Earth

- Earth

Earth is the third planet in the solar system and the only known habitable place in the universe where life originated. While water can be found in large quantities throughout the solar system, only Earth maintains liquid surface water. 

Liquid water makes up most of the Earth's surface, with 70.8% of the Earth's surface area occupied by oceans, making the planet an oceanic world, with large ice caps currently surrounding the planet's polar regions. Made up of continents and islands, the landmass covers 29.2% of the Earth's surface, and is extensively covered in vegetation, with lakes and rivers dwarfed by polar ice caps. 

Earth's surface rests on the crust of several slow-moving tectonic plates that interact to create mountains, volcanoes and earthquakes. The magnetic field generated by Earth's liquid outer core shapes the planet's magnetosphere, deflecting the destructive solar wind. 

Earth's atmosphere is mainly composed of nitrogen and oxygen. Greenhouse gases in the atmosphere, such as carbon dioxide (CO2), trap some of the sun's energy near the surface. Water vapor is widespread in the atmosphere, forming clouds that cover most of the planet. Tropical regions receive more solar energy than polar regions and redistribute it through atmospheric and oceanic circulation. 

A region's climate is affected not only by latitude, but also by altitude and proximity to moderate oceans. Severe weather such as tropical cyclones, thunderstorms, and heat waves occur from time to time in most areas, which have a great impact on life. 

The Earth is an ellipsoid with a circumference of approximately 40,000 km. It is the densest planet in the solar system. Of the four rocky planets, it is the largest and most massive. 

The earth is about eight light minutes from the sun and revolves around the sun, taking one year (about 365.25 days) to complete one revolution. The Earth takes slightly less than a day (about 23 hours and 56 minutes) to rotate on its axis. 

The Earth's axis of rotation is tilted relative to the perpendicular to the plane of its orbit around the Sun, giving rise to the seasons. The Earth is orbited by a permanent natural satellite, the Moon, which orbits the Earth 384,400 km (1.28 light-seconds) and is about one-quarter the width of the Earth. Tidally locked, the Moon always faces the Earth with the same face, which creates tides, stabilizes the Earth's axis, and gradually slows down its rotation. 

Like most other bodies in the solar system, Earth formed 4.5 billion years ago from gases from the early days of the solar system. During the first billion years of Earth's history, oceans formed and life developed in them. 

Life spread across the globe and began to affect Earth's atmosphere and surface, leading to the Great Oxygenation Event 2 billion years ago. Humans emerged 300,000 years ago and today number 8 billion. The survival of human beings depends on the earth's biosphere and natural resources, but it also has an increasing impact on the earth's environment. 

Humanity's current impact on Earth's climate and biosphere is unsustainable, threatening the livelihoods of humans and many other life forms, and causing widespread extinctions.