The Earth is a unique planet. It is the only planet in the Solar System that supports life. It supports life because of the following reasons:
- It is located at an optimum distance from the Sun. Thus, it is neither too hot nor too cold.
- Its average temperature is of 17°C, which is suitable for life forms to exist.
- The atmosphere of the Earth consists of gases such as oxygen, nitrogen and carbon dioxide. Ozone present in the atmosphere protects the Earth from the harmful ultraviolet rays of the Sun. The atmosphere also does not allow the heat to escape into space and hence keeps the Earth warm.
- 70% of the Earth is covered with water. The hydrological cycle helps in maintaining the life forms on the Earth.
The Shape of the Planet Earth
Reasons which prove that the Planet Earth is spherical:
- During a lunar eclipse, the shadow of the Earth falls on the surface of the Moon. This shadow is visible as an arc of a circle. Because the shadow always appears spherical, we know that the Earth is spherical.
- The Pole Star can be observed at an angle of 90° in the sky at the North Pole. If we travel southwards, the angle of the Pole Star decreases, and at the Equator, the angle becomes zero. This proves that the path of travel is an arc of a circle.
- Because all the planets and the Moon appear spherical, we can conclude that the Earth too is spherical. The pictures of the Earth taken from space prove that the Earth is a sphere.
Conditions Favouring Life on the Planet Earth
Life on the Earth began because of the existence of the atmosphere, heat, and water.
Biosphere: It is a narrow zone between the lithosphere, hydrosphere, and atmosphere. The upper crust of the Earth is called the biosphere where all forms of plant and animal life are found. Naturally occurring communities characterized by distinctive life forms adapted to broad climatic types are called biomes. Examples: Temperate forests, hot deserts
Ecosystem: The ecosystem is a community of living and non-living organisms which are interdependent in the same area. The relationships between living organisms and their interactions with their living and non-living surroundings constitute an ecosystem. There are numerous ecosystems in the world. Examples: Pond, desert, and river ecosystems The non-living components of an ecosystem are called abiotic components. Examples: Temperature, humidity, wind, soil The living components of the ecosystem are called biotic components. Examples: Plants, animals, humans
The Gaia Theory: The Gaia theory was propounded by the British scientist James Lovelock in 1979. According to this theory, the Earth acts as a single living and self-sustaining organism which can regulate and organize itself.