interior of earth

Department of Mining Engineering,UET,Lahore

Interior of earth ?

Evidence of interior of earth ?

Chemical composition of earth ?

Department of Mining Engineering, UET,Lahore


Interior of Earth Crust

Mass 1.7 % of earths mass

Depth from surface :5150-6370 km (1220km)

Suspended in molten outer core

Solidification due to decrease in temperature and increase in pressure


Mass 30.8% of earths mass

Depth 2890-5150 km (2260km)

Molten material

Less dense

Earth magnetic field

Not pure iron ,some other light elements


Mass 3% of earth mass

Depth 2700km-2890 km (200-300km)

4 % of mantle –crust mass

Part of mantle sink through it but floating on outer core due to its low density as compared to outer core


49.2% mass of total earths mass

Depth 650-2890km

72.9% mantle –crust mass


Mass 7.5% of earth mass Depth 400-650 km 11.1 % of mantle –crust mass Fertile layer : production of basaltic magma Conversion into dense material


10.3 % of earth mass

Depth 10-400km

15% of mantle –crust mass

Asthenosphere


.099% of earth mass

0-10 km depth

0.147% of mantle –crust mass

A large area for volcanoes


0.374% of earth mass

Depth 0-50km

0.544 % of mantle-crust mass


Drilling up to 15 KM

Direct reach is impossible ?

Indirect and accurate evidences for interior.


Density

Meteorites

Moment of inertia

Magnetic field

Volcano

Seismic waves


Earth density = 5.5 gram per cubic centimeter

Density of crust( continental ) = 2.7 gram per cubic centimeter

Density of crust (oceanic part) = 3 gram per cubic centimeter

It mean inner rocks are more dense .


Meteorites: material that falls to Earth falls into three basic categories

Chondrites: Undifferentiated material thought to represent the material of the Solar Nebula. Contain homogeneously mixed rocky and metalicsubstances. Most meteroites fall into this catagory.

Stony meteorites: Differentiated meteorites containing lighter silicate material.

Iron meteorites: Meteorites consisting of metals, primarily iron and nickel, usually in interlocking crystals


A measure of distribution of mass within an object that determines the ease with which it rotates.

Ice skater

Mass concentrated in centre ,less moment of inertia and ease in rotation

Earth’s moment of inertia 15 times less than an identical sphere of uniform density.


Centre consist major element = iron Symmetrical magnetic filed .

Early ideas about what caused the compass needle to point toward the northincluded some divine attraction to the polestar (North Star), or attraction to largemasses of iron ore in the arctic.

A more serious hypothesis considered the Earth or some solid layer within theEarth to be made of iron or other magnetic material forming a permanent magnet.There are two major problems with this hypothesis. First, it became apparent thatthe magnetic field drifts over time; the magnetic poles move. Second, magneticminerals only retain a permanent magnetism below their Curie temperature (e.g.,580°C for magnetite). Most of the Earth's interior is hotter than all known Curietemperatures and cooler crustal rocks just don't contain enough magnetic contentto account for the magnetic field and crustal magnetization is very heterogeneousin any case.

The discovery of the liquid outer core allowed another hypothesis: thegeodynamo. Iron, whether liquid or solid, is a conductor of electricity. Electriccurrents would therefore flow in molten iron. Moving a flowing electric currentgenerates a magnetic field at a right angle to the electric current direction (basicphysics of electromagnetism). The molten outer core convects as a means ofreleasing heat. This convective motion would displace the flowing electric currentsthereby generating magnetic fields. The magnetic field is oriented around the axisof rotation of the Earth because the effects of the Earth's rotation on the movingfluid (coriolis force).


A volcano is a rupture on the crust ofa planetary mass object, such as the Earth,which allows hot lava ,volcanic ash,and gases to escape from a magma chamberbelow the surface.


Igneous rocks that have cooled from magma contain lumps of rock of different composition from the magma itself. These lumps are termed xenoliths, which means ‘foreign piece of rock’. The xenoliths are formed when magma rising from deep levels rips off pieces of the rock which it passes through (the country rock) and carries these pieces along with it. Some xenoliths come from deeper levels within the crust, others come from the uppermost mantle, down to depths of about 200 km. The mantle xenoliths show us that the uppermost mantle is made of a rock called peridotite.


Oceanic crust is normally destroyed less than 200 Myr (million years) after formation by subduction. An ophiolite is the technical term for a piece of ancient oceanic crust that escaped destruction and was instead shifted onto a continental plate by natural tectonic forces. Rock exposures cut through ophiolites allow us to piece together the structure of oceanic crust and the uppermost mantle beneath. The mantle part of ophiolites consists of peridotite, similar to that brought up in xenoliths.

The difficulty with using ophiolites to infer mantle composition is that they have sometimes been heavily deformed and chemically altered by the tectonic forces that shifted them onto the continent.


Non-volcanic passive margins (also known as rifted margins) are plate boundaries where continental crust is rigidly attached to oceanic crust. Non-volcanic passive margins form a class of passive margins that has been discovered within the past few decades. At non-volcanic margins, a transition zone exists between the continental and oceanic crust in which mantle is exposed at the seabed. The mantle is made of peridotite that has undergone major chemical alteration by interaction with seawater.


