Introduction
Earth is the third planet from the Sun and the largest of the Solar System's four terrestrial planets. It is a rocky planet with a dynamic interior, a substantial atmosphere, extensive oceans and a biosphere containing an extraordinary diversity of life. Follow this link to find out more about our world: world-wide-web.uk.
Earth formed approximately 4.5 billion years ago as material in the young Solar System accumulated under gravity. Today it is the only world known to support life. NASA notes that Earth's liquid water, suitable temperature range and chemical environment make it exceptionally hospitable to life as we know it.
Key Facts About Earth
| Property | Approximate Value |
|---|---|
| Position from the Sun | Third planet |
| Age | About 4.5 billion years |
| Equatorial diameter | About 12,756 km |
| Mean distance from Sun | About 150 million km |
| Natural satellites | One — the Moon |
| Surface covered by ocean | About 71% |
| Atmospheric nitrogen | About 78% |
| Atmospheric oxygen | About 21% |
| Rings | None |
NASA gives Earth's equatorial diameter as approximately 12,756 km and its mean distance from the Sun as approximately 150 million km, exactly one astronomical unit by definition.
```Formation of Earth
Earth formed during the early history of the Solar System from material orbiting the young Sun.
Small rocky bodies collided and accumulated through a process known as accretion. As the growing planet became more massive, gravity increasingly shaped its structure.
Earth's interior eventually differentiated into layers. Dense metallic material migrated toward the centre while silicate material formed the mantle and crust.
Earth has a lot of things going on on its planet. To find out more, see our world .
Internal Structure of Earth
Earth has a layered internal structure consisting principally of the crust, mantle, outer core and inner core.
| Layer | Description |
|---|---|
| Crust | Thin outer rocky layer. Continental crust is generally thicker than oceanic crust. |
| Mantle | Thick silicate layer extending beneath the crust. It behaves as a solid over short timescales but can flow slowly over geological time. |
| Outer Core | Liquid layer dominated by iron and nickel. |
| Inner Core | Solid, extremely hot, dense metallic region at the centre of Earth. |
The Crust
The crust is Earth's outermost solid layer.
There are two principal types:
Continental Crust
Generally thicker and less dense than oceanic crust. It forms the foundations of continents.
Oceanic Crust
Generally thinner and denser. It forms much of the seafloor and is continuously created and recycled by plate tectonic processes.
The Mantle
The mantle is the thickest major layer of Earth.
It consists predominantly of silicate minerals rich in elements such as magnesium and iron.
Although the mantle is predominantly solid, it can deform and flow slowly over geological timescales. This slow movement contributes to the large-scale dynamics of Earth's lithosphere.
```The Core
Earth's core is dominated by iron and nickel.
The outer core is liquid, while the inner core is solid because the enormous pressure at Earth's centre raises the melting temperature of the material.
Earth's Atmosphere
Earth's atmosphere is a mixture of gases surrounding the planet. Near the surface, it consists primarily of nitrogen and oxygen, together with smaller quantities of argon, carbon dioxide, water vapour and other gases.
| Gas | Approximate Proportion |
|---|---|
| Nitrogen | 78% |
| Oxygen | 21% |
| Argon and other gases | About 1% |
The atmosphere is essential to life, regulates temperature, transports water and provides protection from many forms of incoming radiation and small meteoroids.
```Layers of the Atmosphere
| Layer | Main Characteristics |
|---|---|
| Troposphere | Lowest layer; contains most atmospheric mass and essentially all ordinary weather. |
| Stratosphere | Contains the ozone layer and becomes warmer with increasing altitude in its upper regions. |
| Mesosphere | Region where many incoming meteoroids burn up. |
| Thermosphere | Very thin atmosphere with temperatures strongly influenced by solar radiation. |
| Exosphere | Extremely diffuse outer region gradually merging into space. |
NASA identifies five principal atmospheric layers based on temperature, composition and density.
```Earth's Oceans
Approximately 71% of Earth's surface is covered by ocean. The global ocean contains about 97% of Earth's water.
Earth's oceans are essential components of the planetary climate system. They store enormous quantities of heat, transport energy through ocean currents and participate in the global carbon and water cycles.
Pacific Ocean
The largest and deepest of Earth's oceans.
Atlantic Ocean
Separates the Americas from Europe and Africa and contains major climate-regulating circulation systems.
