🌎 Our Home Planet The big picture
Earth is the third planet from the Sun and the only place we know of that has life. It formed about 4.54 billion years ago, and it is a layered world: a rocky, metallic interior wrapped in oceans, ice, air and living things. Scientists describe the planet as a set of interacting spheres, the lithosphere (or geosphere), hydrosphere, cryosphere, atmosphere and biosphere, and below the surface as four interior layers: crust, mantle, outer core and inner core.
This site tours all of it, then points to Earth's companion, The Moon, which has its own site with everything we can gather on what it is made of. Looking for something specific? Visit Planet Continent, Planet Ocean, Planet Mountain, Volcano, Earthquake, Glacier and Climatology.
What the whole Earth is made of
Approximate share of the planet's mass by element. Most of the iron is in the core, so the crust we live on looks very different (see the Interior section).
🌐 Earth's Spheres The systems that make the planet work
Earth science splits the planet into connected systems. Each is a "sphere" of matter, and they constantly exchange energy, water, carbon and nutrients: a volcano (lithosphere) puts ash into the air (atmosphere), which cools the climate and changes rain (hydrosphere) and ice (cryosphere), which changes what can live where (biosphere). Choose a sphere below.
Where Earth's water is
Share of all water on Earth (about 1.386 billion km³), after USGS. Only about 2.5% is fresh water, and about two-thirds of that is locked in ice.
- Salinity: seawater averages about 35 g of salt per kg, mostly sodium chloride.
- Pacific Ocean: holds about half of all the ocean water.
- Water cycle: roughly 500,000 km³ evaporates and falls as rain or snow each year.
Where the fresh water is
Share of fresh water, approximate. Lakes, rivers, soil and the air together hold only a tiny fraction, yet they supply most of what people and ecosystems use.
- Antarctica holds roughly 90% of all ice, and Greenland most of the rest.
- Groundwater in aquifers such as the Ogallala (USA) and the Nubian Sandstone (Africa) is being drawn down faster than it refills in some regions.
- Rivers hold only about 0.0002% of Earth's water but move the most water to the sea.
How the spheres interact
🧭 Inside the Earth Crust, mantle, outer core and inner core
Nobody has been deeper than the crust. The deepest hole ever drilled, Russia's Kola Superdeep Borehole, reached about 12.3 km, which is less than 0.2% of the way to the centre (6,371 km). What we know of the interior comes from earthquake waves, which speed up, slow down, bend and bounce at boundaries, plus gravity, magnetism, lab experiments and meteorites. Select a layer on the diagram.
Cross-section drawn to scale by radius. The crust is thinner than the line would be at true scale, so it is slightly exaggerated.
The layers compared
Depths, temperatures and densities are approximate and vary by source and location. Pressure at the centre is about 3.6 million times atmospheric pressure (roughly 360 GPa).
Share of Earth's mass
Share of Earth's volume
Approximate. The thin crust is under 1% of the mass, while the dense core is about a third.
The crust's ingredients
Elements in the continental crust by mass, approximate. Oxygen and silicon alone make up about three-quarters, mostly as silicate minerals like feldspar and quartz.
How we know: seismic waves & boundaries
🛰️ The Atmosphere's Five Layers From the ground to the edge of space
The air is a thin shell: half its mass is below about 5.5 km and 99% below about 30 km. It is divided into five layers by how temperature changes with height. For clouds, storms and climate see Planet Climatology.
Layers (not to scale)
A schematic: the lower layers are drawn larger than their true height so they can be read. The troposphere is only about 8 to 15 km thick; the exosphere fades into space over thousands of kilometres.
- Mount Everest: 8.8 km, in the upper troposphere.
- Airliners: about 10 to 12 km, at the top of the troposphere.
- Kármán line: 100 km, the usual edge of space.
- International Space Station: about 400 km, in the thermosphere.
What the air is made of
Dry air by volume. Carbon dioxide is only about 0.04% of the air, yet it has an outsized effect on climate. Water vapour varies from near 0 to about 4%.
- Nitrogen is chemically calm and dilutes the oxygen; some is turned into plant food by bacteria and lightning.
- Oxygen comes almost entirely from photosynthesis.
- Argon is inert, made by the radioactive decay of potassium in rock.
- Carbon dioxide and methane are the main long-lived greenhouse gases that people are increasing.
Why the atmosphere matters
🧩 Plate Tectonics Why the surface moves
The lithosphere is broken into about 15 large and small rigid plates that ride on the softer, slowly flowing asthenosphere of the upper mantle. They move a few centimetres a year, about as fast as fingernails grow. Where they meet, mountains rise, trenches open, and earthquakes and volcanoes occur. See also Planet Continent for Pangea and how the continents moved.
The seven major plates
🧲 Magnetic Field, Rotation & Orbit Earth in motion
Earth is never still: it spins, circles the Sun, wobbles, and generates a magnetic field that shields the surface from charged particles from space.
⏳ Earth's History 4.54 billion years in brief
The "Ga" below means billions of years ago and "Ma" millions of years ago. Dates are approximate and some are still debated.
Five mass extinctions
Percentages are rough estimates of marine species lost. Many scientists think a sixth extinction, driven by people, may be underway.
📡 Explore the Earth Extremes, plate boundaries, water and ice, with live NASA layers
Pins mark Earth's extremes and the places where the processes on this page can be seen. Use the layer button (top right of the map) to add NASA satellite layers: true-colour clouds, sea-surface temperature and surface air temperature, each from about two days ago. Tap a pin for a summary.
Satellite layers: NASA GIBS. Imagery: Esri, Maxar, Earthstar Geographics.
🌙 Next door: The Moon
What the Moon is made of, its interior, surface, ice, origin, orbit and tides, moonquakes, and every crewed mission with its ship names and astronauts, plus a map of landing sites.
Explore The Moon ›