1. Structure of the Earth

Earth is the planet where we live. It is a small part of the universe and the only planet we know to support life. Earth is one of the eight planets that orbit the Sun. It is the third planet from the Sun, after Mercury and Venus, and before Mars. It is about 150 million kilometres from the Sun1.

Earth is a large and massive rock which is spherical in shape. It is far smaller than the gas giants, like Jupiter and Saturn. Jupiter and Saturn are not made of rocks. They are gas giants made mostly of gases and atmosphere.

• Earth has a lot of water. About 70% of its surface is covered by oceans. This is why it is called the 'ocean planet.

• The Earth is at the appropriate distance from the sun making it not too cold and not too hot.

• The Earth's atmosphere has useful gases that trap the Sun’s heat and keep the planet warm enough for living organisms like ourselves to exist. 

• Earth's atmosphere contains nitrogen and sufficient oxygen for us to breathe. 

• Earth is the only planet in the solar system to have one natural satellite, called the moon.

The Earth formed millions of years after the universe began. In fact, our planet is 4.6 billion years old. It was formed from a huge, spinning cloud of gas and dust. The dense centre of the cloud became extremely hot over a period of around 10 million years. This huge centre became the sun. The rest of the particles and objects continued to revolve around the sun1.

Millions of years ago, Earth was formed from gas and dust. As the Earth cooled, heavier materials moved to the center, and lighter ones floated to the top. This formed layers like the crust and core. 

Imagine stirring a pot of soup. The lighter parts float to the top, and the heavier parts sink to the bottom—Earth’s layers formed in a similar way. 

Thus, three major layers formed: the core, the mantle, and the crust1. 

Fig 1.3: Structure of the Earth 

Earth has four layers: crust, mantle, outer core, and inner core. The crust is where we live. The mantle has hot rocks. The outer core is liquid metal, and the inner core is solid and very hot. 

1. The crust

The crust is the layer that we live on. It is made up of slabs of solid rocks and minerals. The Earth’s crust is divided into continental crust (land) and oceanic crust (water). Oceanic crust is thinner as compared to the continental crust. The continental crust is mainly composed of silicon and aluminium while the oceanic crust is mainly composed of silicon and magnesium5.

2. The mantle

The mantle is the thickest layer which lies beneath the earth crust. It is 2800 km deep and is made up of molten rocks. It is hotter than the crust which consists of iron and magnesium-rich solid rocks. The crust and the uppermost part of the mantle are called the lithosphere5. 

3. The outer core

The outer core surrounds the inner core. The high temperature in the outer core keeps all the metals in liquid state. The outer core consists of iron and nickel in liquid form5.

4. The inner core

The inner core is the centre of the earth’s structure and is also made of iron and nickel. The inner core is extremely hot thus making it the hottest layer of all.  The intense pressure and weight of the rocks in the inner core maintains its solid state5. 

Vid 1.2:  Four layers of the Earth 

The interior of the Earth is a complex system  of superheated rocks. All the layers of the earth are unique and affect our planet. Let’s look into the two main effects of the earth's structure. 

1. Tectonic Activity

Between the Earth’s mantle and the crust lies the tectonic plates.  These plates are not fixed in one place. They move constantly due to the heat and pressure from the core. These movements lead to various tectonic activities like earthquakes and volcanic eruptions. The tectonic plates sometimes collide or pull apart from each other. Occasionally these plates slide above and below each other. Such tectonic activities have shaped various landforms over a million years6. 

Fig 1.4: Tectonic Activites

Vid 1.3: How do Tectonic plates move? 

2. Weather and climate patterns

The inside of the Earth affects the weather and climate around us. Since the core is the hottest part, it produces a lot of heat. This heat moves through the Earth, affecting the air and temperature we feel. The Earth's heat helps create weather patterns, like wind and storms. Tectonic activity, or movements inside the Earth, can form tall mountains. These mountains can change how wind moves around the world. When volcanoes erupt, they release gases and tiny particles into the air, which can also change the climate for a while.8 

Fig 1.5: Weather and climate 

Knowing Earth’s structure helps us understand things like earthquakes, volcanoes, and how mountains are formed. It also helps us find important resources like rocks and minerals.10