Bsc first year

1. Internal structure of the Earth
The Earth is thought to have formed some 4.6 billion years ago.
The deepest borehole yet made is 10 km and mines are still shallower

2. •Direct observation about the internal structure of earth is not
possible, due to high temperature, pressure & depth.
•Deepest borehole made in earth is about 10 km, which is not
sufficient to get idea about the internal structure of the earth.
•Therefore, most of the evidences are indirect or logically derived or
inferred.
•Seismological data recently considered as reliable sources that help
to understand about the internal structure of earth and said that it
is divided into several layers distinguished by their physical and
chemical properties.

3. Evidence from Seismic Waves
Seismic waves
•Waves/energy generates due to sudden movement on earth’s
crust.
•Waves travels through earth resulting the internal structural of
the earth.
•The waves generated is recorded on seismograph.
Types of seismic waves
Seismic waves
Body waves
P-waves S-waves
Surface waves
Love Waves Rayleigh Waves

6. Earth’s interior
Based on the chemical composition, the interior of the earth is
composed of three different layers or the zone namely,
i. Crust
ii. ii. Mantle and
iii. iii. Core

7. Crust
•Outermost/topmost layer of the earth’s interior.
•Solid in nature and composed of heterogeneous material.
•Earth crust is divided into two types:- continental crust(30-50km) and
oceanic crust(5-10km).
•Temperature is upto 1600 degrees Celsius.
•The continental crust is composed of light color and low/light dense rock
called granitic rock whereas the oceanic crust composed of dark color and
heavier rock called basaltic type.
•Crust is divided into two different layers namely i. Sial and ii. Sima
separated by Conrad Discontinuity.

8. Mantle
•Second layer or the middle layer/zone
•Semi-liquid in nature and composed of homogenous material (high
density and high plasticity).
•Thickness of the mantle is 2900 kms.
•Temperature is about: (1600-7900) degree celcius.
•Covers 83% of the earth by volume and 68% by mass.
•Mantle composed of ultrabasic rock rich in aluminum and
magnesium.
•Ocean floor spreading, continental drift, orogeny and earthquake
have originates from this zone.
•Crust and Mantle is separated by Mohorovicic’s discontinuity or
simply Moho.

9. Core
•Innermost layer of the earth’s interior.
•Pressure and temperature at the core is extremely high. (7900-
11000°C temperature), 3 million atmospheric pressure).
•Constitutes about 17 % of the volume and 34% of the mass.
•Core generally composed of iron and nickel.
•Core is further divided into two different layers:
i. Inner core and ii. Outer core
Outer core: Liquid layer , less desne , Fe-Ni
Inner core: Solid layer, highly dense , Fe-Ni

10. • The inner core is solid because it is made of
very dense, or heavy, materials - like iron and
nickel. Even though it is very hot, these
materials don't "melt" very easily, so they stay
solid

11. There are five discontinuies inside the
earth

12. Based on Physical Properties
Lithosphere: comprises of crust and a part of upper
mantle. Brittle in nature, easily can be
broken/fracture. 100-200km thick
Asthenosphere: ductile in nature. 250km thick
Mesosphere: The lower mantle, 2500km thick,
Capable of flowing.

13. Important questions
• Describe internal structure of earth with neat
and labelled sketch.
• Short notes on:- Crust , mantle and Core.
• Short notes on lithosphere and
asthenosphere.
• What are the different internal boundaries?

14. Foliation and Lineation(5 marks)
Foliation:-
 The planar fabrics or compositional layering in metamorphic
rock is called foliation.
 One can see lines in all sides.
 It is disc or sheet shaped.
 Sandwich or sheet like structure.
 Primary and secondary are two types of foliation.
 Eg:- Muscovite

15. Lineation :-
 Linear fabrics or long axial orientation of minerals is called
lineation.
 One can see dotted structure in one side.
 It is cigar shaped.
 Needle like structure.
 Primary, secondary and inherited are 3 types of lineation.
 Eg:- tourmaline, kyanite etc