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Earth was formed 4.6 billion years ago.
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Earth cooled and solid rocks formed on its surface.
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Earth's surface cooled enough for water to remain a liquid, and oceans covered much of the surface.
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Photosynthetic bacteria began to pump oxygen.
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Vendian period. Life first began.
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Many vertebrates and invertebrates lived during this time. Cambrian period: 544-505 millions of yrs ago. Invertebrates, brachiopods, trilobites. Ordovician period: 505-440 millions of yrs ago. Silurian period: 440-410 million of yrs ago. Arthropods became 1st land animals. First vertebrates appeared. First land plants evolved from aquatic ancestors. Carboniferous period: 360-290 millions of yrs ago. Devonian period: 410-360 millions of yrs ago. Permian period: 290-245 millions of yrs ago.
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Some plants adapted to drier areas and invaded more habitats. Insects appeared on land. Most fishes had jaws, bony skeletons, and scales.
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Dinosaurs lived during this time. Mammals began to evolve during this era. Triassic period: 245-208 millions of years ago. Jurassic period: 208-145 millions of years ago. Cretaceous period: 145-65 millions of years ago.
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Mammals became common during the Cenozoic. Tertiary period: 65-1.8 millions of years ago. Quaternary period: 1.8-present
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Triassic: fishes, insects, reptiles, and cone-bearing plants. Jurassic: Birds. Cretaceous: Reptiles, birds, turtles, crocodiles, fishes, and marine invertebrates. Leafy trees, shrubs, and small flowering plants.
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Tertiary: climate was warm and mild. Marine mammals; whales and dolphins evolved. Grasses evolved, providing food for grazing mammals.Some mammals became very large, as did some birds. Quaternary Period: Earth’s climate cooled, causing a series of ice ages. About 20,000 years ago, Earth’s climate began to warm and sea levels began to rise. In the oceans, algae, coral, mollusks, fishes, and mammals thrived.Insects, birds, and land mammals were common
