Asteroids
● Apart from the stars, planets and satellites, there are numerous
tiny bodies which also grate around the sun in an elliptical
path. These bodies are called asteroids.
● They are found between the orbits of Mars and Jupiter.
● The largest asteroid is the Ceres.
● NASA has launched the Don Mission for the study of asteroids.
● Near Schumacher is the first plane which landed on an
asteroid.
Meteoroids
● A meteorite is a solid piece of debris from an object, such as a
comet, asteroid, or meteoroid that originates in outer space
and survives its passage through the atmosphere to reach the
surface of a planet or moon.
● When meteoroids enter Earth's atmosphere (or that of another
planet, like Mars) at high speed and burn up, the fireballs or
“shooting stars” are called meteors.
● When a meteoroid survives a trip through the atmosphere and
hits the ground, it's called a meteorite.
Comets
● Comets are made up of frozen gases which hold together rocky
and metallic materials.
● A comet is characterized by a long luminous tail, which emits
light but this is visible only when the comet's orbit passes close
to the Sun.
● Comets move around the Sun in regular orbits, but their orbits
are elongated ellipses that it takes them hundreds and,
sometimes even thousands of years to complete one revolution
around the Sun.
● A comet becomes visible only when it travels close to the Sun.
Its ice melts to a head of gas called a Coma and dust particles
are also swept back to form a dust tail.
Solar Eclipse
● Also known as the eclipse of the sun, it occurs when the moon
comes in between the sun and the earth.
● As a result, the moon blocks the light of the sun from reaching
the earth’s surface and casts a shadow on it.
● This occurs on a new moon phase. We can observe up to 5 solar
eclipses per year.
Lunar Eclipse
● Also known as the eclipse of the moon, it occurs when the
earth comes in between the sun and the moon.
● As a result, the earth blocks the light of the sun from
reaching the moon’s surface and casts its shadow on the
moon. It occurs on a full moon day.
● We can observe up to 3 lunar eclipses per year.
Structure of the Earth
● The Internal structure of Earth is divided into three concentric
parts:
1. Crust
2. Mantle.
3. Core
Major Discontinuity Division of the earth's interior
Konrad discontinuity Separates the upper crust and the lower
crust.
Moho discontinuity Separates crust and mantle.
Repeti discontinuity Separates the upper mantle and the lower
mantle.
Gutenberg Separates the mantle and core
discontinuity
lehmann Separates the upper core and the lower core.
discontinuity
Note : moving downwards from surface to inner part of earth,
temperature increases at the rate of 25 – 30 degree C per kilometer.
The lithosphere
● The lithosphere (10-200 km) is the Outermost and mechanical
layer of the Earth that consists of the entire crust and the
top-most portion of the mantle.
● Mechanically, the Earth's layers can be divided into lithosphere,
Asthenosphere (80-200 km), Mantle, Outer core, and inner core.
● Chemically, Earth can be divided into-
➔ The crust (8−40 kms)
➔ Upper mantle (640 km)
➔ lower mantle (660 - 2700)
➔ Outer core (2200 km)
➔ Inner core (1200 km)
Crust
○ It is the Outermost solid part of the earth, normally
about 8-40 kms thick.
○ The crust is the outermost layer of the earth.
○ It is made up of 0.5−1.0 percent of the earth's volume.
○ The density of the crust is 3 g/cm3.
○ It is thicker in the region of the continents and thinner
in the region of the ocean floors.
○ The thickness of the lithosphere is 10 to 200 km.
○ The average thickness of the Continental crust of earth
is 30 km.
○ Major constituent elements of crust are Silica (Si) and
Aluminium (Al) and thus, it is often termed as SIAL
(Sometimes SIAL is used to refer to Lithosphere, which is
the region comprising the crust and uppermost solid
mantle, also).
○ It is about 35 km on the continental masses and only 5 km
on the ocean floors.
○ The Mean density of the materials in the crust is 3g/cm3.
Mantle
○ The portion of the interior beyond the crust is called as
the Mantle.
○ The layer of earth that separates the crust from the core
is Mantle.
○ The Upper portion of the mantle is called the
Asthenosphere.
○ The Asthenosphere is a layer in the Earth's upper mantle
that is partially molten and exhibits a plastic or semi-fluid
behavior.
○ It is located beneath the lithosphere and plays a crucial
role in the movement of tectonic plates.
