Earth is the third planet from the Sun and the largest of the four terrestrial planets in the Solar System. It is the only astronomical body currently known to support life. Earth has extensive liquid water on its surface, a dynamic atmosphere, a protective magnetic field, and a complex system of interacting geological, chemical, and biological processes.
Earth formed approximately 4.54 billion years ago from material in the solar nebula, the rotating cloud of gas and dust from which the Solar System developed. During its early history, Earth was subjected to frequent impacts by smaller bodies and experienced extensive volcanic activity. A major impact early in its history is thought to have produced the Moon.
As Earth cooled, a solid crust formed over a hotter interior. Water accumulated on the surface through a combination of volcanic outgassing, condensation, and material delivered by impacts. The development of stable oceans provided environments in which early forms of life could emerge.
The geological history of Earth is divided into eons, eras, periods, and other intervals. Major events in Earth's history include the development of the first known life, the rise of oxygen in the atmosphere, the diversification of complex organisms, the evolution of land plants and animals, and the emergence of humans.
Earth is approximately 12,742 kilometres in diameter and has a mass of about 5.97 × 1024 kilograms. It is not a perfect sphere; its rotation causes it to bulge slightly at the equator and flatten toward the poles.
The planet consists of several major layers. The outermost solid layer is the crust, which is divided into continental and oceanic crust. Beneath the crust is the mantle, a thick layer of hot rock that behaves plastically over geological timescales. At the center of Earth is the core, which is primarily composed of iron and nickel. The core has a liquid outer portion and a solid inner portion.
Earth's internal heat comes partly from the energy remaining from its formation and partly from the radioactive decay of elements within the planet. This heat drives convection in the mantle and contributes to plate tectonics and volcanic activity.
Earth's surface is divided between land and ocean. The oceans cover approximately 71 percent of the planet's surface, while continents and islands account for most of the remaining area.
The major continents are Africa, Antarctica, Asia, Europe, North America, South America, and Australia. The boundaries and shapes of continents have changed throughout geological history as a result of plate tectonic activity.
Earth contains a wide variety of physical features, including mountains, valleys, plains, plateaus, deserts, forests, glaciers, rivers, lakes, and ocean trenches. The highest point above sea level is Mount Everest, while the deepest known point on Earth's ocean floor is the Challenger Deep in the Mariana Trench.
Earth is surrounded by an atmosphere consisting primarily of nitrogen and oxygen, with smaller amounts of argon, carbon dioxide, water vapour, and other gases. The atmosphere is held around the planet by gravity.
The atmosphere is divided into several layers, including the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Most weather occurs in the troposphere. The stratosphere contains the ozone layer, which absorbs much of the Sun's harmful ultraviolet radiation.
Earth's atmosphere plays an important role in regulating the planet's temperature. Atmospheric gases absorb and emit thermal radiation, producing the natural greenhouse effect. Without this effect, Earth's average surface temperature would be substantially lower.
Earth has a diverse climate system influenced by solar energy, atmospheric circulation, ocean currents, geography, and the composition of the atmosphere. Climate varies considerably between different regions and changes over geological and historical timescales.
The planet experiences several broad climate zones, including tropical, dry, temperate, continental, and polar climates. Local climates are also influenced by altitude, proximity to oceans, mountain ranges, and prevailing winds.
Earth's climate has changed naturally throughout its history. Periods of extensive glaciation have alternated with warmer intervals. In the modern period, human activities have significantly increased atmospheric concentrations of greenhouse gases and contributed to ongoing climate change.
Water is one of Earth's defining characteristics. It exists naturally in solid, liquid, and gaseous forms. Most of Earth's water is contained in the oceans, while smaller amounts are stored in ice caps, glaciers, groundwater, lakes, rivers, soil, and the atmosphere.
The continuous movement of water through the environment is known as the water cycle. Water evaporates from surfaces, enters the atmosphere as water vapour, condenses into clouds, and returns to the surface through precipitation. Water can then flow over land, enter rivers and oceans, or infiltrate into the ground.
