What makes the Earth unique?
Unlike the other planets of our solar system, life developed into many forms on the Earth after its emergence. Liquid water and oxygen for breathing made this possible. Millions of species of plants and animals thrive today on land and in water. Water covers more than two-thirds of the Earth’s surface. Therefore, the Earth appears blue from the moon or the International Space Station. For this reason, it is also called the ‘blue planet’. Till now, scientists have not discovered life in any other place in the universe, but they believe that one day they will do so.
How was the Earth formed?
The Earth, along with the sun and the remaining planets of our solar system, originated around 4.8 billion years ago from dust particles, which agglomerated gradually. At that time, the young Earth was bombarded by countless meteorites from space. The Earth’s interior was molten and volcanoes erupted constantly. But over millions of years, the Earth’s surface cooled down. Around 3.8 billion years ago, the temperature decreased to about 100°C and the Earth’s crust slowly started becoming solid. At this time the gaseous cover on the Earth was mostly made up of water vapor.
Why did life develop on the Earth?
The origin of life on Earth is a fortunate series of events. The Earth’s distance from the sun was such that its atmosphere and surface cooled down to a moderate level. Liquid water not just water vapor-also formed, and it did not freeze as the sun was not too far away. The cooling of the Earth gave rise to a kind of ‘primordial ocean’. The action of the UV rays of the sun, the lightning flashes produced by storms, and the countless volcanic eruptions gave rise to new complex chemical compounds. About 4 billion years ago, the first molecules appeared, from which the first unicellular organisms were formed.
Where does the oxygen we breathe come from?
Gaseous oxygen was created on the Earth about 3.5 billion years ago. At that time, the UV light of the sun decomposed the water vapor molecules present in the atmosphere and released oxygen and hydrogen. But a major part of the oxygen immediately reacted with other substances, so that it was no longer available in the atmosphere as gas. Oxygen was also produced by the seas, where the ‘blue algae’ carried out photosynthesis (page 59). These bacteria convert sunlight and carbon dioxide into energy. In the process, gaseous oxygen was released as a ‘waste product’, which accumulated in the atmosphere. About one-twentieth (4%) of one billion years ago, about the atmosphere consisted of oxygen.
What would happen if there was no water on the Earth?
Without water, there would be no animals or plants, that carry out photosynthesis and release oxygen, and consequently, the oxygen content in the atmosphere would go down. Moreover, the absence of oceans would have serious consequences as they help to keep the Earth’s climate moderate by storing heat inside them (page 24). Without large water bodies, the temperatures of the sunlit areas and those away from the sunlight would change drastically. The temperature difference between day T and night and between summer and winter would be very large. As a result, hurricanes would be a constant occurrence on the Earth.
