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

2Firdaus- PIK&SDM, 2012


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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

27Firdaus PIK&SDM 2012

04. Komposisi Dan Struktur Bumi

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