The Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the world, the Blue Planet, or by its Latin name, Terra.
Earth formed approximately 4.54 billion years ago by accretion from the solar nebula, and life appeared on its surface within one billion years. The planet is home to millions of species, including humans. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land. The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist. The planet is expected to continue supporting life for another 500 million to 2.3 billion years.
Earth's crust is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.

The United Nations (UN)
is an international organization whose stated aims are to facilitate cooperation in international law, international security, economic development, social progress, and human rights issues. It was founded in 1945 with the signing of the United Nations Charter by 51 countries.

United Nations HQ
New York City
The UN was founded after the end of World War II by the victorious Allied Powers in the hope that it would act to intervene in conflicts between nations and thereby avoid war. The organization's structure still reflects in some ways the circumstances of its founding. The five permanent members of the UN Security Council, each of which has veto power on any UN resolution, are the main victors of World War II or their successor states: the People's Republic of China (formerly the Republic of China), France, Russia (formerly the Soviet Union), the United Kingdom, and the United States.
There are currently 192 United Nations member states, encompassing almost every recognized independent state. From its headquarters in New York City, the UN and its specialized agencies decide on substantive and administrative issues in regular meetings held throughout each year. The organization is divided into five major administrative organs - the General Assembly, the Security Council, the Secretariat, the International Court of Justice, and the Economic and Social Council. Additional bodies deal with the governance of all other UN System agencies, such as the World Health Organization (WHO) and United Nations Children's Fund (UNICEF). The UN's most visible public figure is the Secretary-General, currently Ban Ki-moon of South Korea, who attained the post on 1 January 2007.
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