Major Domains of the Earth: Lithosphere, Hydrosphere, Atmosphere and Biosphere

The Earth’s surface is where rock, water, air and life meet. Geographers call these four parts domains.

The Class 6 geography book names them the lithosphere, the hydrosphere, the atmosphere and the biosphere.

1.1 What is the lithosphere?

The lithosphere is the solid part of the Earth on which we live. It holds the rocks of the Earth’s crust and a thin layer of soil.

The soil holds the nutrients that plants and other living things need.

1.2 What is the hydrosphere?

The hydrosphere is all the water of the Earth. It includes ice, liquid water and water vapour.

Rivers, lakes, seas, oceans and groundwater all belong to it.

1.3 What is the atmosphere?

The atmosphere is the layer of gases around the Earth.

It gives us air to breathe. Its upper layers also take in harmful rays from the Sun.

1.4 What is the biosphere?

The biosphere is the narrow zone where land, water and air meet. All life on the planet lives in this zone.

National Geographic Education adds that it reaches from the deepest tree roots to ocean trenches and high mountaintops.

The land is the part of the lithosphere we can see. It is split into big blocks called continents.

2.1 How many continents are there?

There are seven continents. They are Asia, Europe, Africa, North America, South America, Australia and Antarctica.

Asia is the largest. The school book says it covers about one-third of the total land area. Australia is the smallest.

A newer Class 6 book adds a note. Counts of continents vary between four and seven. Seven is the list most people use.

2.2 Where are the borders between them?

The Ural Mountains separate Asia from Europe. Together the two form one landmass called Eurasia.

North America and South America are joined by a narrow strip of land. It is the Isthmus of Panama.

2.3 What does the lithosphere look like up close?

Rock and soil show up in mountains, plateaus and canyons. In the Grand Canyon, the river has cut down through many layers of rock.

About 71% of the Earth’s surface is covered with water. About 29% is land. That is why the Earth is called the Blue Planet.

Older books say “more than 71 per cent”. NASA says “about 71%”. NOAA says “more than 70 percent”. Use “about 71%” in answers.

3.1 Where is the water kept?

About 97% of the Earth’s water is in the oceans. The rest is fresh water, mostly in ice caps and glaciers and in groundwater.

The USGS gives a finer split. It puts 96.5% in oceans, seas and bays, and 1.74% in ice caps, glaciers and permanent snow.

NCERT’s text says “more than 97%”, but its figure says 97.5%. All of these agree that nearly all water is salty ocean water.

3.2 How many oceans are there?

There are five oceans. In order of size they are the Pacific, Atlantic, Indian, Southern and Arctic.

NOAA says most countries now treat the Southern Ocean as the fifth. It lies around Antarctica.

The Bering Strait joins the Arctic Ocean to the Pacific.

3.3 How big is the Pacific Ocean?

The Pacific is the largest ocean.

NOAA gives its area as about 155 million km². The school book says it spreads over about one-third of the Earth.

NOAA also says all the continents could fit in the Pacific basin.

Dry air is mostly two gases. NASA says it is 78% nitrogen and 21% oxygen. The last 1% is argon, carbon dioxide and other gases.

So nitrogen and oxygen together make up about 99% of the air. NOAA’s finer numbers agree.

4.1 What are the five layers?

From the ground up, the layers are the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.

The troposphere is the lowest layer. Weather and rain happen here. NASA says it holds about 99% of the water vapour.

4.2 Why does the stratosphere matter?

The stratosphere sits above the troposphere. EPA says it extends from about 10 km to about 50 km. NASA says it lies between about 12 and 50 km. NASA calls it the home of Earth’s ozone layer. EPA says most atmospheric ozone is concentrated in it.

Ozone takes in harmful ultraviolet rays from the Sun. That heat is why the air gets warmer as you go higher in the stratosphere.

In the troposphere below, the air gets colder with height. The school chapter does not mention ozone, but exams often ask about it.

The biosphere is where the other three domains overlap. A plant needs soil from the lithosphere. It needs water from the hydrosphere. It also needs gases from the atmosphere.

A fish lives in water. Its home is the part of the biosphere where water, land and life meet.

So the biosphere is a thin overlapping zone, not a fourth separate layer.

The highest point on land is Mount Everest. The deepest known point of the oceans is in the Mariana Trench.

6.1 How high is Mount Everest?

NCERT gives 8,848 m above sea level. A joint Nepal-China survey announced in December 2020 gave 8,848.86 m.

Both numbers appear in books. Write 8,848 m if the question follows the textbook. The 2020 survey gave the newer figure.

Tenzing Norgay and Edmund Hillary first climbed it on 29 May 1953. Bachendri Pal became the first Indian woman to reach the summit on 23 May 1984.

6.2 How deep is the Mariana Trench?

The Mariana Trench lies in the western Pacific, near the Mariana Islands. Its deepest part is called Challenger Deep.

NCERT gives the depth as 11,022 m. NOAA gives about 10,935 m. Guinness World Records gives 10,935 m, give or take 6 m.

Measurements differ by method and year. Always read which source a question uses.

Even the lower figure is deeper than Everest is tall. National Geographic says Everest would not even reach the surface if it sat in the trench.

Antarctica has no permanent human settlements, but India runs research stations there. NCERT’s old book names Maitri and Dakshin Gangotri.

That is out of date. India’s first station, Dakshin Gangotri, was decommissioned on 25 February 1990. It became a supply base.

A PIB release of August 2013 says India then had two research stations in Antarctica. They were Maitri and Bharati.

If a question quotes the textbook, check which source it follows.

Several traps come up often.

8.1 Which wrong statements should you spot?

• Water share: 71% is the share of the Earth’s surface covered by water. It is not the share of water kept in the hydrosphere.
• Where the water is: about 97% of all water is in the oceans.
• Depth and height: NCERT says 11,022 m and 8,848 m. NOAA says about 10,935 m for Challenger Deep. A 2020 survey says 8,848.86 m for Everest.
• Stations: a PIB release of August 2013 listed Maitri and Bharati as India’s two stations. Dakshin Gangotri closed in 1990.
• Ozone: it lies in the stratosphere, not the troposphere.