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Earth’s History 4 Eras of Geologic Time 4 Eras of Geologic Time Precambrian Paleozoic Mesozoic Cenozoic Precambrian Events The earth’s crust formed The atmosphere formed The ocean’s formed First life forms developed The earth’s crust The earth was very hot from its formation (The nebular theory) It cooled from the outside As it cooled, the earth’s crust formed and cracked to form plates An atmosphere developed Volcanic activity was very common as the crust formed and cracked – CO2 and Nitrogen – H20 vapor – Methane, ammonia, and sulfur dioxides Earth’s atmosphere Earth has an atmosphere for 3 reasons 1. Volcanic history 2. Mass of the planet 3. Amount of radiation from the sun The oceans formed As the earth continued to cool, the water vapor in the atmosphere condensed and fell as rain. This water formed the oceans, rivers, lakes, streams, and underground water ways. What were the conditions on the early earth? Intense volcanic activity Warm, shallow seas Turbulent atmosphere – Lots of lightning – Lots of storms How did life form on this planet? Life originated on this planet Life was seeded here by – A comet carrying carbon compounds – An asteroid carrying single-celled life forms What did the first organisms on earth look like? The oldest fossils of life on this planet are – Bacteria – Blue Green algae Bacteria Single-celled life forms No true nucleus or organelles (prokaryotes) Very hardy and resistant to extreme conditions Many species do not need oxygen Blue Green Algae Single celled organisms Prokaryotes Able to photosynthesize—use CO2 and H2O to produce glucose (food) and O2 Put tons of oxygen into atmosphere Oxygen in the atmosphere Toxic to many forms of bacteria Changed our atmospheric makeup by adding ozone to the earth’s atmospheric makeup O2 is converted to O3 (ozone) by lightning What happens to early life forms? In order to survive they must adapt to using oxygen Single-celled organisms that have welldefined nuclei develop (eukaryotes) Multicellular algal forms develop (first plants) Paleozoic—Age of Fishes “Paleo”—means early and –”zoic” means animals Life “exploded” on the planet Many marine life forms developed Plants and animals move onto land – Small wetlands plants and simple insects Amphibians developed Atlantic ocean begins to develop and continents begin to move apart Mesozoic—Age of Reptiles “Meso” means middle “-zoic” means animals All continents joined together at the beginning of this era, but begins to break apart Animals—dinosaurs evolve and become extinct Plants—ferns the predominant plant form—flowering plants evolve Cenozoic—Age of Mammals “Ceno” means recent “-zoic” means animals Mammals evolve and flourish Humans and human civilizations develop