Chapter 11 Earth History

11-1    Origin of the Earth:

• Nebular hypothesis: cloud of dusts and gases contracted and spun ==> dish or disk-like nebular, center mass accumulate ==> protosun.

• Other local clouds contract the same way ==> protoplanets.

• Heavy elements under gravitational force formed in inner part of solar system. Outer planets lighter due to gases.

• Heating process was due to fusion of H₂ in the Sun.

• On the Earth, redioactive decay produced heat that can cause partial melting.

• Due to gravitational force, heavy elements accumulated in core and gas escape from the surface.

11-2    Atmosphere evolution:

• Compared to what comes off from a volcano, gas escaped from rocks when they cooled.

• Typical gases: CO₂, H₂O, N₂, etc. No O₂. Therefore, everything is in reduced environment.

• Water vapor condensed to form water.

• Lowland filled to form ocean.

• Anaerobic bacteria form.

• Primitive planets form, produce O₂ from photosynthesis.

• O₂ + Fe ==> Fe₂O₃.

• O₂ accumulated after all free Fe on surface converted to Fe₂O₃.

11-3    Precambrian: 

• 4.6 Ba to 570 Ma. Difficult to study due to lack of evidence, e.g. fossils and most of the rocks deformed.

1. Precambrian rocks: 

   • Where: underneath the younger strata, in core of continents, called shields.

   • Importance: rich in mineral resources, e.g. Fe, and Ni. Iron ore in mid Precambrian indicated free O₂.

   • Lack: fossil fuels indicating no major live involved.

2. Precambrian  life: 

   • Old saying: no life before Precambrian .

   • Now say that life does exist, but in a simple form.

   • Stramatolite: fossils produced by algae, similar to today's blue algae.

   • Initial produced asexually, e.g. prokaryotes.

   • Eukaryotes contain nuclei produced sexually.

   • Animal fossils rare, mostly trace fossils showing their activity. Because: animals nor hard shells.

11-4    Paleozoic:

Span: 345 Ma, covers 7 periods.

1. Early Paleozoic: Cambrian , O, S.

   • Landmass: Gondwanaland: South Africa, Antarctica, India, South America. Not Gondwanaland: North America and Europe.

   • North America: No mountains, low land. See invaded and make deposits in Cambrian  and O. 

   • Orogeny: Taconic. Appalachians formed end of O.

   • Evaporite bed in S.

   • Life: Trilobite: Cambrian - S. Brachiopods: O. Cephalopods: O. *** Hard shell exists.

2. Late Paleozoic: D, C (Ms, Pa), P.

   • Landmass: First Laurasia formed by fusion of North America and Europe, then Pangaea formed.

   • North America.

   • Orogeny: Urals formed. South Appalachian formed.

   • Life: 

     • Land plants start at D.

     • Fish appear at D.

     • Amphibian at C.

     • Larger trees in swamp to form coal.

     • Trilobite extinct at D.

11-5    Mesozoic:

Span: 180 Ma, covers 3 periods.

1. Landmass: breakup of Pangaea starts.

2. North America: In Tri, most land above sea level. Therefore, terrestial environment. J, K each with an invasion of sea.

3. Orogeny: Western North America formed. Rocky Mountains formed - Laramide Orogeny.

4. Life:

   • Plants: seed-bearing gymnosperms, e.g. conifers ginkoes.

   • Shell eggs: laid on land, no more dependent on water.

   • Dinosaurs dominate.

11-6    Cenozoic:

Span: 66 Ma, covers Ter and Q.

1. Landmass: Close to current setting.

2. North America: Above sea level. 

3. Eastern North America: 

   • Stable continental margins. 

   • Thick sediments.

   • Oil and gas accumulation at Gulf of Mexico. 

   • Rebound of Appalachian.

4. Western North America:

   • Basin and Range Provinces formed.

   • Rocky Mountains rehuvenated, e.g. Grand Canyon, etc.

   • Volcanic activity common.

   • Coastal Range formed

5. Life:

   • Mammals: replaced reptiles.

   • Flowering plants (angiosperms) dominant.

Homework:

• Read chapter summary on p.318.

• Use your own word to explain the key terms on page 319.

• Answer the review questions on page 320.