The presence of abundant liquid water has played an important role in the development and persistence of life on Earth.
Earth is the only known planet with an active global system of plate tectonics. Its rigid outer shell, the lithosphere, is divided into large plates that move slowly over the more ductile material beneath them.
Interactions between tectonic plates produce many geological features and events. Plates may move apart at divergent boundaries, collide at convergent boundaries, or slide past one another at transform boundaries.
Plate tectonics contributes to the formation of mountains, ocean basins, volcanoes, and earthquakes. It also plays an important role in the long-term carbon cycle and the recycling of material between Earth's surface and interior.
Earth has one known natural satellite, the Moon. The Moon is the fifth-largest natural satellite in the Solar System and is approximately 384,400 kilometres from Earth on average.
The gravitational interaction between Earth and the Moon produces tides in Earth's oceans and contributes to the stabilization of Earth's axial orientation. The Moon's phases result from the changing geometry of the Earth, Moon, and Sun as the Moon orbits Earth.
The Moon has also played an important role in human culture, calendars, navigation, and scientific research.
Earth rotates around its axis once approximately every 24 hours. This rotation produces the regular cycle of day and night. Earth's axis is tilted relative to the plane of its orbit around the Sun.
Earth completes one orbit around the Sun in approximately 365.25 days. The extra fraction of a day is accounted for by the leap year system used in many calendars.
Earth's axial tilt causes different parts of the planet to receive varying amounts of sunlight throughout the year. This produces the seasons.
Earth is the only known planet on which life exists. Life is found in environments ranging from deep oceans and underground rocks to deserts, polar regions, forests, and the atmosphere.
Living organisms on Earth include bacteria, archaea, fungi, plants, and animals. These organisms interact through complex ecosystems and food webs.
The history of life on Earth extends back at least several billion years. Early life was predominantly microscopic. Over time, organisms evolved increasing levels of biological complexity, eventually producing multicellular life and the diverse ecosystems present today.
The development of photosynthesis had a major effect on Earth's environment because it released oxygen into the atmosphere. The resulting increase in atmospheric oxygen helped enable the evolution of many forms of complex life.
Earth contains an enormous diversity of living organisms. Biodiversity varies between environments and is particularly high in some tropical ecosystems, including rainforests and coral reefs.
Species interact with one another and with their physical surroundings. These interactions include predation, competition, mutualism, decomposition, and nutrient cycling.
Human activities have altered many ecosystems and have contributed to habitat loss, pollution, overexploitation of natural resources, and declines in populations of some species. Conservation efforts seek to protect ecosystems and maintain biological diversity.
Modern humans, Homo sapiens, evolved in Africa and subsequently spread to nearly every major land region of Earth. Human societies have developed a wide variety of languages, cultures, religions, political systems, technologies, and economic systems.
The development of agriculture allowed many human populations to establish permanent settlements and contributed to the growth of cities and complex societies. Later developments in science, industry, transportation, and communications greatly increased humanity's ability to alter and interact with the planet.
Today, Earth is home to billions of people living in numerous countries and territories. Human activities influence the planet's atmosphere, oceans, landscapes, ecosystems, and climate.
People have studied Earth for thousands of years through observation, measurement, mapping, and exploration. Modern scientific disciplines such as geology, geography, meteorology, oceanography, ecology, and climatology examine different aspects of the planet.
The development of satellites and spacecraft has allowed scientists to observe Earth from space. Earth observation satellites are used to study weather, climate, vegetation, oceans, ice, land use, and natural disasters.
Space-based observations have also demonstrated that Earth is a dynamic system in which the atmosphere, oceans, land, ice, and living organisms interact continuously.
Earth will continue to change as geological and biological processes operate over long periods. Continents will move, mountains will form and erode, oceans will change, and ecosystems will evolve.
Over much longer timescales, the increasing luminosity of the Sun is expected to make Earth progressively less suitable for complex life. Eventually, billions of years from now, the Sun will enter the red giant stage of its evolution, dramatically altering the conditions in the inner Solar System.