EARTHSC 1121 Lecture 7: 1/31

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Why we have deserts in some places and not in others, how does Earth create things that we use, understanding the
geological consequences that result in elemental deposits: Earth’s climate and what keeps it stable/regulates it (and how
does humans’ changing it affect or experience).
Surface features
Earth’s surface is dominated by water and land.
Water is a part of the hydrosphere.
Surface water
Ground water
Glacial ice
Impact craters occur rarely on Earth.
Removed by weathering and erosion
Unlike other planets in the Solar System
Earth’s surface reveals high continents and low ocean basins.
Position (the relative heights of these continents and basins) due to the differing
buoyancy of each type of crust
The crust effectively floats on the mantle
This was Lab #1.
Is Silly Putty a liquid or a solid?
“It takes the shape of its container” vs. “it IMMEDIATELY takes the shape
of its container”
Could argue that it is solid/liquid based on the time span, because it is
able to retain a bit of rigidity on short timescales.
The Earth’s mantle is solid. It is a fluid, but it is not a liquid
(meaning it will flow over long time spans, but not short
ones).
“Continental Drift” is why; “Plate Tectonics” are how.
Most land lies within 1 km of sea level.
Most ocean floors are close to 5 km depth.
Extremes of depth or height are rare.
There aren’t many “Mount Everest”s on the Earth.
The 2 dominant “levels” reflect continental vs. oceanic
crust.
[Hypsometric Curve pictured right]
Elemental Composition
~Ninety percent of Earth’s mass is comprised of 4 elements (this is by mass. If done by
moles, AKA counting atoms, oxygen would be most prominent).
Iron (Fe) ~35% (mostly in the core)
Oxygen (O) ~30% (takes up most of the volume of the mantle and crust)
Silicon (Si) ~15%
Magnesium (Mg) ~10%
The remaining 88 naturally-occurring elements?
Form ~10% of Earth.
A Layered Earth
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We live on the thin outer skin of Earth.
Will be called interchangeably the “Crust” (discussing composition of the rock
you’re standing on) and the “Lithosphere” (talking about the rigid part of the outer
part of the planet, as opposed to the Silly Putty-Mantle).
Early perceptions about Earth’s interior were wrong.
Open caverns filled with magma, water, and air.
Furnaces and flames.
We now know that Earth is comprised of layers.
The Crust
The Mantle
The Core
Outer Core
Inner Core
Several clues indicated a layered structure.
Density--
Average density greater than surface density.
Density must increase with depth.
Shape--
Mass further from center would result in a more flattened disk.
Solid interior--surface would have greater tides if it were pulled.
The Earth is 21 km wider at the equator than it is at the poles
Earthquake clues--Earthquake energy transmitted as seismic waves that pass through
Earth.
Seismic waves have been used to probe the interior.
Wave velocity changes with density.
Velocity changes give depth of layer changes
Echoes off of boundaries between layers bounce back to the surface
Changes with depth.
Pressure.
Temperature.
Rock type.
Earth’s Interior Layers
Earth (and other planets) have layered interiors.
Crust
Continental
Oceanic
Mantle
Upper
Lower
Core
Outer--liquid
Inner--solid
The Crust
The outermost “skin” of Earth with variable thickness.
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