Earth

Earth is the only planet in our Solar System where life exists. Approximately 4.5 billion years ago, Earth formed from the particles left over from the creation of our Sun. Gravity pulled swirling gas and dust in together to form the Earth. It is the third planet in our Solar System.


29% surface on Earth is land ( i.e continents and islands ) and the rest 71% is water mostly oceans but also lakes, rivers and other fresh water bodies. Out of this 71% water, 97% is saline water(water in oceans) and the availability of freshwater is only 3%. Earth’s polar region is covered with ice.

Earth’s atmosphere contains 78% nitrogen, 21% oxygen and 1% other gases such as carbon dioxide, argon and neon. The atmosphere acts as a shield and protect us from the harmful radiation coming from the Sun. It also protects us from meteoroids which burn up in the atmosphere before they can hit the surface.

Earth is the only planet that was not named after a Greek or Roman god. Its alternative names are Gaia, Gaea, Terra, Tellus, The World, The Globe.

The journey of life on Earth started in oceans. The earliest forms of life were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. These microbes are known as Prokaryotes that fed on carbon compounds that were accumulating in Earth’s early oceans. Slowly, many other organisms evolved that used the Sun’s energy, along with compounds such as sulfides, to generate their own energy.


Earth is composed of four main layers.
The inner core is a solid sphere made of iron and nickel metals about 759 miles (1,221 kilometers) in radius. The temperature there is as high as 9,800 degrees Fahrenheit (5,400 degrees Celsius). Surrounding the inner core is the outer core. This layer is about 1,400 miles (2,300 kilometers) thick, made of iron and nickel fluids.In between the outer core and crust is the mantle, the thickest layer. This hot, viscous mixture of molten rock is about 1,800 miles (2,900 kilometers) thick and has the consistency of caramel. The outermost layer, Earth’s crust, goes about 19 miles (30 kilometers) deep on average on land. At the bottom of the ocean, the crust is thinner and extends about 3 miles (5 kilometers) from the sea floor to the top of the mantle.

Earth doesn’t take 24 hours to rotate on its axis
It actually takes 23 hours, 56 minutes and 4 seconds to completely rotate around it’s axis. Also known as sidereal day. Earth’s rotation is slowing slightly with time. Thus, a day was shorter in the past. This is due to the tidal effects the Moon has on Earth’s rotation. Analysis of historical astronomical records shows a slowing trend that the length of a day increased about 2.3 milliseconds per century since the 8th century BCE.

Earth has only one moon. Without the moon, a day on earth would only last six to twelve hours. There could be more than a thousand days in one year. That’s because the Earth’s rotation slows down over time thanks to the gravitational force or pull of the moon and without it days would go by in a blink.