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Transcript
Chapter 22The Precambrian Earth Early Earth The Age of Earth Earth is estimated to be 4.56 billion years old. Precambrian time accounts for 90% of Earth’s history, and is divided into THREE eons: Hadean – No signs of life Archean – Prokaryotic organisms Proterozoic – Eukaryotic organisms Evidence of Earth’s Age Crustal Rock – pg. 620 Solar System – pg. 621 Early Earth Early Earth’s Heat Sources – pgs. 621 & 622 Gravitational Contraction Radioactivity Bombardment Earth’s Cooling Took about 200 million years, for liquid water to form. Cooling continues to this day. Formation of the Crust & Continents Formation of the Crust Differentiation Earliest Crust High density elements sank toward the center. – Graph pg. 624 Resembled oceanic crust, and was recycled. None exists today. Continental Crust Reactions with the early crust and water, created less dense material, which led to microcontinents. Cratons were formed, the deepest parts of the crust… up to 200km thick. Precambrian Shields – Areas where cratons are exposed, In North America, we have the Canadian Shield. Formation of the Crust & Continents Growth of the Continents Mountain building Laurentia as microcontinents collided, mountains and mountain ranges were created. Ancient North America, was created by collisions 1.8-1.6 bya. Rodenia 1st supercontinent. Positioned at the equator, with Laurentia at the center, was composed of 75% of all the continental crust. Pangaea – 300 mya Laurasia & Gondwanaland – 200 mya Formation of the Atmosphere & Oceans Formation of the Atmosphere – read pg. 628 Outgassing Oxygen in the Atmosphere Volcanoes do not typically produce Oxygen, so how’d it get into our atmosphere? 1st Oxygen producers Volcanic eruptions released large amounts of water vapor, carbon dioxide and Nitrogen into the atmosphere. Cyanobacteria – use photosynthesis and produce Oxygen. These cyanobacteria clustered together by the billions and formed Stromatolites. Evidence in Rocks – Iron Oxide presence. Banded Iron Red Beds Importance of Oxygen Animal Respiration Ozone Layer Formation of the Crust & Continents Formation of the Oceans Where did the water come from? Outgassing Bombardment Earth cooled, liquid water formed, water cycle began… Rain! Oceans and rivers formed, minerals dissolved and made the new oceans salty. Water & Life Liquid water made it possible for life to exist on our planet. Early Life on Earth Origin of Life Primordial Soup Miller’s Hypothesis – 1953 Read pg.633,634 How Life Might have Begun on Earth… 3 Ideas. Copy table 22.1 Earth’s Surface Deep Earth Space RNA World – read pg.635 Early Life on Earth Proterozoic Life Precambrian was dominated by unicellular organisms TWO types: Prokaryotes – NO membrane bound nucleus, smaller. Eukaryotes – membrane bound nucleus, larger. Multicellular Organisms Present around 630 mya. Ediacaran biota