Evolution Timeline — Major Events
Goal: be able to put the major events of cosmic + biological evolution in roughly the right order, with the right order of magnitude for when.
We measure in mya = millions of years ago.
For comparison: 1 mya = 1,000,000 years ago. The universe is about 13,800 mya old. A human lifetime is 0.0001 mya. The numbers are absurd; that's normal.
Tolerance
The exam accepts ±10% for each answer (with a minimum tolerance of 1 mya for very recent events). So for the Cambrian explosion (540 mya), anything from about 486 to 594 is correct. For Homo sapiens (0.3 mya), the tolerance widens to at least ±1 because the science itself is fuzzy.
In other words: you don't need to memorize digits, you need the right order of magnitude.
The timeline
| Event | Approx. mya | Notes |
|---|---|---|
| Big Bang | 13800 | The universe begins. |
| Earth forms | 4540 | Solar system condenses; Earth is here. |
| First life (single cells) | 3700 | Earliest fossil evidence of microbes. |
| Cambrian explosion | 540 | Sudden bloom of complex animals. |
| First fish | 520 | Earliest vertebrates. |
| First land plants | 470 | Plants colonize land. |
| First dinosaurs | 230 | Triassic period. |
| First mammals | 210 | Tiny, shrew-like, alongside dinosaurs. |
| KT extinction | 66 | Asteroid; non-avian dinosaurs gone. |
| First hominids | 7 | Our ape-like ancestors split from chimps. |
| Homo sapiens | 0.3 | Anatomically modern humans. |
Memorize the order, then the magnitudes
If you only remember the order (not the numbers), you'll still get most questions right. The numbers are then about scale:
- Universe / Earth / first life: thousands of mya (the big numbers).
- Cambrian / first fish / land plants: hundreds of mya.
- Dinosaurs / mammals: hundreds of mya, but smaller — order of 200ish.
- KT extinction: tens of mya (66).
- Hominids / sapiens: single digits or less of mya.
Three buckets:
- Thousands of mya — origins of the universe and life.
- Hundreds of mya — origins of complex life.
- Tens or fewer mya — origins of us.
Common mistakes
- Confusing "first dinosaurs" (230 mya) with "KT extinction" (66 mya). These are 164 million years apart — the dinosaurs ran the planet for most of that time.
- Thinking mammals showed up after the dinosaurs died. They didn't — they coexisted, but stayed small until the dinosaurs were gone.
- Thinking Homo sapiens are "old" on this scale. We are extremely young (0.3 mya = 300,000 years).
Sanity-check the scale
If 4540 mya (Earth's age) was 1 hour ago, then:
- First life: ~11 minutes after the start.
- Cambrian explosion: ~52 minutes in.
- KT extinction: ~59 minutes in.
- Homo sapiens: the last 0.25 seconds.
That's the entire point of the timeline.