04. Komposisi Dan Struktur Bumi
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Transcript of 04. Komposisi Dan Struktur Bumi
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Pertemuan 4
KOMPOSISI DANSTRUKTUR BUMI
PENGANTAR ILMU KEBUMIAN
DAN SUMBER DAYA MINERAL
firdaus ([email protected])
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Earths Componentso Earths surface = ~30% land, ~70% water
o unlike any other known planeto Hydrosphere = includes oceans, lakes, seas, rivers, &
groundwatero Cryosphere = glaciers, snow, and sea ice
o Earths surface is not flat;it has topography
o Ignoring oceans, Earthssurface is dominated bytwo distinct elevations:o Most land is 0-2 km
above sea levelo Most of the sea floor
is 3-5 km below sealevel
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Earths Components
Bulk Earthcomposition
o Most abundant elementso Fe, O, Si, Mg
o Most common mineralsconsist of silica (SiO2) mixedin varying proportions with
other elements such as Fe,Mg, Al, Ca, K, Nao Felsic = more silica (less
Fe/Mg) & less denseo E.g. Granite
o Mafic = less silica (moreFe/Mg) & more denseo E.g. Gabbro / Basalt
35%
30%
15%
10%
10%
o Range: Felsic / Intermediate/ Mafic / Ultramafic
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Earth Materials
Unsur unsur yang menyusun material bumi.
Senyawa Organik Mengandung Senyawa Carbon.
Sebagian besar sisa-sisa mahluk hidup.
Termasuk Kayu, gambut, batubara dan minyak.
Terurai dengan kontak oksigen.
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Earth Materials Unsur unsur yang menyusun material bumi.
Mineral Solid Kristalin anorganik. Penyusun batuan.
Umumnya batuan : silikat (Si dan O).
Glas Mineral Non-Kristalin.
Struktur terbentuk saat mendingin terlalu cepat
Batuan Agregat mineral. There are many types.
Igneous Cooled from a liquid (melt).
Sedimentary Debris cemented from pre-existing rock.
Metamorphic Rock altered by pressure and temperature.
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Earth Materials Metal Padatan yang tersusun dari unsur logam.
Melt batuan yang dipanaskan berubah menjadi liquid. Magma Batuan cair bawah permukaan.
Lava Batuan cair di permukaan.
Volatil Material berubah jadi gas di temperatur
permukaan. H2O, CO2, CH4, dan SO2 Volatil berasal dari erupsi gunung api.
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Earths Density Densitas Bumi sebagai petunjuk tentang struktur internal
D ensit y = M a s s/ V o lum e Measures how much mass is in a given volume.
Expressed in units of mass/volume e.g. g/cm3
Ice floatswhy?
Estimates of earths mass and volumegive a whole earth density of ~5.5g/cm3
Typical rocks at the surface of theEarth have a density of 2.0-2.5 g/cm3
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Earths LayersBentuk Bumi sebagai petunjuk lapisan bumi
Jika bumi terdiri dari kulit padat tipis yang berada diatas suatulapisan liquid, maka permukaan bumi akan naik turun sepertilaut.
Maka, Kerak tidak mengapung diatas lapisan cair
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A Layered Earth
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.
Changes with depth. Pressure.
Temperature.
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The Earth (and other planets) have layered interiors.
Crust
Continental
Oceanic
Mantle
Upper
Lower Core
Outer Liquid
Inner Solid
Earths Interior Layers
W. W. Norton10Firdaus- PIK&SDM, 2012
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The Crust The outermost skin of Earth with variable thickness.
Thickest under mountain ranges (70 km 40 miles).
Thinnest under mid-ocean ridges (3 km 2 miles).
The Mohorovii discontinuity or Moho is the lowerboundary.
Separates the crust from the upper mantle.
Discovered in 1909 by Andrija Mohorovicic.
Marked by a change in the velocity of seismic P waves.
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Two Types of Crust
Continental crust Underlies the continents.
Avg. rock density about 2.7 g/cm3. Avg. thickness 35-40 km.
Felsic composition. Avg. rock type = Granite
Oceanic crust Underlies the ocean basins.
Density about 3.0 g/cm3
. Avg. thickness 7-10 km.
Mafic composition
Avg. rock type =
Basalt/Gabbro
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Two Types of Crust Crustal density controls surface position.
Continental crust Less dense; floats higher.
Oceanic crust
More dense: floats lower.
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Crustal Composition
98.5% of the crust is comprised of just 8 elements.
Oxygen is (by far!) the most abundant element in the crust. This reflects the importance of silicate (SiO2-based) minerals.
As a large atom, oxygen occupies ~93% of crustal volume.
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Bulk Earth Composition
35%
30%
15%
10%
10%
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Earths Mantle Solid rock layer between the crust and the core.
2,885 km thick, the mantle is 82% of Earths volume. Mantle composition = ultramafic rock called peridotite.
Below ~100-150 km, the rock is hot enough to flow.
It convects: hot mantle rises, cold mantle sinks.
Three subdivisions: upper, transitional, and lower.
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The Core
An iron-rich sphere with a radius of 3,471 km.
2 components with differing seismic wave behavior.
Flow in the outer core generates the magnetic field.
Outer core
Liquid iron-nickel-sulfur
2,255 km thick
Density 10-12 g/cm3
Inner core
Solid iron-nickel alloy
Radius of 1,220 km.
Density 13 g/cm3
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Lithosphere-Asthenosphere The Crust, Mantle, Core boundaries
defined by compositionbut sometimes we want to divide the layers of the Earth by their
behavior or physical properties
Lithosphere The brittle portion of Earths interior.
Behaves as a non-flowing, rigid material.
The material that moves as tectonic plates.
Made of 2 components: crust and upper mantle.
Asthenosphere The ductile portion of Earths interior. Shallower under oceanic lithosphere.
Deeper under continental lithosphere. Flows as a soft solid.
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Boundaries Between Layers The Crust-Mantle boundary = Moho
defined by seismic discontinuity indicating significant change incomposition.
Lithosphere-Asthenosphere boundary = Brittle-ductiletransition
Defined by a significant change in rock physical properties(viscosity)
Also defined as the depth below which earthquakes do not occur.
Lithosphere Crust
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Igneous Environments
Rocks are composed of an aggregate of one ormore minerals.
One exception: obsidian (rock) is composed of
volcanic glass with no orderly internalarrangement of atoms.
Three rock types.
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Igneous Rocks
Igneous rocks: rocks born of fire; alligneous rocks were once molten.
Intrusive igneous rocks cool and solidify
deep inside earth.
Form from solidified magma.
Extrusive igneous rocks cool andsolidify on earths surface.
Form from solidified lava.
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Igneous Rock Pictures
Intrusive (Plutonic) Igneous Rock Extrusive (Volcanic) IgneousRock
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Sedimentary Rocks
Sedimentary rocks are composed ofsediment.
Sediment can be either clastic (pieces) or chemical.
Clastic sediment is pieces of pre-existing rock likegravel, sand, silt and clay.
Chemical sediment is chemicals dissolved in water.
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Sedimentary Rock Pictures
Gravel clasts. Chemical sedimentaryrock.
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Metamorphic Rocks
Metamorphic rocks: Changed by heat and
pressure. Change is accomplishedwithout melting.
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Rock Cycle
One of the three rock types can become anyother rock type through various geologicprocesses. This is known as the rock cycle.
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Rock Cycle Diagram
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