Geologic Past Foundations of Social Studies History

Geologic Time Scale  Definition: a system of chronological measurements based on the study of the/our planets rock layers.  According to the rock layers, Earth was formed about 4.5 billion years ago from dust and gas left over from the formation of the sun.  Initially earth was just liquid rock, the outer layer cooled to form a solid crust.  Water vapor accumulated in the atmosphere, it condensed, and along with ice delivered from comets and then they produced the oceans.

Geologic Eras  Earth’s life divided into enormously long time periods… Bonus Question: What do we call this??  Based on changes in the earth’s crust.  Fossils that appear in rocks help define the eras too.

Precambrian Era  Earliest and longest era  Takes the Earth from its molten state to a solid  Fossils indicate multi-celled animals from this era

Paleozoic Era  Early in the Era continents are far apart, then drifted into one continent Pangea  Ice covered to Northern Africa  Large numbers of vertebrates and invertebrates in the ocean  Also largest mass extinction

Mesozoic Era  Beginning of land animals and plants  Seed producing plants  Dinosaurs herbivores and carnivores  First mammals and birds  Dinosaurs ended when a meteor hit Earth

Cenozoic Era  Mammals are the predominant species  Diverse mammals, moved and began eating foods the dinosaurs ate  Grasses and grazing animals evolved  Human like creatures evolved called hominids

Pleistocene Epoch: The Ice Ages  End of the Cenozoic Era  The most recent episode of global cooling Earth warmed and receded four different time  Plant and animal life similar to modern times and many still survive today  Large animals, for example the Mammoth, lived in early part of the era then became extinct.  Expansion of our species homo-sapiens  These humans did not survive perhaps because of disease

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