The study of the earth’s interior is that the subject of Geology, Since, the inside a part of the world isn’t visible directly, knowledge about it’s gathered through indirect means. the world as an entire has been divided into 3 broad zones – Crust, Mantle and Core.
The Crust
The Average thickness of this upper most layer of the world is about 30 km. the typical density of the upper class is 2.8 which of the lower crust is 3.0. This difference in density is believed to flow from to the pressure. This discontinuity in density between upper class and lower crust is understood as ‘conrad discontinuity’. Silica and Allumunium are the most constituent elements of the crust. Therefore, it’s also referred to as the SIAL.
The Mantle
At the lower end of the crust the speed of the seismic waves increases suddenly and reaches upto 7.9 to 8.1 km/sec. This results into a discontinuity between the layer and therefore the lower crust, which shows a change within the density of the rocks. This discontinuity was discovered in 1909 by a Russian scientist A. Mohorvicie, therefore, it’s named after him as ‘Mono-discontinuity’. The mantle extends UPPER MANTLE” upto a depth of about 2900 km from the Moho-discontinuity,. Silica and Magnesium are the main constituting elements of this layer, hence it’s also called SIMA.
Between 100 km to 200 km depth of the layer , the speed of the seismic waves is bogged down to 7.8 km/sec. Therefore, this zone is is understood because the ‘Zone of Low Velocity’. The discontinuity in density between layer and layer is understood as Repetti discontinuity.
The Core
At the lower end of the layer the speed of the P waves suddenly increases to 13.6 km/sec. This shows as sudden change within the density of the rocks resulting into a kind of discontinuity, referred to as ‘Weicher Gutenber Dscontinuity’. it’s divided into two parts Outer core and inner core. S waves cannot penetrate into the outer core. The density of the core is quite the double of the density of the mantle. within the inner core where the density is at its maximum, the speed of the P waves is 11.23 km/sec thanks to its relatively liquid or semi-liquid state due to excessive temperature but due to an excessive amount of pressure it’s in semi-liquid or plastic state. It’s main constituens are nickel and iron, so it’s also referred to as NIFE.
Motions of the world
The Earth has two sorts of motions:
1. Rotational Motion
2. Revolution or orbital rotation
Rotation: the world rotates on its axis, from west to east sort of a top. This motion is named Rotation of the world .
Revolution: While rotating on its axis, the world also goes round the sun in an elliptical path and completes one round in three hundred and sixty five days and 6 hours. The elliptical path traced by the world is named its orbit. This motion of the world is named revolution.
Earth’s Perihelion and Aphelion
Perihelion: When the world is at the minimum distance from the sun, while in orbit, this position is understood as perihelion. the world is closest to the Sun, or at the perihelion, about 2 weeks after the December Solstice, when it’s winter within the hemisphere . When earth is at perihelion, it’s about 147 million km (91 million miles) from the Sun. Perihelion always occurs near January 4th
When the earth is furthest faraway from the Sun, it’s at aphelion. The words “aphelion” and “perihelion” come from the Greek language. In Greek, “helios” model , “peri” means near, and “apo” means faraway from . Aphelion lands near the 4th of July. the world is farthest faraway from the Sun, at the aphelion point, 2 weeks after the June Solstice, when the hemisphere is enjoying warm summer months.
Perigee and Apogee
Like the Earth’s orbit round the Sun, the Moon’s path round the Earth is elliptical. the purpose within the Moon’s orbit that’s closest to the world is named the Perigee and therefore the point farthest from the world is understood because the Apogee.
Change in Seasons
The earth moves not only on its axis but also in its orbit round the sun. Therefore, the world changes its position continuously with reference to the sun. There are four major positions of the world , while it revolves round the sun.
Position on 21st June: during this position the sun shines perpendicularly over the Tropic of Cancer. This position in called the June 21 . it’s the time of summer season within the hemisphere , while within the hemisphere , it’s winter season. The day within the hemisphere is longest on 21st June.
Position on 22nd December: during this position the Sun shines perpendicularly over the Tropic of Capricorn. This position is named solstice . During this era , days are long and nights are short within the hemisphere . This positions marks the summers within the hemisphere and winters within the hemisphere .
Positions on 21st March and 23rd September: In these two positions the Sun shines directly overhead on the Equator. Therefore, half a part of all latitudes receives the sun-light at these times. Hence, everywhere, the duration of day and night is equal.. Seasons also are similar in both the hemispheres. These two positions are mentioned as Equinoxes. 21st March is named Spring or Vernal Equinox whereas 23rd September is named Autumn Equinox.
Eclipses
Both the world and therefore the Moon get light form the Sun. just one a part of the Moon are often seen from the world due to equal rotational speed of both the world and therefore the Moon. Illuminated face of the Moon is seen on the world once a month on the complete Moon. On the new phase of the moon the Moon isn’t seen in the least because on tonight the completely dark Moon faces the world .
Lunar Eclipse: When the world comes in between Sun and therefore the Moon, the sunshine of the Sun isn’t ready to reach the Moon, rather, the shadow of the world falls on the moon. this is often called the eclipse . eclipse always occurs on a full-of-the-moon .
Solar Eclipse: When the Moon comes in between the Sun and therefore the Earth, the sunshine of the Sun is interrupted and shadow of the Moon falls on the world . this is often called the eclipse , which occurs on new phase of the moon day.
Night and day
Night and day happen because Earth rotates, or makes one complete turn, every 24 hours. also as traveling in an orbit round the Sun, planet Earth spins around its axis, an imaginary line browsing the North and South Poles. this suggests that at anybody time, half Earth is facing the Sun and has daytime, while the opposite half faces faraway from the Sun, so it’s night.
Seasons of Earth
Earth has seasons because it’s titled at an angle. this suggests that because it orbits round the Sun different parts are titled towards the Sun. when the hemisphere or top half the world , points to the Sun, this area gets summer. At an equivalent time, the hemisphere , or bottom half the world , is pointing faraway from the Sun and this area experiences its winter.
