Earth, the third planet from the Sun, is unique in the Universe as it is currently the only planet known to support life. It has a single natural satellite, the Moon, and is the fifth largest planet in the Solar System.
Earth's distance from the Sun is thought to be one of the key reasons why it is home to widespread life. Our planet occupies what scientists sometimes call the Goldilocks zone. Its distance from our star means it is neither too hot, nor too cold to support liquid water - thought to be a key ingredient for life. Astronomers are searching for rocky planets like ours in the Goldilocks zones of other stars.
BBC Earth has exciting videos about volcanoes, earthquakes and more.
Photo: The Earth rising behind the Moon taken by the Apollo 16 crew (NASA)
Our life-filled home is unique in the Universe (so far).
Scientists tell the story of Martian meteorite ALH84001's discovery.
Each year scientists hunt for meteorites in Antarctica because the ice and snow make it easier to spot dark space rocks. In 1984, the team found a special Martian meteorite that came to be known as ALH840001. In the 1990s a NASA team announced that they had found tiny fossils in this rock. Many in the scientific community are critical of this finding.
Rocks from Mars can make the long journey to Earth.
Asteroids and comets have struck Mars with so much force that rocks from the planet's surface were ejected into space. Some of those rocks have made the journey to Earth, falling through the atmosphere to become meteorite deposits.
The early Solar System was a shooting gallery.
Professor Brian Cox explains how the orbiting gas giants may have caused an enormous asteroid and comet bombardment in the inner Solar System 3.6 billion years ago. Earth and the other planets were peppered by asteroids and comets.
Brian Cox looks at what makes the two planets so different.
Professor Brian Cox looks at how greenhouse gases made Earth and Venus so different today.
If life can exist in solid ice on Earth, what about Europa?
Professor Brian Cox goes to caves in Iceland to find microbial life that survives in solid ice. Astrobiologists theorise that if life can live in solid ice on Earth, it may be able to survive on Jupiter's icy moon Europa
Earth (otherwise known as the world,[n 5] in Greek: Γαῖα Gaia,[n 6] or in Latin: Terra) is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.
According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earth gravitationally interacts with other objects in space, especially the Sun and the Moon. During one orbit around the Sun, Earth rotates about its axis 366.26 times, creating 365.26 solar days or one sidereal year.[n 7] Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface within a period of one tropical year (365.24 solar days). The Moon is the Earth's only permanent natural satellite; their gravitational interaction causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.
Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. 71% of Earth's surface is covered with water. The remaining 29% is land mass—consisting of continents and islands—that together has many lakes, rivers, and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, and a convecting mantle that drives plate tectonics.
Within the first billion years of Earth's history, life appeared in the oceans and began to affect the atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive. Life arose on Earth by 3.5 billion years ago, though some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. In the history of the Earth, biodiversity has gone through long durations of expansion but has been occasionally punctuated by mass extinction events. Over 99% of all species of life that ever lived on Earth are extinct. Estimates of the number of species on Earth today vary widely; most species have not been described. Over 7.3 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humanity has developed diverse societies and cultures; politically, the world is divided into about 200 sovereign states.