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]]>Internal Structure of the Earth
The interior structure of the Earth, similar to the outer, is layered. These layers can be defined by either their chemical or their rheological properties. The earth has an outer silicate solid crust a highly viscous mantle a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of earth’s internal structure is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depts. by volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of the gravity field of the Earth, and experiments with crystalline solids at pressures and temperatures characteristic of the Earth’s deep interior.
Crust:
- Upper most zone/shell of the earth having the thickness of around 40 km in the continent and around 10 km in the ocean.
- It is relatively thin layer of solid rock on a liquid interior.
- The oceanic crust is made up heavier and dark rocks basalt, whereas the continental crust consists of light colored and light density granitic rocks.
Mantle :
- At the base of the crust (somewhere 35-40 km), the different materials from that of crust, nearly from a homogeneous zone till a depth of 2900 km.
- Consisting mostly of basic materials called ultra basic rocks rich in iron and magnesium but poor in silica.
Core:
- It is the innermost structural zone which starts at the depth of 2900 km below the surface and extends right up to the center of the earth at 6370 km .
- The materials do not have shear resistance which gives and idea of nearly liquid material.
- Have very high density above 10 gm/cc at the mantle core boundary.
- Have very high density above 10 gm/cc at the mantle core boundary.
Different between structure of earth and composition of earth:
| Structure of earth | Composition of earth |
| The study of the behavior of seismic waves tells us about the shape and composition of the interior of the Earth: Crust: 10–70 km, thick, intermediate composition Mantle: 2800 km, thick, mafic composition Outer core: 2200 km, thick liquid iron Inner core: 1500 km, thick solid iron | Seismology also tells us about the density of rocks: Continental crust: 2.8 g/cm3 Oceanic crust: 3.2 g/cm3 Asthenosphere: 3.3 g/cm3 |
The layer of the earth was determined by the abnormal behavior of seismic wave :
Shadow zone:
The zone of the earth where is no passage of seismic wave.
Plate tectonics:
Driving Mechanism of Plate Tectonics
- Thought to be convection of the mantle.
- Friction at base of the lithosphere transfers energy from the asthenosphere to the lithosphere.
- Convection may have overturned asthenosphere 4–6 times.
According to plate tectonics, the earth can be subdivided inti six large rigid plates and several smaller ones, the boundary of the plates is fixed by the foci of the earthquake epicenter. These plate are not stationery, the movements of these plates have been generalized into three main categories with respect to their mutual boundaries
- Divergent (Constructive )
- Convergent (Destructive)
- Transform fault (conservative)
Three Types of Plate Boundaries
- Transform:
At transform fault ( conservative) boundaires, plate slide horizontally past each other.
- Divergent:
At divergent ( constructive ) boundaries, plates move apart and create new lithosphere.
- Convergent:
At convergent ( destructive) boundaries, plate collide and one is pulled into the mantle and recycled.
Himalayas: Continents collide
Millions of years ago India and an ancient ocean called the Tethys Ocean were sat on a tectonic plate. This plate was moving northwards towards Asia at a rate of 10 centimeters per year. The Tethys oceanic crust was being subducted under the Asian Continent. The ocean got progressively smaller until about 55 milion years ago when India ‘hit’ Asia. Because both these continental landmasses have about the same rock density, one plate could not be subducted under the other. The pressure of the impinging plates could only be relieved by thrusting skyward, contorting the collision zone, and forming the jagged Himalayan peaks.
Source: https://journals.openedition.org/rga/2910
Source: https://pubs.usgs.gov/gip/dynamic/himalaya.html
Reference 1: Text book of Engineering Geology , N Chenna Kesavulu
Reference 2: https://en.wikipedia.org/wiki/Geology_of_Nepal#:~:text=The%20geology%20of%20Nepal%20is,going%20continent%2Dcontinent%20collision%20tectonics.
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