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Precambrian Time
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Early in Paleozoic Era, there was a diversity of marine life.
CAMBRIAN PERIOD: many organisms had hard parts.
ORDOVICIAN AND SILURIAN PERIODS: Ancestors of modern octopi and squid appeared. Aquatic anthropods also appeared. Among first vertebras where jawless fishes. First land plants also evolved, and lived in damp areas.
DEVONIAN PERIOD: Vertebrates began to invade land. First amphibians.
CARBONIFEROUS AND PERMIAN PERIODS: Reptiles evolved from amphibians, winged insects evolved. Remains of ancient plants formed thick deposits of sediment that changed into coal.
At end of Paleozoic Era, there was a mass extinction. As much as 95% of complex life in oceans disappeared.
Marked by appearance of flowering plants, and by dominance of dinosaurs.
TRIASSIC PERIOD: Organs that survived the mass extinction became the main forms of life. Reptiles were very common, and this is often known as "age of reptiles". Mammals very small in this time.
About 225 million years ago, first dinosaurs appeared.
JURASSIC PERIOD: Dinosaurs became dominant. They ruled the Earth for about 150 million years. First birds appeared during this time.
CRETACEOUS PERIOD: Reptiles were still dominant during this period, but the flying dinosaurs became extinct during this period.
At end of this period, another mass extinction occurred, and more than half of all plant and animal groups were wiped out, including dinosaurs.
During this era, mammals evolved adaptations that allowed them to live in various environments. Cenozoic Era is called "Age of Mammals".
TERTIARY PERIOD: Earth's climates are generally warm and mild. Dolphins/whales evolved. Grasses also evolved. Grazing mammals (ancestors of cattle, sheep, deer, etc.) appeared.
QUATERNARY PERIOD: Cool environment, caused a series of ice ages. Then around 200,000 years ago, Earth's climate began to warm, causing sea levels to rise again.
**Fossil record suggests that early ancestors of our spices started around 4.5 million years ago, but did not look entirely human.