Geological Time Scale
Earth's 4.6 billion year history is divided into eras.
About this topic
Earth is about 4.6 billion years old. The geological time scale divides this into eons (Hadean, Archean, Proterozoic, Phanerozoic), eras (Paleozoic, Mesozoic, Cenozoic), and periods like the Cambrian, Jurassic and Quaternary, bounded by major events such as mass extinctions.
If Earth's history were a 24-hour day, life appears around 4 am, animals around 9 pm, dinosaurs at about 10:40 pm, and humans in the last minute. The scale helps put evolution and change into context.
The time scale is like a calendar for the planet, with names given to units marked by rock and fossil changes. The Cambrian explosion, about 540 million years ago, saw a rapid diversification of animals with hard parts. The Permian extinction, about 252 million years ago, was the worst, wiping out around 90 percent of marine species, and the Cretaceous event at 66 million years ago ended the non-bird dinosaurs. The Phanerozoic ('visible life') covers just the last 12 percent of Earth's history.
Geologists used relative dating and fossils to build the scale in the 1800s and later added radiometric ages. Knowing it helps in finding fossil fuels, understanding past climate and seeing that extinction and change are normal, though today's rate is high. The current proposal of the Anthropocene recognises human impact on the geological record. A misconception is that humans and dinosaurs lived together; non-bird dinosaurs died out about 66 million years ago, while modern humans appeared around 300,000 years ago. Another is thinking that deep time is just a big number; use scaled analogies to grasp it.
Key ideas
- Precambrian, Paleozoic, Mesozoic, Cenozoic
- Mass extinctions mark boundaries
- Humans are very recent
Quick check
Use cases: where Geological Time Scale helps
- Homework: review the key idea behind Geological Time Scale before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Geological Time Scale without notes.
- Visual learning: play with the interactive lab to see how Geological Time Scale changes when you adjust its inputs.
- Teaching a friend: explain Geological Time Scale in your own words, then compare your version with the key ideas.
Earth science helps with weather forecasts, natural hazards, energy and climate planning.
Frequently asked questions
What is Geological Time Scale?
Earth's 4.6 billion year history is divided into eras.
What will I learn in Geological Time Scale?
Precambrian, Paleozoic, Mesozoic, Cenozoic. Mass extinctions mark boundaries. Humans are very recent.
Is Geological Time Scale part of Earth & Space?
Yes. It is one of 60 Earth & Space topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Geological Time Scale lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Geological Time Scale?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.