3rd Class General Knowledge Earth and Universe Notes - Earth and Universe

Notes - Earth and Universe

Category : 3rd Class

Earth and Universe


Interesting Facts

  •             The solar system was formed around 4.6 billion years ago.
  •             The earth is about 4.6 billion year old.
  •             There are five dwarf planets in the solar system named pluto, Ceres Haumea, makemake and eris.


Solar System

  •           The solar system is made up of the Sun, planets, moons/ comets, asteroids, meteoroids, minor planets, dust and gas.
  •           Everything in the solar system orbits or revolves around the Sun. The Sun is so large, that its powerful gravity attracts all the other objects in the solar system towards it.
  •           The Sun is the largest object in the solar system.


Sun: The Sun is in the centre of the solar system. It is huge and made up of extremely hot gases. The Sun is the main source of heat and light for the solar system. It is the nearest star. It is about 150 million kms away from the Earth.


Planets: There are eight planets which revolve around the Sun. Mercury, Venus, Earth and Mars are called inner planets as they are very close to the Sun. Jupiter, Saturn, Uranus and Neptune are called outer planets as they are far away from the sun.


1.            Mercury: Mercury is the smallest and closest planet to the Sun. Though it is nearest to the Sun, Still it is less hotter than Venus. The reason is that the Mercury has no atmosphere to retain Sun's heat on it.


2.            Venus: Venus is the brightest and hottest planet of the solar system. It is also known as the evening star. It can be seen in the sky just after the sun sets.


3.            Earth: This is only planet in the solar system that has life on it. This is the only planet with an atmosphere containing oxygen.


4.            Mars: Mars is the fourth planet and red in colour because of presence of iron minerals on it.


5.            Jupiter: Jupiter is the biggest planet of the solar system. There are strips on the surface of this planet.


6.            Saturn: It is the second largest planet in the solar system with rings along its equator. Rings are made up of dust and ice.


7.            Uranus: Uranus is a giant planet and it is named after the Greek god of sky.


8.            Neptune: Neptune is the last planet in the solar system. Fast wind and storm blow across this planet.



  •          Star is a luminous object that produces light of its own. It is seen as twinkling and shining object in the sky due to the earth's atmosphere.


  •          Group of stars are seen in different parts of the sky forming patterns. These patterns resemble to living or non-living creatures. Such group of stars are called constellations.


  •        Some famous constellations are Ursa Major resembling the shape of a big bear, Ursa Minor resembling a little bear, Orion resembling hunter, etc, are seen in the sky.


  •             There are about 88 constellations seen in the sky.


Layers of Earth

It may seem like the Earth is made up of one big solid rock, but it's really made up of a number of parts. Some of them constantly moving!


You can think of the Earth being made up of a number of layers, sort of like an onion. These layers get more and more dense the closer you get to the center of the Earth See the picture to see the four main layers of the Earth: the crust, mantle, outer core and inner core.




The crust is the thin outer later of the Earth where we live. Well, it looks thin on the picture and is relatively thinner to the other layers, but don't worry, we're not going to fall by accident anytime soon. The crust varies from around 5km thick (in the ocean floor) to around 70km thick (on land where we live called the continental crust). The continental crust is made up of rocks that primarily consists of silica and alumina called the "sial".


Do you know?

  •          The crust is extremely thin when compared to the mantle and occasionally some of the deeper layers of the earth reach the crust when the volcanoes erupt or when earthquakes occur.
  •           Earth's innermost section inner core is believed to be just as hot as the sun?s surface.



The next layer of the Earth is called the mantle. The mantle is much thicker than the crust at almost 3000km deep. It's made up of slightly different silicate rocks with more magnesium and iron.


Outer Core

The Earth's outer core is made up of iron and nickel and is very hot (4400 to 5000+ degrees C). This is so hot that the iron and nickel metals are liquid! The outer core is very important to Earth as it creates something called a magnetic field. The magnetic field, the outer core creates goes way out in to space and makes a protective barrier around the Earth that shields us from the Sun's damaging solar wind.


Inner Core

The Earth's inner core is made up of iron and nickel, just like the outer core, however, the inner core is different. The inner core is so deep within the Earth that it's under immense pressure. So much pressure that even though it is so hot, it is solid. The inner core is the hottest part of the Earth and at over 5000 degrees C, It is as hot as the surface of the Sun.


Features of Earth

1.            Beautiful Earth, home to plants, animals and humans, is the third planet from the Sun. It's the fifth largest planet. Some of the other planets have atmospheres, seasons and even water, but only Earth combines all these elements in just the right way. Earth is the only place in the solar system where life is known to be found.


2.            Most of the places on Earth experience four seasons, caused by the Earth's rotation and tilt. When it's winter in the northern hemisphere, it's summer in the southern hemisphere and vice versa.


3.            Earth is often called the ocean planet. Its surface is 70 percent water. The oceans help regulate the temperature of the planet and influence weather.


4.            The Earth has a molten inner core made of iron and other metals. Under the Earth's crust are plates that slowly move against each other. This movement causes mountains, hills, volcanoes and even earthquakes.


5.            The Earth's atmosphere protects the planet from meteors. They usually burn up before they reach the Earth's surface.


Do You Know?

  •             Earth is the only planet with tectonics plate.
  •             The earth is flattened at the north and the south pole and is found to build at the solor system.

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Notes - Earth and Universe
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