Geologic Processes
Environmentally important on both long and short time scales
Outline
Geologic Time Scale
Composition of Earth
Plate tectonics
Rock cycles
Surficial geologic processes
Identification of environmental problems
Geologic Time Scale
Earth Origin 4.5 Ga
Origin of Life 3.8 Ga
Origin of Photosynthesis 3.5 Ga
O2 Atmosphere 2.0 Ga
Geologic Time Scale (con’t)
Multicellular Marine Orgs 680 Ma
Early Fishes 500 Ma
Life on Land 400 Ma
Coal Forming Forests 300 Ma
Mammals, Dinosaurs 240 Ma
Rise of Angiosperms 100 Ma
Origin of Hominids 1 Ma
Origin of Homo sapiens 70 ka
Connections
Atmospheric O2 depletion would take about 1 million years if Ps stopped. (Iron oxides)
Atmospheric CO2 depletion in the history of the Earth by sedimentation as carbonates, and organic sediments (fossil fuels).
Composition of the Earth
Remember composition of the atmosphere?
Nitrogen 78%, Oxygen 21%, Argon 1%, Other
Crust: O, Si, Al, Fe, Ca, Na, K, Mg
Mantle: Fe, O, Si, Mg
Core: Fe, Ni
Earth’s Crust
Oxygen 46.6 %
Silicon 27.7 %
Aluminum 8.1 %
Iron 5 %
Calcium 3.6 %
Sodium 2.8 %
Potassium 2.6 %
Magnesium 2.1%
All others 1.5 %
Plate Tectonics
The Restless Earth by Nigel Calder 1973
Prior theories: Continental drift, shrinking core, wrinkling crust
Earth’s lithosphere is made up of plates sliding on the asthenosphere
Plate boundaries
divergent
Oceanic ridges, rift valleys
convergent
Oceanic trenches
transform fault
San Andreas Fault
Why are we interested in Plate Tectonics?
Earthquakes
Volcanism
Movement and concentration of useful ore materials
Rock Cycle
Connections: Geosphere/Biosphere
Surficial Geologic Processes
Weathering
Erosion
Transportation
Mass wasting
Deposition
Weathering Definition
Weathering - chemical and mechanical alteration of rock materials during exposure to air, moisture, and organic matter.
Weathering Processes
Mechanical break down
rain impact
freeze / thaw
temperature fluctuations / expansion and contraction
hydration / shrinking and swelling
Chemical alteration
oxidation
dissolution, substitution
migration
pH change
Soil Formation and Weathering
Soils are formed by weathering of substrate.
Weathering is a natural process.
Natural soil renewal depends on natural weathering rates.
What is Soil?
Soil develops as a result of the interaction between:
Substrate
Climate
Organisms
Substrate Examples
Rock (Igneous, metamorphic, sedimentary)
Colluvium
Clay, silt or sand water-deposited sediments
Silt or sand wind-blown deposits
Volcanic ash
Erosion
Erosion - physical and chemical breakdown of rock, loosening and removal from point of origin
Transportation
Transportation - movement of products of weathering and erosion
Mass-Wasting
Mass Wasting - movement of regolith down-slope by means of gravity without aid of water, wind, ice, etc.
Deposition
Sedimentation (water deposits)
Colluvium (deposited by mass-wasting)
Wind deposits (Sand dunes and loess)
Glacial moraines
Why are we interested in surficial processes?
Weathering provides soil renewal, plant nutrients, and deteriorates buildings and bridges.
Erosion causes loss of productive soil.
Transportation results in water pollution.
Mass-wasting is a hazard.
Deposition results in siltation of streams, lakes and reservoirs, increases flood hazard.
Summary
Geologic Time Scale
Composition of Earth
Plate tectonics
Rock cycles
Surficial geologic processes
Identification of environmental problems