○ The Asthenosphere is characterized by lower seismic wave
velocities and higher attenuation compared to the
overlying lithosphere.
○ Mantle makes up 52⁒ of total earth’s mass.
○ Its thickness is about 2900 km and the density of
substances in the mantle ranges from 3.0 to 4.7.
Core
○ It is the innermost layer surrounding the earth’s center
with a radius of about 3500 km.
○ The crust forms only 0.5 per cent of the volume of the
earth , 16 percent consists of the mantle and 83 per cent
makes the core . The radius of the earth is 6371 km .
○ The Core consists of two sub-layers: the inner core and the
outer core.
○ The inner core is in solid state and the outer core is in the
liquid state (or semi-liquid).
○ It is composed mainly of Iron (Fe) and Nickel (Ni) and
hence it is also called as NIFE.
○ The core is the densest layer of the earth with its density
ranges between 9.5-14.5g/cm3.
○ After the mantle, the earth's density goes on increasing
rapidly towards its center and finally is more than 13.
The temperature of the central part of the earth may be about
5000°C.
Rocks
○ The solid parts of the earth's crust are called rocks. In
other words, Any natural mass of mineral matter that
makes up the earth's crust is called Rocks.
○ Rocks are made up of two or more minerals.
○ Rocks are classified in three main types depending on the
process of their formation:
● Igneous
● Sedimentary
● Metamorphic
Petrology:- Branch of geology that studies the origin , composition,
distribution, and structure of rocks.
Igneous Rocks
○ Igneous rock is formed through the cooling and
solidification of hot magma or lava.
○ They are called the primary rocks as all the other rocks
are formed directly or indirectly from the igneous rocks.
○ They are hard, granular and crystalline rocks, less
affected by chemical weathering.
○ There are No layers in igneous rocks, due to which the
penetration of water in them is very less.
○ Fossils are also not found in igneous rocks.
○ Examples of Igneous rocks are- Granite, Basalt,
Gabbro, Pegmatite and Peridotite.
The two main categories of igneous rocks are:-
● Extrusive rocks: Extrusive rocks are formed on the
surface of the Earth from lava, which is magma that
has emerged from underground.
● When this molten lava comes on the earth’s surface. It
rapidly cools down and becomes solid.
● Rocks formed in such a way on the crust are called
extrusive rocks. Examples: basalt.
● Intrusive rocks: Intrusive rocks are formed from
magma that cools and solidifies within the crust of the
planet.Since they cool down slowly, they form large
grains. Example granite.
Volcanic when lava cools and solidifies on earth.
rocks
Plutonic rocks from when magma cools and solidifies below earth
Hypabyssal an intrusive igneous rock that is emplaced at medium to
rocks shallow depths within the crust.
Granite -
● Granite is composed mainly of quartz and feldspar
with minor amounts of mica.
● Granite is the most abundant rock in the continental
crust.
● It is the Most common Igneous Rocks.
● These are igneous rocks that form when hot, molten
rock crystallizes and solidifies; means Granite Rocks is
formed by the cooling and crystallization of magma
Sedimentary Rocks
○ Sedimentary rocks are types of rock that are formed by
the accumulation or deposition of mineral or organic
particles at the Earth's surface, followed by cementation.
○ Sedimentation is the collective name for processes that
cause these particles to settle in place.
○ Lithification includes all the processes which convert
unconsolidated sediments into sedimentary rocks.
○ The Sedimentary rocks can be classified on the basis of
the nature of sediments:
○ Mechanically, Chemically and Organically formed rocks.
○ Depending upon the mode of formation, sedimentary
rocks are classified into three major groups.
Mechanically Sandstone, Conglomerate, limestone, Shale,
loess etc.
Organically Geyserite, Chalk, limestone, Coal etc.
Chemically Chert, limestone, Halite, Potash etc.
Metamorphic Rocks
○ Metamorphic rocks were once igneous or sedimentary
rocks, but have been changed (metamorphosed) as a
result of intense heat and/or pressure within the Earth’s
crust.
○ They are crystalline and often have a “squashed”
(foliated or banded) texture.
○ The agents of metamorphism are: heat, compression
and solution.
Original Rocks Metamorphic Rocks
Basalt Schist, Amphibolite
Sandstone Quartzite
Limestone Marbal
Shale and mudstone Slate
Granite Gneiss
Clay Slate
