Quick Facts
What Is Earth?
Earth is a terrestrial (rocky) planet with a solid surface, a global ocean covering most of its area, and an atmosphere rich in nitrogen and oxygen. It orbits the Sun at an average distance of about 93 million miles (one astronomical unit) in the region often called the habitable zone.
The planet is constantly changing through plate tectonics, the water cycle, atmospheric circulation, and the activity of living organisms. These interacting systems create the conditions that make Earth unique in the solar system.
Internal Structure
Crust
The thin outer shell of solid rock. Continental crust is thicker and less dense than oceanic crust.
Mantle
A thick layer of hot, solid rock that flows slowly over long timescales, driving plate tectonics.
Outer Core
A liquid layer of iron and nickel whose motion generates Earth’s magnetic field.
Inner Core
A solid sphere of iron and nickel at extreme temperature and pressure in the center of the planet.
Earth’s Major Systems
Atmosphere
The layer of gases surrounding the planet. It moderates temperature, protects from radiation, and enables weather and climate.
Hydrosphere
All of Earth’s water—oceans, rivers, lakes, groundwater, ice, and water vapor. Oceans cover about 71% of the surface.
Geosphere
The solid Earth: rocks, minerals, landforms, and the processes of plate tectonics, volcanism, and erosion.
Biosphere
The realm of life, from the deepest ocean trenches to the upper atmosphere, interacting with all other systems.
Why Earth Supports Life
Distance from the Sun
Located in the habitable zone where temperatures allow liquid water to exist on the surface.
Magnetic Field
Generated by the outer core, it shields the surface from much of the solar wind and harmful radiation.
Atmosphere & Water
A protective atmosphere and abundant liquid water create stable conditions for complex chemistry and life.
Earth in the Solar System
Earth is one of four terrestrial planets (along with Mercury, Venus, and Mars). It has one natural satellite—the Moon—which stabilizes Earth’s axial tilt and influences tides. The planet completes one orbit around the Sun in about 365.25 days and rotates once on its axis in about 24 hours, creating the cycles of day, night, and seasons.
Compared with its neighbors, Earth is distinguished by active plate tectonics, a strong magnetic field, surface liquid water, and a biosphere.
A Living Planet
Earth is a complex, interconnected system of rock, water, air, and life. Its internal heat, magnetic field, atmosphere, and position in the solar system combine to create the only known environment that sustains a rich biosphere.
Understanding Earth’s structure, systems, and history provides the foundation for studying climate, natural resources, hazards, and the conditions that make our planet habitable.