
- Great Dying
- The extinction 252 million years ago, caused by huge volcanic eruptions, that ended the Paleozoic
- Mass extinction
- An event where a huge share of all species are wiped out
- Quaternary
- Our current period, the age of ice ages, which began 2.58 million years ago
- Holocene
- Our current epoch, which began around 11,700 years ago when the last ice age ended
- Anthropocene
- A proposed new epoch whose name means the human epoch
TERM — tap to reveal
What this lesson covers
How well do you know each one? Be honest: red means go back over it.
- Describe how Earth's 4.6-billion-year history fits onto a 24-hour clock
- Name the eon, era, period and epoch in order from biggest to smallest
- Explain why geologists draw the lines where the rocks show a huge change
- Outline the three eras of the Phanerozoic and the extinctions that end them
- Identify the eon, era, period and epoch we live in today
- Evaluate the argument for adding a new Anthropocene epoch
Test yourself
Cover the answer, say it out loud, then check the full quiz on the lesson page.
- Which is the largest division of geological time?
- Which of these is NOT an era?
- Which mass extinction wiped out the most species?
Topic quiz
21 questions on this topic only — not mixed with anything else, one at a time.
Question 1 of 21
Score: 0 out of 21
Spelling challenge
Read the definition, then type the correct spelling of the term. Uses the same terms as above.
Score: 0/0