The early Earth's atmosphere was primarily composed of gases like carbon dioxide, nitrogen, and ammonia. Oxygen was not a significant component and only became abundant later due to the photosynthetic activity of organisms.
List I | List II | ||
|---|---|---|---|
| A | Mesozoic Era | I | Lower invertebrates |
| B | Proterozoic Era | II | Fish & Amphibia |
| C | Cenozoic Era | III | Birds & Reptiles |
| D | Paleozoic Era | IV | Mammals |