May 22, 2022
Earth is the third planet from the Sun which is the densest and fifth largest of the eight planets in the Solar System. Earth is also the largest of the four terrestrial planets in the Solar System. Earth is sometimes referred to as the world or the Blue Planet. Earth formed about 4.54 billion years ago, and life appeared on its surface at least 3.5 billion years ago. Earth's biosphere then slowly changes the atmosphere and other basic physical conditions, enabling the proliferation of organisms and the formation of the ozone layer, which together with Earth's magnetic field blocks harmful solar radiation and allows microscopic living things to reproduce safely on land. The physical properties, geological history, and orbit of the Earth allow life to continue to exist. Earth's lithosphere is divided into rigid segments, or tectonic plates, which undergo movement across the Earth's surface over millions of years. More than 70% of the Earth's surface is covered by water, and the rest is made up of continents and islands which have many lakes and other water sources that contribute to the formation of the hydrosphere. Earth's poles are mostly covered in ice; solid ice in Antarctica and sea ice in polar ice packs. The Earth's interior remains active, with the inner core composed of solid iron, the outer core being a fluid that creates a magnetic field, and a thick, relatively dense layer in the mantle. Earth interacts gravitationally with other objects in space, especially the Sun and Moon. When around the Sun in one orbit, the Earth rotates on its axis 366.26 times, which creates 365.26 solar days or one sidereal year. The Earth's rotation on its axis is tilted 23.4° from the parallel plane of the orbit, which causes the difference in the seasons on the Earth's surface with a period of one tropical year (365.24 solar days). The Moon is Earth's only natural satellite, which began orbiting Earth about 4.53 billion years ago. The gravitational interaction between the Moon and Earth stimulates tides, stabilizes the tilt of the axis, and gradually slows the Earth's rotation. Earth is home to millions of living things, including humans. The Earth's mineral resources and other biosphere products contribute to providing resources to support the global human population. The territory of the Earth inhabited by humans is grouped into 200 sovereign states, which interact with each other through diplomacy, travel, trade, and military action.