Download Chapter 22- The Precambrian Earth

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