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The Earth Through Geologic Time

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Is the Present ALWAYS the Key to the Past?

• Uniformitarianism– processes (physical, chemical, and biological) in the

geological past are similar to today

• Catastrophism– periodic catastrophic (high energy/short duration) events

dominate the geological record

• Punctuated Uniformitarianism– Short lived high magnitude events leave a comparable

record(in terms of the proportions of the geological record) compared to slow, persistent, low energy events.

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Important Episodic Events

• Earthquakes

• Volcanic eruptions

• Storms

• Jokulhlaups– Outburst floods in glacial terranes

• Submarine slumps

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Uniformity? of Physical, Chemical, and Biological Processes Through Earth History

• Biosphere changes– Carbonate Bioclasts

• Sediment particles a result of biological processes and organic evolution

– Changes in Vegetation– Atmosphere composition and Atmospheric

Circulation

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• Carbonate Sedimentation

– > 1 Ga• only cyanobacteria,

stromatolites– Global O2 pollution event

– <1 Ga • metazoans (multicellular

organisms)

– <600 Ga• reefs formed by varying

dominant species

– <~200Ma• Planktonic, calcareous

organism (Foraminifers, Coccoliths)

• Calcareous, pelagic ooze

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• Reef Forming Organisms

– Carbonate buildups with a rigid (intergrown) framework

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• Changes in Vegetation

– >400 Ma• no land plants

– >~100 Ma• no angiosperms (plants with only

minimal root systems)

– >~30 Ma• no grasses

• Strong influence on:– physical and chemical weathering– terrestrial sedimentation

• aeolian and fluvial depositional systems

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Atmosphere and Atmospheric Circulation

• Early Atmosphere– N2 & CO2 dominated (volcanic emanations)

• Advent of life and evolution of Photosynthesis– ~2000 Ma

• Production of O2

• Stage is set for heterotropy (non-photosynthesizing organisms)

– >~2000 Ma• BIF (Banded Iron Formation) chert +/- Fe+3

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Cause/Effect of Atmospheric Composition and Circulation

• Biological activity – CO2/O2

– Photosynthesis/respiration through time

• Weathering– Urey equation

gas + rock - > foram + diatom

CO2 + CaSiO3 -> CaCO3 + SiO2 • Continent and Topographic

Configuration• Polar Ice Cap advance/ retreat &

atmospheric circulation (AP driven circulation cells)

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Cause/Effect of Atmospheric Composition and Circulation

• Ocean Circulation– Effectiveness of CO2 solution in

the deep ocean

• Green House Effect: – Green House/Ice House

conditions

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Plate Tectonics/ Ocean Circulation/ Eustacy/Paleoclimates

• Intimately related and fundamental to the sedimentary record in Sedimentary Basins– Anorogenic Areas (little/slow) tectonism--> Climate and

Eustacy dominant on sedimentation• Chemical vs Physical weathering dominates• vegetation influences weathering (climate factors)• Eustacy dominates creation of accommodation space

– Orogenic Areas (rapid tectonism): Sedimentation strongly influenced by tectonism

• depositional systems with high relief• physical weathering dominates

• accommodation space mostly influenced by tectonics

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Plate Tectonics/ Ocean Circulation/

Eustacy/Paleoclimates • Late Cretaceous Changes in Plate Configuration, Topography

and Bathymetry (Hypsography), and Paleoclimates

1. High sea floor spreading rates/greater total length of MOR

6. Lesser production of terrigenous clastics

2. Elevated eustatic sea level 7. Less atmospheric CO2 sequestered in weathering (CO2 emissions from volcanism)

3. Globally subdued topography (fewer convergent plate boundaries)

8. Warmer Climate/ocean (5-10oC > than today); Diminished/slowed thermohaline circulation

4. Greater % of Earth surface is ocean 9. Less atmospheric CO2 sequestered in the deep ocean

5. Areally extensive epicratonic seas and greater production of carbonate sediments

10. Change in the position of the CCD; etc

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Climate Forcing Factors

• Amount and distribution of solar radiation

• Milankovitch Cycles– Orbital eccentricity (shape of

Earth orbital path)

– Rotational axis obliquity (axis tilt)

– Rotational axis precession (axis wobble)