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 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

    PropertyValue
    Equatorial Diameter~12,742 km
    Mass5.972 × 10²⁴ kg
    Distance from the Sun~149.6 million km (1 AU)
    Orbital Period365.25 days
    Rotation Period23 h 56 min 4 s
    Moons1 (the Moon)
    AtmosphereNitrogen (78%), Oxygen (21%), trace gases

    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.

Early Concepts

Humans have pondered the nature of Earth since ancient times. Many early civilizations envisioned a flat Earth or mythical landmasses resting on animals or pillars. However, ancient Greek thinkers proposed a spherical Earth, supported by observations like the Earth’s shadow on the Moon during lunar eclipses. Around 240 BCE, Eratosthenes calculated Earth’s circumference with remarkable accuracy using shadow lengths in Egypt.

The Copernican Revolution

In the 16th century, Nicolaus Copernicus challenged the geocentric worldview with his heliocentric model. Earth was now understood as just one of several planets orbiting the Sun. This revolution transformed astronomy and laid the groundwork for modern science.

The Space Age

The advent of spaceflight in the 20th century allowed humans to observe Earth from beyond its atmosphere. In 1957, the Soviet Sputnik 1 became the first artificial satellite in Earth orbit. The famous “Blue Marble” photograph, taken by the Apollo 17 mission in 1972, became an icon of planetary unity and environmental awareness.

Since then, Earth observation satellites have provided essential data for climate science, agriculture, disaster response, and geoscience. Space stations like the ISS continuously observe Earth and support research in microgravity.

Earth Science Research

Modern Earth science encompasses disciplines such as geology, meteorology, oceanography, and geophysics. Tools like GPS, remote sensing, deep-sea drilling, and seismic measurements allow scientists to study Earth's internal structure, tectonic activity, environmental change, and planetary systems in detail.

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