Earth: A Geologically Active Planet
Orbital and Physical Parameters
Earth is the third planet from the Sun and the largest and densest of the terrestrial planets. It orbits the Sun on an elliptical path with a mean distance of 149.6 million km (1 Astronomical Unit). The sidereal orbital period is 365.25 days. The rotation period on its axis defines the day, lasting 24 hours. The tilt of the Earth’s axis by approx. 23.44 degrees relative to the ecliptic is the primary cause of seasonal variations.
Key Facts about Earth
| Feature | Value |
|---|---|
| Diameter | 12,742 km |
| Mass | 5.972 x 10^24 kg |
| Mean Distance from the Sun | approx. 149.6 million km (1 AU) |
| Orbital Period around the Sun | 365.25 days |
| Rotation Period | 24 hours |
| Surface Temperature | -88 °C to +58 °C |
| Atmosphere | 78% Nitrogen, 21% Oxygen, 1% other gases |
| Number of Moons | 1 (the Moon) |
| Albedo (Reflectivity) | 0.30 |
| Surface Coverage | 71% Water, 29% Land |
Structure and Dynamics
The Earth’s internal structure consists of a solid, metallic inner core and a liquid outer core, the latter generating a global magnetic field (Geomagnetic Field). This field shields the atmosphere from the solar wind. Above this lies the mantle, followed by the thin, lithospheric crust.
The crust is fractured into several tectonic plates. The motion of these plates (plate tectonics) results in phenomena such as earthquakes, volcanism, and mountain building. Earth is the only known terrestrial planet on which this process is actively occurring.
Hydrosphere and Atmosphere
Approximately 71% of the Earth’s surface is covered by liquid water, primarily in the form of oceans. This is a critical feature distinguishing Earth from all other planets.
The atmosphere is a complex, layered system responsible for the climate and habitability. Its main constituents are:
- Nitrogen (N2): approx. 78%
- Oxygen (O2): approx. 21%
- Argon, Water Vapor, CO2: approx. 1%
The release of O2 into the atmosphere was facilitated by the photosynthesis of living organisms. The ozone layer in the stratosphere (approx. 10 to 50 km altitude) absorbs the majority of the Sun’s harmful ultraviolet radiation.
Biosphere and Moon
Earth is the only location in the universe where active life has been confirmed. The biosphere interacts profoundly with the atmosphere, hydrosphere, and lithosphere (geochemical cycles).
Earth’s natural satellite, the Moon, is exceptionally large relative to its parent planet. The Moon stabilizes the tilt of the Earth’s axis over long geological timescales, contributing to a more stable climatic history. Its gravitational pull is also the primary cause of the tides in the oceans.