Surface waves = moves along surface

Body waves divided into P waves & S waves

P (primary) waves pass through liquid & solids

S (secondary) waves pass through solid only.


Vp=

[(c+4/3R)÷p]1/2

Vs =(R/p) ½

C =

Incompressibility

p = density

R= Rigidity of

substance


Seismic waves travel more quickly through denser materials and therefore generally travel more quickly with depth.

Hot areas slow down seismic waves.

Seismic waves move more slowly through a liquid than a solid.

Partially molten areas may slow down the P waves and attenuate or weaken S waves.


Mohorovicic Seismic Discontinuitybeyond 200 km the seismic waves arrive sooner than expected, forming a break in the travel time vs. distance curve.

Mohorovicic (1909) interpreted this to mean that the seismic waves recorded beyond 200 km from the earthquake source had passed through a lower layer with significantly higher seismic velocity.

This seismic discontinuity is now know as the Moho (much easier than "Mohorovicic seismic discontinuity") It is the boundary between the felsic/mafic crust with seismic velocity around 6 km/sec and the denser ultramaficmantle with seismic velocity around 8 km/sec. The depth to the Moho beneath the continents averages around 35 km but ranges from around 20 km to 70 km. The Mohobeneath the oceans is usually about 7 km below the seafloor.


Low Velocity ZoneSeismic velocities tend to gradually increase with depth in the mantle due to the increasing pressure, and therefore density, with depth. However, seismic waves recorded at distances corresponding to depths of around 100 km to 250 km arrive later than expected indicating a zone of low seismic wave velocity. Furthermore, while both the P and S waves travel more slowly, the S waves are attenuated or weakened. This is interpreted to be a zone that is partially molten, probably one percent or less (i.e., greater than 99 percent solid). Alternatively, it may simply represent a zone where the mantle is very close to its melting point for that depth and pressure that it is very "soft." Then this represents a zone of weakness in the upper mantle. This zone is called the asthenosphere or "weak sphere."


The asthenosphere separates the strong, solid rock of theuppermost mantle and crust above from the remainder of thestrong, solid mantle below. The combination of uppermostmantle and crust above the asthenosphere is calledthe lithosphere. The lithosphere is free to move (glide) over theweak asthenosphere. The tectonic plates are, in fact, lithosphericplates.

670 km Seismic DiscontinuityBelow the low velocity zone are a couple of seismic discontinuities at which seismic velocities increase. Theoretical analyses and laboratory experiments show that at these depths (pressures) ultramafic silicates will change phase (atomic packing structure or crystalline structure) from the crystalline structure of olivine to tighter packing structures. A discontinuity at around 670 km depth is particularly distinct.

The 670 km discontinuity results from the change of spinel structure to the perovskite crystalline structure which remains stable to the base of the mantle. Perovskite (same chemical formula as olivine) is then the most abundant silicate mineral in the Earth. The 670 km discontinuity is thought to represents a major boundary separating a less dense upper mantle from a more dense lower mantle.


Gutenberg Seismic Discontinuity / Core-Mantle Boundary (shadow zone 103 to 143)Seismic waves recorded at increasing distances from an earthquake indicate that seismic velocities gradually increase with depth in the mantle .However, at arc distances of between about 103° and 143° no P waves are recorded. Furthermore, no S waves are record beyond about 103°. Gutenberg (1914) explained this as the result of a molten core beginning at a depth of around 2900 km. Shear waves could not penetrate this molten layer and P waves would be severely slowed and refracted (bent).


Lehman Siesmic Discontinuity / The Inner CoreBetween 143° and 180° from an earthquake another refraction is recognized (Lehman, 1936) resulting from a sudden increase in P wave velocities at a depth of 5150 km. This velocity increase is consistent with a change from a molten outer core to a solid inner core.


Core is made of iron with minor amounts of nickel, and lies at the center of the earthMantle is made of iron-magnesium silicates and surrounds the core. The mantle makes up the bulk of the earth.Crust occurs as two distinct types, oceanic crust and continental crust. Both types of crust are lighter (less dense) and contain more silica than the mantle.

Oceanic crust is the crust that underlies most of the areas we call "oceans" it is thinner, is more dense, and contains less silica and aluminum and more magnesium and iron than continental crust. The lack of silica makes it darker than continental crust.

Because continental crust is thicker and made of less dense material than the oceanic crust, it "floats" higher on the earth.


Granitic continental crust

Basaltic oceanic crust

Magma is mefic (megnasium & iron ) with light elements such as silicon ,oxygen and aluminum

Ultrmefaic (mantle) higher densities than mefic

Diatremes = diamond bearing ultramaficrocks

Felsic = iron silicates


interior of earth

Education

earth mass depth

lahore mass

lahorelower mantle mass

earths interior earth

earth mass0

earth massdepth

lahoreinner core mass

lahoreouter core mass