Earth is the third planet from the Sun in the Solar System, a rocky, differentiated world that formed about 4.54 billion years ago and today supports a global biosphere. Key bulk properties include a mass of 5.9722×10^24 kg, a mean radius of 6,371 km, and a Bond albedo near 0.294, according to NASA’s planetary fact sheets (NASA NSSDC). Radiometric dating of meteorites and the oldest terrestrial and lunar materials constrains Earth’s age to approximately 4.54 ± 0.05 billion years (Britannica).

Position, orbit, and rotation

Earth orbits the Sun at a mean distance of ~149.6 million km (1 AU) with a sidereal orbital period of ~365.256 days; its obliquity is ~23.44°, which, combined with its nearly 24-hour rotation, produces the seasons. These parameters are compiled by NASA’s planetary fact sheets (NASA NSSDC). Earth has one large natural satellite, the Moon, whose average distance is ~384,400 km and whose gravitational interaction drives the dominant tidal cycles (NASA NSSDC).

Internal structure and Plate Tectonics

Seismic, geodetic, and geochemical evidence shows a layered interior: a thin crust (oceanic crust typically ~5–10 km; continental crust averaging ~30–40 km, thicker under major ranges), a silicate mantle to ~2,900 km depth, and a metallic core with a liquid outer shell and a solid inner core. This structure underpins plate tectonics, whereby rigid lithospheric plates diverge at mid-ocean ridges, converge at subduction zones, and translate along transform faults, recycling crust and driving orogeny and volcanism (USGS “This Dynamic Earth”; Britannica). Mantle convection supplies the mechanical energy for plate motions and regulates long-term heat loss (Britannica).

Hydrosphere and cryosphere

Approximately 71% of Earth’s surface is covered by water, with oceans holding about 96.5% of all water on the planet. Fresh water is concentrated in ice sheets, glaciers, and groundwater, with lakes and rivers comprising only a tiny fraction of the total. These widely cited proportions are summarized by the U.S. Geological Survey (USGS). The deepest surveyed point in the global ocean is Challenger Deep in the Mariana Trench, measured at roughly 10,935 m below sea level; NOAA overviews and expeditions document both the maximum depth and ongoing mapping limitations (NOAA Ocean Exploration). The mid-ocean ridge system, at ~65,000 km length, is the planet’s longest mountain chain, formed by seafloor spreading (NOAA Ocean Exploration).

Surface extremes

The highest point on Earth’s surface, Mount Everest, was jointly remeasured by Nepal and China and announced in 2020 as 8,848.86 m above sea level (The Guardian). The greatest confirmed ocean depth, Challenger Deep, lies near 11,000 m beneath sea level (NOAA Ocean Exploration).

Atmosphere and the Carbon Cycle

The dry atmosphere by volume is about 78.08% nitrogen, 20.95% oxygen, and 0.93% argon, with trace gases—including carbon dioxide, methane, nitrous oxide, and ozone—comprising roughly 0.04%; water vapor varies regionally and seasonally. NASA summarizes these canonical dry-air fractions and their climatic roles (NASA Earth Science). Atmospheric CO₂ continues to rise: NOAA reports an annual global average near 422.8 ppm for 2024 and a Mauna Loa monthly average exceeding 430 ppm in May 2025, underscoring long-term growth in greenhouse forcing (NOAA Climate.gov; NOAA GML; Scripps CO₂ Program).

Magnetosphere

A self-sustaining geodynamo in the liquid outer core generates Earth’s global magnetic field, which shields the atmosphere and surface from charged solar and cosmic particles. NASA describes the convective, rotationally influenced fluid motions that produce the field and shape the magnetosphere (NASA Earth Science). Paleomagnetic records show numerous geomagnetic reversals; the most recent sustained reversal—the Brunhes–Matuyama—occurred about 780,000 years ago (ESA).

Origin and evolution of the biosphere

Biological activity is evident in the rock record by at least 3.5 billion years ago, with widely studied stromatolitic structures and microfabrics in Archean successions of Western Australia; while some older claims are debated, the consensus holds that early microbial ecosystems were established by the mid‑Archean (Live Science; Smithsonian Magazine). Oxygenic Photosynthesis by cyanobacteria fundamentally altered surface environments. The Great Oxidation Event (Paleoproterozoic, broadly ~2.4–2.1 Ga), recorded by red beds, loss of detrital pyrite/uraninite, and banded iron deposition patterns, marks the first sustained increase of atmospheric O₂, with later Neoproterozoic and Paleozoic steps toward near-modern levels (Britannica; Britannica—Proterozoic Eon).

Geological time and stratigraphic standards

Earth history is organized by the International Chronostratigraphic Chart maintained by the International Commission on Stratigraphy (ICS), which defines global units via ratified GSSPs (“golden spikes”) and provides continuously updated boundaries and nomenclature (ICS/IUGS). In March 2024, a proposal to formalize an Anthropocene epoch was rejected by the relevant subcommission and not advanced by ICS/IUGS; the formal timescale therefore continues to recognize the Holocene as the current epoch (Washington Post; ICS news).

Climate system

Multiple observing systems (surface stations, satellites, ocean reanalyses) show that anthropogenic greenhouse gas increases are warming the climate. The World Meteorological Organization confirmed 2024 as the warmest year in the instrumental record, with a global mean ~1.55 °C above the 1850–1900 baseline; decadal averages remain the primary benchmark for Paris Agreement goals (WMO—State of the Global Climate 2024). Rising CO₂, ocean heat content, and sea level, together with cryospheric changes, indicate persistent trends in the climate system (WMO).

Humanity and demography

Homo sapiens is a late Cenozoic species whose activities now shape biogeochemical cycles and ecosystems. The United Nations estimates the world population at roughly 8.2 billion by mid‑2024 and projects growth to peak near 10.3 billion in the mid‑2080s before modest decline by 2100 (UN DESA WPP 2024; UN Geneva summary). The U.S. Census Bureau estimated a world population of ~8.09 billion on January 1, 2025 (U.S. Census Bureau).

Notable numeric properties

Representative global means and reference values include: surface area ~510 million km² with ~361 million km² ocean and ~149 million km² land; mean surface temperature ~288 K (effective blackbody ~254 K); and escape velocity ~11.186 km/s (NASA NSSDC).

Galactic and planetary context

Earth orbits within the Milky Way and belongs to the inner cohort of rocky planets whose early accretion from the solar nebula is recorded by meteorites and planetary differentiation patterns. NASA’s comparative fact sheets summarize how Earth’s mass, density, and surface conditions differ from those of neighboring terrestrial planets (NASA NSSDC).