Our Home: Earth, a Unique Life Sustaining Planet

Class 08 Science

While there are billions of planets in the universe, Earth is the only one where life, as we know today, exists and thrives in all its forms.

Our solar system has eight planets that go around the Sun in nearly circular orbits. In order of their increasing distance from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Out of all these planets, Mercury, Venus, Earth, and Mars, are relatively small and rocky planets, while Jupiter, Saturn, Uranus, and Neptune are large planets, mostly made of gases.

All planets in the solar system get their energy from the Sun. Thus, when a planet is close to the Sun, it would be very hot. As we move away from the Sun, planets should get colder. This is generally correct, except that Venus, the second planet from the Sun has the highest average temperature and is the hottest planet.

Venus is the hottest planet not because it is the closest to the Sun, but because its thick atmosphere traps heat. The air on Venus is almost entirely made up of carbon dioxide gas, which does not let the heat escape. This is called the greenhouse effect, and it makes Venus even hotter than Mercury, which is relatively closer to the Sun.

On the Earth also, gases like carbon dioxide in the atmosphere trap heat by absorbing the radiation given off by the Earth, after it gets warmed by the Sun. Thus, greenhouse effect plays an important role in maintaining just the right temperature on Earth.

Position of the Earth

The most important reason why the Earth can support life is its distance from the Sun. It is just at the right distance, where the temperature allows water to exist in a liquid form. If the Earth were closer to the Sun, it would be too hot and all the water would evaporate; if it were farther away, it would be too cold, and all the water would freeze. In such extreme conditions, it would have been impossible for most life forms - especially plants, animals, and humans - to grow and thrive on Earth.

Although some microbes, like certain bacteria, can survive in frozen environments, liquid water is essential for life to evolve. Earth’s distance from the Sun allows water to remain mostly in liquid form, which is essential for the development and sustenance of life in all its form. The range of distances from the Sun (or another star) over which water remains liquid is called the habitable zone, or sometimes also called the ‘Goldilocks zone’.

Size of the Earth

In our solar system, the orbits of most planets, including the Earth are almost circular. This keeps the amount of sunlight and heat nearly steady throughout the year, preventing extreme summers and winters at most places. However, moderate temperature due to the right distance from the Sun isn’t the only factor that makes the Earth habitable.

The planet is also the right size to support an atmosphere. The atmosphere is the layer of gases that surrounds the Earth, and it plays a major role in sustaining life. Earth’s gravity pulls objects towards it. If Earth were much smaller (but with the same average density), its gravity would have been too weak to hold on to the gases in our atmosphere, and they would have escaped into space. On Mars, the atmosphere is 100 times thinner than on Earth, and Mercury has no atmosphere at all.

On the other hand, if the planet was too large, and gravity was much stronger, it would perhaps pull us down. Due to the right size of the Earth, it is able to support atmosphere which is essential for life.

The presence of oxygen in the Earth’s atmosphere allows us to breathe, and is needed by almost all forms of life on Earth. But oxygen has another important role. Some of the oxygen in our atmosphere, gets converted to another form called ozone (a three-atom oxygen molecule), and forms an important part of the atmosphere called the ozone layer. This layer acts like a shield, blocking harmful ultraviolet (UV) rays from the Sun that can damage living cells.

Magnetic Field of the Earth

A freely suspended magnet always settles in a fixed direction. This is because the Earth itself behaves like a giant magnet.

Earth is constantly hit by tiny, high-energy particles that come from space. Some come from far across the universe and are called cosmic rays. Other particles come from the Sun and are called the solar wind. These particles can be harmful as they can damage the atmosphere, reduce the ozone layer, and let in more harmful UV rays, which can affect life on Earth.

The Earth’s magnetic field acts like a protective shield. It pushes many of these harmful particles away from the Earth, keeping our atmosphere, and hence life on our planet safe.

Air, Water, and Sunlight

The atmosphere contains oxygen, which humans, animals, and plants use for respiration. In the presence of sunlight, plants take carbon dioxide from the air and water from the soil to prepare food by photosynthesis. In the process, oxygen is released, which is needed for respiration.

Radiation from the Sun heats the Earth. Some of this heat is trapped by the atmosphere due to the greenhouse effect. This effect though mild, keeps the temperature just high enough for water to remain in the liquid state. So the greenhouse effect helps keep the Earth warm.

Water is essential for life. It covers about 70 per cent of the Earth’s surface and is found in ponds, lakes, rivers, springs, seas, oceans, and groundwater. All this water forms the hydrosphere. Water transports nutrients from soil to leaves in plants. In animals, it regulates body temperature, aids digestion, and ensures hydration, all essential for health and life.

The hydrosphere is home to millions of life forms, from tiny planktons to giant whales. Oceans, lakes, and rivers provide rich environments for aquatic life. Freshwater is also needed to grow crops and support people around the world.

Water vapour in the air forms clouds and brings rain or snow. This refills rivers, lakes, and underground water. Rainfall affects the kinds of plants and animals that can live in a place. Moving air also shapes weather and rainfall - which influence farming, water supply, and life on land.

Soil, Rocks, and Minerals

The Earth’s crust is made of rocks, soil, and minerals. It provides almost everything life needs to grow and survive. From soil that helps plants grow to minerals that give us salt, coal, oil, and metals like iron and copper - this outer layer support both ecosystems and human life. The solid parts of the Earth, including materials like rocks, soils, and minerals are known as the geosphere.

There are various types of landforms, rocks, soils, etc., on Earth. This variety along with the processes that shape and alter them is called geodiversity. It helps create unique habitats where different types of life can thrive.

Plants, Animals, and Microorganisms

The Earth is full of life - from trees, shrubs, herbs, to animals, insects, and tiny organisms invisible to the naked eye. All living beings, along with the places where they live, make up the biosphere. This includes land, water, and air, where life interacts with its surroundings to survive and grow.

Living beings depend on one another and their environment. Plants make food through photosynthesis, animals eat plants or other animals, and decomposers break down dead matter and return nutrients to the soil. Nature works together as a system to support life.