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Definition of: geoid
(jē′oid) noun
The earth considered as an ellipsoidal solid whose surface coincides with the mean level of the ocean. [<Gk. geoidēs earthlike <gē earth + eidos form]
| ERAS | TIME PERIODS ROCK SYSTEMS | TIME EPOCHS ROCK SERIES | APPROX. DURATION MILLION YEARS | APPROX. PERCENT TOTAL AGE | LIFE FORMS |
| CENOZOIC | QUATERNARY | RECENT PLEISTOCENE | 1 | Rise and dominance of Man. | |
| UPPER TERTIARY | PLIOCENE MIOCENE | 2 | Modern animals and plants. | ||
| 65 | |||||
| LOWER TERTIARY | OLIGOCENE EOCENE PALEOCENE | Rapid development of modern mammals, insects, and plants. | |||
| MESOZOIC | UPPER CRETACEOUS | Primitive mammals; last dinosaurs; last ammonites. | |||
| 75 | |||||
| LOWER CRETACEOUS | Rise of flowering plants. | ||||
| JURASSIC | 45 | 5 | First birds, first mammals. Diversification of reptiles; climax of ammonites; coniferous trees. | ||
| TRIASSIC | 45 | Rise of dinosaurs; cycadlike plants; bony fishes. | |||
| PALEOZOIC | PERMIAN | 45 | Rise of reptiles. Modern insects. Last of many plant and animal groups. | ||
PENNSYLVANIAN | First reptiles. Amphibians; primitive insects; seed ferns; primitive conifers. | ||||
| CARBONIFEROUS | 75 | ||||
MLSSISSIPPIAN | Climax of shell–crushing sharks. Primitive ammonites. | ||||
| 9 | |||||
| DEVONIAN | 50 | First amphibians, first land snails. Primitive land plants. Climax of brachiopods. | |||
| SILURIAN | 20 | First traces of land life. Scorpions. First lungfishes. Widespread coral reefs. | |||
| ORDOVICIAN | 70 | First fish. Climax of trilobites. First appearance of many marine invertebrates. | |||
| CAMBRIAN | 50 | First marine invertebrates, including trilobites. | |||
| PROTEROZOIC | First signs of life. Algae. | ||||
| PRE-CAMBRIAN | About 3,000 | 84 | |||
| ARCHEOZOIC | |||||
| Age of oldest dated rocks: about 3,500,000,000 years. | |||||
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