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] (Greek: Γαῖα Gaia;[n 6] Latin: Terra) is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets.
According to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago.Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. During one orbit around the Sun, Earth rotates about its axis over 365 times; thus, an Earth year is about 365.26 days long.[n 7] Earth's axis of rotation is tilted, producing seasonal variations on the planet's surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earth's orientation on its axis, and gradually slows its rotation.
Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water, mostly by its oceans. The remaining 29% is land consisting of continents and islands that together have 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 Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species 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 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures; politically, the world has about 200 sovereign states.