1 Earth
Earth is the third planet from the Sun and the only known celestial body to support life. It formed approximately 4.54 billion years ago and is characterized by a dense atmosphere and abundant liquid water — both critical factors for the development of life.
1.1 General Properties
1.2 Internal Structure
Earth is composed of several layers:
- Crust – the solid outer shell where continents and oceans reside.
- Mantle – the layer beneath the crust with high temperature and viscous rock flow.
- Core – Earth's innermost part, consisting of a liquid outer core and a solid inner core, made mostly of iron and nickel.
1.3 Atmosphere and Climate
Earth’s atmosphere protects it from harmful radiation and moderates the planet’s temperature via the greenhouse effect. Weather and climate are influenced by solar radiation, Earth’s rotation, ocean currents, and atmospheric circulation.
1.4 Hydrosphere
Approximately 71% of Earth’s surface is covered by water. Oceans are crucial for the climate system and host a vast range of life. Water is also found in the form of ice (in polar regions and glaciers) and as water vapor in the atmosphere.
1.5 Magnetic Field
Earth has a strong magnetic field generated by fluid motion in the outer core. This field protects the planet from solar wind and cosmic radiation and is responsible for phenomena such as the aurora borealis.
1.6 The Moon
Earth's only natural satellite is the Moon. Its gravitational influence causes tides and helps stabilize Earth’s axial tilt. Its surface is covered in craters, and its origin is most commonly explained by the giant-impact hypothesis.
1.7 Observation from Space
From orbit, Earth appears as a blue planet with swirling white clouds. The first full view of Earth was captured by Apollo 8 in 1968. Since then, satellites have continuously monitored Earth's systems from space.
1.8 Importance in Spaceflight
Earth is the point of origin for all human space activity and serves as a reference for the study of other planets. It provides the technological and scientific base for exploring space and searching for habitable exoplanets.