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Textbook of Geology > Structure of the Earth > Flashcards

Structure of the Earth Flashcards

1
Q

Shape of the Earth

A

Oblate Spheroid

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2
Q

Equatorial Radius of Earth

A

6378.388km or 6371 km

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3
Q

Polar Radius of Earth

A

6356.912 km

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4
Q

Inferences obtained thru siesmological studies

A

Primary, secondary, and Rayleigh waves

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5
Q

Depth of Mantle

A

2900 kms

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6
Q

Thickness of crust

A

33 kms

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7
Q

Factors that gives evidences regarding the existence of minor discontinuities within the earth

A
  1. Changes in the chemical composition of material
  2. Changes in the density
  3. Changes in the state of material i.e., whether its in liquid, solid or viscous state
  4. Changes in the physical properties
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8
Q

Thickness of crust in oceanic, continental, and orogenic belts respectively

A

Oceanic: 5 to 10 km
Continental: 35 kms
Orogenic Belt: 55 to 70 kms

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9
Q

Separates the sial layer from the underlying sima layer. Located at a depth of 11kms.

A

Conrad Discontinuity

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10
Q

Subdivision of crust

A

Sial and Sima

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11
Q

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.

A

Sial

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12
Q

Known as lower continental crust. Thickness of about 22kms. Rich in magnesium and silica

A

Sima

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13
Q

Extends up to depth of 19kms and comprises rocks of intermediate composition

A

Outer sima

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14
Q

Located at depths of 19kms and extends upto 33kms. Composition of basic to ultrabasic.

A

Inner sima

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15
Q

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.

A

Mantle

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16
Q

Upper mantle has a mix of 3 parts of ultramafic rocks and 1 part of basalt, whats the mixture called?

A

Pyrolite

17
Q

At 950 km depth it marks the lower limit of the very rapid rise in the velocity of seismic vibrations

A

Repetti Discontinuity

18
Q

Separates the mantle from the core

A

Guttenberg Discontinuity

19
Q

Extends from 2900 to 4982kms. Considered to be a state of homogenous fluid and it does not transmit S-waves.

A

Outer core

20
Q

It is a transition layer, extends from 4982 km to 5121 km. Material is fluid to semi-fluid state.

A

Middle Core

21
Q

Believed to contain metallic nickel and iron and is called ‘nife’. Solid with about a density of 18. Thickness is about 1250 km.

A

Inner Core

22
Q

Estimated central temp of earth

A

6000 C

23
Q

Central pressure of earth

A

392 x 10^8 bars in CGS unitsDe

24
Q

Density at the center of Earth

A

18 gm/cm^3

25
Q

Constitutes the upper part of the crust up to 16 km in depth

A

Lithosphere

26
Q

Layer below the lithosphere which virtually has no strength to resist deformation

A

Asthenosphere

Textbook of Geology (7 decks)

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