Structure of the Earth Flashcards
Shape of the Earth
Oblate Spheroid
Equatorial Radius of Earth
6378.388km or 6371 km
Polar Radius of Earth
6356.912 km
Inferences obtained thru siesmological studies
Primary, secondary, and Rayleigh waves
Depth of Mantle
2900 kms
Thickness of crust
33 kms
Factors that gives evidences regarding the existence of minor discontinuities within the earth
- Changes in the chemical composition of material
- Changes in the density
- Changes in the state of material i.e., whether its in liquid, solid or viscous state
- Changes in the physical properties
Thickness of crust in oceanic, continental, and orogenic belts respectively
Oceanic: 5 to 10 km
Continental: 35 kms
Orogenic Belt: 55 to 70 kms
Separates the sial layer from the underlying sima layer. Located at a depth of 11kms.
Conrad Discontinuity
Subdivision of crust
Sial and Sima
Also known as the upper continental crust. Consists of all types of rocks exposed at land surface. Rich in aluminum and silica. Composition is granitic to granodioritic.
Sial
Known as lower continental crust. Thickness of about 22kms. Rich in magnesium and silica
Sima
Extends up to depth of 19kms and comprises rocks of intermediate composition
Outer sima
Located at depths of 19kms and extends upto 33kms. Composition of basic to ultrabasic.
Inner sima
Separated from the overlying crust by the Mohorovicic Discontinuity which is a first order discontinuity. Thickness of about 2865 kms. Forms 83% of earth BY VOLUME and 68% by MASS. Material is olivine-pyroxene complex which exists in solid state.
Mantle
Upper mantle has a mix of 3 parts of ultramafic rocks and 1 part of basalt, whats the mixture called?
Pyrolite
At 950 km depth it marks the lower limit of the very rapid rise in the velocity of seismic vibrations
Repetti Discontinuity
Separates the mantle from the core
Guttenberg Discontinuity
Extends from 2900 to 4982kms. Considered to be a state of homogenous fluid and it does not transmit S-waves.
Outer core
It is a transition layer, extends from 4982 km to 5121 km. Material is fluid to semi-fluid state.
Middle Core
Believed to contain metallic nickel and iron and is called ‘nife’. Solid with about a density of 18. Thickness is about 1250 km.
Inner Core
Estimated central temp of earth
6000 C
Central pressure of earth
392 x 10^8 bars in CGS unitsDe
Density at the center of Earth
18 gm/cm^3
Constitutes the upper part of the crust up to 16 km in depth
Lithosphere
Layer below the lithosphere which virtually has no strength to resist deformation
Asthenosphere