Indian Ocean
Extends between Africa, Asia and Australia.
Southern Ocean
Surrounds Antarctica and plays an important role in global ocean circulation.
Arctic Ocean
The smallest and shallowest of the major oceans, centred on the Arctic region.
The Water Cycle
Earth's water continuously moves between the atmosphere, oceans, land and living organisms.
Solar energy drives much of this cycle by providing the energy required for evaporation.
```Plate Tectonics
Earth's lithosphere is divided into large tectonic plates that move slowly over geological time.
Plate boundaries are associated with many major geological processes, including earthquakes, volcanism, mountain building and the creation and destruction of oceanic crust.
| Boundary | Process |
|---|---|
| Divergent | Plates move apart and new crust can form. |
| Convergent | Plates move together; subduction or mountain building may occur. |
| Transform | Plates slide laterally past one another. |
Volcanoes and Earthquakes
Earth is geologically active. The movement of tectonic plates continually reshapes its surface.
Volcanoes
Volcanoes provide pathways through which molten or partially molten material and volcanic gases can reach the surface.
Earthquakes
Earthquakes occur when accumulated stress in the Earth's crust and lithosphere is released, often along faults associated with tectonic plate motion.
```Earth's Magnetic Field
Earth possesses a global magnetic field generated primarily by processes within its electrically conducting liquid outer core.
The magnetic field creates a protective environment around the planet and interacts with charged particles arriving from the Sun.
The Magnetosphere
The magnetosphere is the region of space dominated by Earth's magnetic field.
The solar wind compresses the sunward side of the magnetosphere and stretches the field into a long magnetotail on the night side.
Interactions between solar particles and Earth's magnetic field can produce spectacular auroras.
```Earth's Climate System
Earth's climate results from interactions among the atmosphere, oceans, land, ice and biosphere, driven ultimately by energy from the Sun and modified by Earth's internal processes.
Atmosphere
Transports heat and water and regulates the planet's energy balance.
Oceans
Store and redistribute enormous quantities of heat.
Ice
Reflects incoming sunlight and influences sea level and climate feedbacks.
Biosphere
Living organisms influence atmospheric chemistry and global carbon and nutrient cycles.
The Greenhouse Effect
Certain atmospheric gases absorb and re-emit infrared radiation, producing the natural greenhouse effect that keeps Earth's surface substantially warmer than it would otherwise be.
Human activities have increased concentrations of several greenhouse gases, altering Earth's radiative balance and contributing to modern climate change.
```Life on Earth
Earth is currently the only planet known to support life. NASA states that, so far, all confirmed life known to science exists on Earth.
Life has adapted to an extraordinary range of environments, including oceans, deserts, polar regions, deep underground environments and high-altitude ecosystems.
Biosphere
The global collection of ecosystems and living organisms.
Oceans
Contain enormous microbial and multicellular ecosystems.
Forests
Major terrestrial ecosystems involved in carbon and water cycles.
Microbial Life
Microorganisms occupy environments ranging from ocean sediments to extreme terrestrial habitats.
Earth and the Origin of Life
Evidence indicates that life was established on Earth billions of years ago. NASA notes that Earth's oceans provided an important environment for the emergence of life around 3.8 billion years ago.
The precise pathway by which non-living chemistry developed into the first biological systems remains an active scientific problem.
Research into this question connects planetary science, chemistry, geology, biology and astrobiology.
```Earth's Rotation
Earth rotates around its axis, producing the cycle of day and night.
Earth's rotation is also important to atmospheric and oceanic circulation through the Coriolis effect.
```Earth's Orbit
Earth travels around the Sun in an approximately elliptical orbit.
Earth's average distance from the Sun is one astronomical unit, approximately 150 million km.
```The Seasons
Earth's seasons are primarily caused by the tilt of Earth's rotational axis relative to the plane of its orbit around the Sun.
Spring
A transitional season between winter and summer.
Summer
The hemisphere tilted toward the Sun receives more direct sunlight and longer daylight.
Autumn
A transition between summer and winter.
Winter
The hemisphere tilted away from the Sun receives less direct sunlight and shorter daylight.
