it is the only world in our solar system with liquid water on the surface
Equator – 3,963 miles (6,378 km)
Pole – 3950 miles (6356 km)
Difference – 13 miles (22 km)
Earth is the biggest of the terrestrial planets
150 million km distance from Sun
It takes about eight minutes for light from the Sun to reach our planet
It completes one rotation every 23.9 hours.
It takes 365.25 days to complete one trip around the Sun.
That extra quarter of a day presents a challenge to our calendar system, which counts one year as 365 days.
To keep our yearly calendars consistent with our orbit around the Sun, every four years we add one day. That day is called a leap day
Earth’s axis of rotation is tilted 23.4 degrees respect to its orbit
Interior of Earth
Due to gradual increase in density the temperature inside has increased. As a result the material inside started getting separated depending on their densities.
This allowed heavier materials (like iron) to sink towards the center of the earth and the lighter ones to move towards the surface.
With passage of time it cooled further and solidified and condensed into a smaller size. Interior of the Earth
This led to the development of the outer surface in the form of a crust.
During the formation of the moon, due to the giant impact, the earth was further heated up.
It is through the process of differentiation that the earth forming material got separated into different layers.
It composed of 4 main layers
The Earth Crust
It is the outermost solid part of the earth
Mean thickness of oceanic crust is 5 km
thickness of continental crust is around 30 km and its less dense
The continental crust is thicker in the areas of major mountain systems. It is as much as 70 km thick in the Himalayan region.
It is made up of heavier rocks having density of 3 g/cm3.
This type of rock found in the oceanic crust is basalt.
Major constituent elements of crust are Silica (Si) and Aluminium (Al) and thus, it is often termed as SIAL
SIAL is used to refer Lithosphere, which is the region comprising the crust and uppermost mantle
The discontinuity between the hydrosphere and crust is termed as the Conrad Discontinuity.
The mantle extends from Moho’sdiscontinuity to a depth of 2,900 km.
The upper portion of the mantle is called asthenosphere.
The word astheno means weak. It is considered to be extending upto 400 km.
It is the mainsource of magma that finds its way to the surface during volcanic eruptions.
It has a density higher than the crust’s
The lowermantle extends beyond the asthenosphere. It is in solidstate.
The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed as SIMA
The discontinuity between the upper mantle and the lower mantle is known as Repetti Discontinuity.
The portion of the mantle which is just below asthenosphere, but above the core is called as Mesosphere
The core-mantle boundary is located at the depth of 2,900 km.
The outer core is in liquid state while the inner core is in solid state
The density of material at the mantle core boundary is around 5 g/cm3
Temperature is between 4000 to 5000 C
At the centreof the earth at 6,300 km, the density value is around 13g/cm3
Temperature is between 5000 to 7000 C
The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the nifelayer.
Sources and Information about Interior
Most of our knowledge about the interior of the earth is largelybased on estimates and inferences
Direct sources are deep sea drilling project and volcanic eruption
Deep earth mining and drilling reveals the nature of rocks deep down the surface.
Mponeng gold mine and TauTona gold mine in South Africa are deepest mines reaching to a depth of 3.9 km
The deepestdrill at Kola, in ArcticOcean, has so far reached a depth of 12 km.
Meteors that reach the earth. Structure observed in the meteors are similar to that of the earth
Other indirect sources include gravitation, magnetic field, and seismic activity
Gravitation force (g)
It is not the same at different latitudes on the surface.
It is greater near the poles and less at the equator because of the distance from the core.
The reading of the gravity at different places is influenced by many other factors.
Such a difference is called gravityanomaly.
Gravity anomalies give us information about the distribution of mass of the material in the crust of the earth.
The study of seismicwavesprovides a complete picture of the layeredinterior
An earthquake in simple words is shaking of the earth.
It is caused due to release of energy, which generates waves that travel in all directions.
The release of energy occurs along a fault.
A fault is a sharp break in the crustal rocks.
Rocks along a fault tend to move in opposite directions.
The point where the energy is released is called the focus of an earthquake, also called the hypocenter
Point on the surface, nearest to the focus, is called epicenter
All naturalearthquakestakeplace in the lithosphere.
Seismograph records the waves reaching the surface
Earthquake waves are basically of two types – body waves and surface waves.
It generates due to the release of energy at the focus and move in all directions traveling through the body of the earth.
Velocityofwaveschanges as they travelthroughmaterialswith different densities.
The denser the material, the higher is the velocity.
Their direction also changes as theyreflect or refract when comingacrossmaterialswithdifferentdensities
The variations in the direction of waves are inferred with the help of their record on seismograph
There are two types of body waves P and S-waves
They move faster and the first to arrive at the surface.
