Earth is the third planet from the , the densest planet in the , the largest of the Solar System's four, and the only known to harbor .
According to and other sources of evidence, Earth formed about 4.54 billion years ago. Earth interacts with other objects in space, especially the Sun and the. During one orbit around the Sun, Earth rotates about its own axis 366.26 times, creating 365.26 or one Earth's axis of rotation is tilted 23.4° away from the perpendicular of its , producing seasonal variations on the planet's surface within a period of one (365.24 solar days)The Moon, Earth's only permanent , by its gravitational relationship with Earth, causes ocean tides, stabilizes the orientation of Earth's rotational axis, and gradually slows Earth's rotational rate.
Earth's is divided into several rigid 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 . The majority of Earth's are covered in ice, including the 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 , and a convecting that drives plate tectonics.
Within its first billion years, life appeared in Earth's oceans, and began to affect the and surface, leading to the proliferation of and . Since then, the combination of Earth's distance from the Sun, physical properties, and have allowed life to evolve and today thrive. The earliest undisputed life on Earth arose at least 3.5 billion years ago. Earlier physical evidence of life includes in 3.7 billion-year-old discovered in southwestern , as well as "remains of " found in 4.1 billion-year-old rocks in Except when interrupted by , Earth's has continually expanded Although scholars estimate that over 99% of all species of life (over five billion)that ever lived on Earth are today there are an estimated 10–14 million species still in existence, of which about 1.2 million have been documented and over 86% have not yet been described.More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. In July 2016, scientists reported identifying a set of 355 from the (LUCA) of all living on Earth.Over 7.3 billion live on Earth and depend on its and for their survival. Earth's human population is divided among about 200 sovereign that interact through diplomacy, conflict, travel, trade, and communication media.