Earth as a Planetary System
Earth is best understood not as an isolated rock but as a continuously interacting planetary system.
| Component | Major Role |
|---|---|
| Geosphere | Solid Earth, including rocks, minerals and the interior. |
| Hydrosphere | Earth's oceans, rivers, lakes, groundwater and other water reservoirs. |
| Atmosphere | Gaseous envelope surrounding the planet. |
| Cryosphere | Frozen water including glaciers, ice sheets and sea ice. |
| Biosphere | All known living organisms and their ecosystems. |
Exploring Earth from Space
Earth is extensively studied using satellites and spacecraft. Space-based observations allow scientists to observe the planet as an integrated system.
Weather Satellites
Monitor clouds, storms, atmospheric temperature and precipitation.
Earth Observation
Measures land cover, vegetation, ice, oceans and environmental change.
Climate Satellites
Monitor long-term changes in Earth's atmosphere, oceans, ice and land systems.
Gravity Missions
Map variations in Earth's gravitational field to investigate changes in mass distribution.
NASA notes that numerous spacecraft study Earth from orbit as a whole system, observing the atmosphere, oceans, glaciers and solid Earth.
```Earth Observation and Scientific Research
Modern Earth science combines measurements from satellites, aircraft, ships, ground stations, geological surveys and computer models.
These observations are used to investigate:
- Climate change
- Weather and extreme events
- Ocean circulation
- Sea-level change
- Glacier and ice-sheet dynamics
- Deforestation and land-use change
- Atmospheric chemistry
- Earthquakes and volcanic activity
- Water resources
- Ecosystem change
Earth Compared with Other Terrestrial Planets
| Property | Mercury | Venus | Earth | Mars |
|---|---|---|---|---|
| Rocky | Yes | Yes | Yes | Yes |
| Global surface oceans | No | No | Yes | No today |
| Substantial atmosphere | Very thin | Very dense | Yes | Thin |
| Known life | No | No | Yes | No confirmed life |
| Natural satellites | 0 | 0 | 1 | 2 |
Earth and the Milky Way
Earth is part of the Solar System, which lies within the Milky Way galaxy.
The Solar System is located in a smaller structure of the Milky Way known as the Orion Arm, or Orion Spur, between the larger Sagittarius and Perseus arms.
The Solar System takes approximately 230 million years to complete one orbit around the centre of the Milky Way.
```The Future of Earth
Earth's future will be determined by both astronomical and geological processes.
Near-Term Geological Future
Plate tectonics, erosion, volcanism, climate processes and biological evolution will continue to reshape the planet over geological timescales.
Solar Evolution
On a much longer timescale, the evolution of the Sun will have a profound effect on Earth.
The Sun will gradually become more luminous as it evolves. Several billion years from now it will leave the main sequence and expand into a red giant.
Major Scientific Questions About Earth
- How exactly did life originate?
- How did Earth's first atmosphere and oceans develop?
- How does the deep Earth generate and sustain its magnetic field?
- How will Earth's climate system change in the future?
- How do tectonic plates interact with the deep mantle?
- How do Earth's oceans and atmosphere exchange energy and gases?
- How resilient are Earth's ecosystems to environmental change?
- How did Earth's Moon form?
- How representative is Earth among potentially habitable planets?
Historical Timeline
Earth as a Habitable Planet
Earth's habitability results from the interaction of many characteristics rather than from a single factor.
Liquid Water
Earth's surface environment permits persistent liquid water over vast regions.
Atmosphere
The atmosphere provides pressure, chemical resources and climate regulation.
Magnetic Field
Earth's magnetosphere interacts with the solar wind and forms part of the planet's space environment.
Geological Activity
Plate tectonics and the carbon cycle contribute to the long-term evolution of Earth's environment.
Stable Star
The Sun provides a long-lived source of energy for the Earth's climate and biosphere.
Conclusion
Earth is a dynamic rocky planet whose atmosphere, oceans, continents, interior, magnetic field and biosphere interact as parts of a complex planetary system.
It formed approximately 4.5 billion years ago and has undergone enormous geological and biological changes since its formation. Its oceans cover about 71% of the surface, while its atmosphere provides the gases and pressure necessary for the ecosystems that support life.
Earth and the Milky Way
Earth is part of the Solar System, which lies within the Milky Way galaxy.
The Solar System is located in a smaller structure of the Milky Way known as the Orion Arm, or Orion Spur, between the larger Sagittarius and Perseus arms.
Earth is also part of a much larger hierarchy: it is a planet in the Solar System, the Solar System is part of the Milky Way , and the Milky Way Milky Way is one galaxy among an enormous population of galaxies in the Universe.