Earth

Earth is the third planet from the Sun. It is also the only known planet to harbour life. It is where everyone who have ever existed has lived, but that might not be the case forever. Earth is also known as the blue planet or the blue marble because 70% of its surface is covered in oceans. Not only that, but while large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. Without the Sun no life on Earth could exist. It is our only planet for a good while, so we must look after it. In the past few years, humans have created a lot of pollution of all kinds on Earth and the crisis has already started. The temperatures on Earth have raised by 1°C in the past 50 years and on track to raise by 2°C by 2050.

Earth's crust is formed of several slowly moving tectonic plates, interacting to produce mountain ranges, volcanoes, and earthquakes. Earth's liquid outer core generates the magnetic field that shapes Earth's magnetosphere, deflecting destructive solar winds. The planet's atmosphere consists mostly of nitrogen and oxygen. Greenhouse gases in the atmosphere like carbon dioxide (CO2) trap a part of the energy from the Sun close to the surface. Water vapour is widely present in the atmosphere and forms clouds that cover most of the planet. More solar energy is received by tropical regions than polar regions and is redistributed by atmospheric and ocean circulation. A region's climate is governed by latitude, but also by elevation and proximity to moderating oceans. In most areas, severe weather, such as tropical cyclones, thunderstorms, and heatwaves, occurs and greatly impacts life.

Earth is an ellipsoid with a circumference of about 40,000 km. It is the densest planet in the Solar System. Of the four rocky planets, it is the largest and most massive. Earth is about 150,000,000Km (eight light minutes) away from the Sun as it orbits it every year (about 365.25 days). Earth rotates around its own axis in slightly less than a day (3 hours, 56 minutes, 4.1 seconds). Its axis of rotation is tilted with respect to its orbital plane around the Sun by 23.439°, producing seasons. Earth is orbited by one permanent natural satellite, the Moon, which orbits Earth at 380,000 km (1.3 light seconds) and is roughly a quarter as wide as Earth. The Moon always faces the Earth with the same side through tidal locking and causes tides, stabilizes Earth's axis, and gradually slows its rotation.

Earth, like most other Solar System bodies, formed 4.5 billion years ago from gas of the early Solar System. During the first billion years of Earth's history, the ocean formed and then life developed within it. Life spread globally and began to affect Earth's atmosphere and surface, leading to the Great Oxidation Event two billion years ago. Humans emerged 300,000 years ago, and have reached a population of over 8 billion today. Humans depend on Earth's biosphere and natural resources for their survival.

## Carl Sagan's Quote 'Pale Blue Dot'

“Look again at that dot. That's here. That's home. That's us. On it, everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there-on a mote of dust suspended in a sunbeam.“