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EARTH’S HISTORY NOTES Origin of Planet Earth Scientists believe the Earth and the other planets formed while the Sun condensed from a nebula Formation of Earth’s layered structure As Earth formed High-velocity impacts caused Earth’s temps to increase Iron and nickel sinks towards the core Less dense masses of molten rock produced primitive crust A early atmosphere was made mostly of CO2 Life evolves Earth Cools and oceans form Bacteria evolve 3.7 BYA Cyanobacteria produce oxygen for billions of years! CO2 in the atmosphere is almost completely removed and the amount of oxygen rises. Geologic Time Scale is a “calendar” of Earth history that divides geologic history into units •Originally created using relative dates Eon– the largest expanses of time Era – subdivision of an eon Periods – Subdivisions of eras Epochs – are the smallest timespans (not to be confused with ewolks!) Precambrian era (4.5 BYA - 540 MYA) 88% of Earth's history Precambrian rocks contain extensive iron ore deposits but no fossil fuels and few fossils • (Stromatolites Appear 2 BYA) Paleozoic era (540248 MYA) Often called the time of fish although true fish developed late in this period. First life forms Multi-cellular life forms with hard parts formed abundant Paleozoic fossils. Paleozoic era In the Early Paleozoic life was restricted to seas, invertebrates such as • Trilobites • Brachiopods • Cephalopods First organisms with hard parts, such as shells - perhaps for protection Late Paleozoic era Supercontinent of Pangaea forms causing dramatic climate shift Late Paleozoic First land plants grow extensive swamps forming coal Insects invade the land Fishes evolve into two groups of bony fish • Lung fish • Lobe-finned fish which evolve into the 1st amphibians Amphibians diversify Paleozoic is believed to end as a result of enormous volcanic eruptions in what is now Russia. These events poisoned the sea and air and lead to the extinction of 95% of species! Mesozoic era (248-65 MYA) Survivors of the great Paleozoic extinction evolve and diversity. Gymnosperms (Conifers and ferns) become the dominant tree Often called the "age of dinosaurs" Divided into the Triassic, Jurassic and Cretaceous Periods Seas invade western North America Mesozoic era Mesozoic life Divided into the Triassic, Jurassic and Cretaceous Periods Reptiles - first truly terrestrial animals readily adapt to the dry Mesozoic climate with shell-covered eggs that can be laid on the land. Mammals exist only as small rodent like creatures. Mesozoic era Dinosaurs dominate One group of reptiles led to the birds Many reptile groups, along with many other animal groups, become extinct at the close of the Mesozoic Most likely the result of a large asteroid or comet struck Earth The Chicxulub Impact Site Cenozoic era (65 MYA-Present) Shortest era of geologic time Mammals diversify & replace reptiles as the dominant land animal some groups become very large (Hornless rhinoceros, stood 16 feet high!) Angiosperms - flowering plants dominate the plant world • Strongly influenced the evolution of both birds and mammals • Provide a food source for both birds and mammals Cenozoic era Human Species Evolves 2.5 millions years ago Homo habilis – early toolmaker 200 thousand years ago – Homo sapiens 50 thousand years ago modern humans and large animals go extinct 12 thousand years ago development of agriculture and first cities 250 Million years in a snapshot