The oldest fossiliferous rocks in Britain are found in North Wales. Cambria is the medieval Latin name for Wales, so these rocks were named Cambrian. When rocks older than the Cambrian were discovered, they were labelled Precambrian.
| Superion | Eon | mya | Life forms | ||
| Precambrian | Hadean | 4600 | Earth molten | ||
| Archaean | 4000 | stromatolites | |||
| Proterozoic | 2500 | eukaryotes | |||
| Eon | Era | Period | mya | Life forms | |
| Phanerozoic | Palaeozoic | Cambrian | 541 | invertebrates | |
| Ordovician | 485 | land plants | |||
| Silurian | 444 | jawed fish | |||
| Devonian | 419 | amphibians | |||
| Carboniferous | 359 | reptiles | |||
| Permian | 299 | seed plants | |||
| Mesozoic | Triassic | 252 | mammals | ||
| Jurassic | 201 | dinosaurs | |||
| Cretaceous | 145 | birds | |||
| Era | Period | Epoch | mya | Life forms | |
| Cenozoic | Neogene | Palaeocene | 66.0 | mammals | |
| Eocene | 56.0 | modern mammals | |||
| Oligocene | 33.9 | new mammals | |||
| Miocene | 23.0 | more mammals | |||
| Pliocene | 5.33 | hominids | |||
| Quaternary | Pleistocene | 2.58 | humans | ||
| Holocene | 0.012 | civilisation | |||
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