These are also called ‘primarywaves’
P-waves are similartosoundwaves.
They travel through gaseous, liquid and solid materials.
They vibrateparallel to the direction of the wave.
It creates density differences in the material leading to stretching and squeezing of the material
They arrive at the surface with some time lag.
These are called secondarywaves.
they can travelonlythroughsolid materials
It has helped scientists to understand the structure of the interior of the earth.
Direction of vibrations of S-waves is perpendiculartothewavedirection in the vertical plane.
They create troughs and crests in the material through which they pass.
Body waves interact with the surface rocks and generate new set of waves called surface waves.
These waves move alongthesurface
They are the last to report on seismograph.
These waves are moredestructive, cause displacement of rocks, and hence, the collapse of structures occurs.
They are mainly two types Rayleigh Waves (R waves) and Long Waves (L Waves).
Long waves are the ones that cause maximum destruction to the buildings.
Their order of appearance is – PSLR on seismograph
Some specific areas where the waves are not reported, is called ‘shadow zone’
Seismographs located at any distance within 105° from the epicentre, recorded the arrival of both P and S-waves.
Seismographs located beyond 145° from epicentre, record the arrival of P-waves, but not that of S-waves.
A zonebetween105° and 145° from epicentre was identified as the shadow zone for both the types of waves.
The entire zone beyond 105° does not receive S-waves.
Shadow zone of S-waves is not only larger in extent but it is also a little over 40% of the earth surface
Types of Earthquakes
Those are mostcommonearthquakes.
These are generated due to sliding of rocks along a fault plane.
Tectonic plates can be displaced in two way
A special class of tectonic earthquake is sometimes recognised as volcanic earthquake.
These are occurred in the areas of active volcanoes.
In the areas of intense mining activity, sometimes the roofs of underground mines collapse causing minor tremors.
Ground shaking may also occur due to the explosion of chemical or nuclear devices
Reservoir induced Earthquakes
The earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced earthquakes
The earthquake events are scaled either according to the magnitude or intensity of the shock.
Magnitudescale is known as the Richterscale.
The magnitude relates to the energy released during the quake.
It expressed in absolute numbers, 0-10.
The intensityscale is named after Mercalli
Intensity scale takes into account the visible damage caused by the event.
The range of intensity scale is from 1-12.
Effects of Earthquake
Differential ground settlement
Land and mud slides
Floods from dam and levee failures
The effect of tsunami would occur only if the epicentre of the tremor is below oceanic waters and the magnitude is sufficiently high.
Tsunamis are waves generated by the tremors and not an earthquake in itself.
Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.
Shield volcanoes are the largestof all the volcanoes on the earth.
The Hawaiian volcanoes are the most famous
It madeofBasalt, a type of lava that is very fluid when erupted
For this reason, these volcanoes are not steep
Basalt is characterised by low–explosive
Upcoming lava moves in the form of a fountain and throws out the cone at the top of the vent and develops into cinder cone
These volcanoes are characterised by eruptions of cooler and more viscous lavas than basalt.
These volcanoes often result in explosive eruptions.
Along with lava, large quantities of pyroclastic material and ashes find their way to the ground.
These are the mostexplosive of the earth’s volcanoes.
They are usually so explosive that when they erupt they tend to collapse on themselves rather than building any tall structure.
The collapsed depressions are called calderas and it form Crater–lake
Their explosiveness indicates that the magma chamber supplying the lava is not only huge but is also in close vicinity.
Flood Basalt Provinces
These volcanoes outpour highly fluid lava that flows for long distances.
There can be a series of flows with some flows attaining thickness ofmore than 50 m.
Individual flows may extend for hundreds of km.
The Deccan Traps from India, presently covering most of the Maharashtra plateau, are a much larger flood basalt province.
Mid-Ocean Ridge Volcanoes
These volcanoes occur in the oceanic areas.
There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins.
The central portion of this ridge experiences frequent eruptions.
Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust).
The lava that cools within the crustal portions assumes intrusive forms.
A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
Batholiths are the cooled portion of magma chambers.
A laccolith is a sheet intrusion that has been injected between two layers of sedimentary rock.
The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base
It can be regarded as the localised source of lava that finds its way to the surface.
The Karnataka plateau is spotted with domal hills of granite rocks.
Lapolith, Phacolith and Sills
As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.
It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called lapolith.
A wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of anticline in folded igneous country.
Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the phacoliths.
The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material. The thinner ones are called sheets while the thick horizontal deposits are called sills.
When the lava makes its way through cracks and the fissures developed in the land
It solidifies almost perpendicular to the ground.
It gets cooled in the same position to develop a wall-like structure.
Such structures are called dykes.
These are the most commonly found intrusive forms in the western Maharashtra area.