EARTH

Earth is the third planet from the Sun and the only known astronomical body to harbor life. It has a diameter of about 12,742 km at the equator and a mass of approximately 5.97 × 10^24 kg, making it the largest of the terrestrial planets and the fifth-largest in the Solar System. It completes an orbit around the Sun in about 365.25 days and rotates once every 23 hours 56 minutes. The axial tilt of about 23.5 degrees produces seasonal variation in many regions.

Earth’s surface is 71% covered by liquid water, primarily oceans, with continents and islands comprising the remainder. The interior consists of a crust, a silicate mantle, and a core divided into a liquid outer part and a solid inner part. The movement of tectonic plates drives geological activity, including earthquakes and volcanism. The atmosphere is mostly nitrogen (about 78%) and oxygen (about 21%), with carbon dioxide and other gases making up the rest. The planet’s magnetic field helps shield the atmosphere from solar wind.

Earth hosts a diverse biosphere, from microorganisms to plants and animals, sustained by a global water cycle and energy from the Sun. Life has left widespread signatures in rocks and the atmosphere, and humans are a major influence on many ecosystems.

Earth formed about 4.54 billion years ago by accretion within the solar nebula. The Moon, its largest natural satellite, formed soon after and has influenced Earth’s tides and rotation. Modern exploration has increased knowledge about Earth’s geology, climate, and habitability, while human activity raises concerns about climate change and biodiversity loss.