The Four Spheres of the Earth and Earthquake Study

The Four Spheres of the Earth

The Earth can be divided into four systems or spheres: geosphere, atmosphere, hydrosphere, and biosphere. They all interact very closely with each other.

Geosphere

Scientists theorize that about 4.5 billion years ago, the Earth was a large ball of molten rock. The molten state was due to three processes that generated heat:

• The continuous impacts of planetesimals during accretion
• The differentiation of materials, due to gravity, into three layers of increasing density: crust, mantle, and core

Atmosphere

During the gravitational differentiation process, large quantities of gas were emitted. Hydrogen and helium escaped into space. Others, such as carbon dioxide and water vapor, were trapped in the crust. A primitive atmosphere was formed from intense volcanic activity.

Hydrosphere

Later, the water in the atmosphere condensed. Heavy rainfall flooded the depressions on the solid surface, forming the hydrosphere.

Biosphere

Life on the Earth was made possible by two factors: the distance between the Earth and the Sun, and the physical and chemical conditions on the Earth, such as temperature and the presence of liquid water. The oxygenation of the atmosphere, the formation of soil, and the creation of thick bands of rock such as limestone.

Geologists study earthquakes to understand the interior of the Earth. Earthquakes are violent shaking events caused by sudden movements of the crust. They occur when large masses of rock located at fault lines suddenly slip past one another, releasing energy. The hypocenter is the point within the Earth where an earthquake originates. From here, oscillations (vibrations) travel through the inner layers of the Earth as seismic waves: P-waves and S-waves. Surface waves spread from the epicenter, sometimes with catastrophic effects.

Primary waves (P-Waves)

These are the fastest waves. The particles oscillate in the same direction as the wave through compression and expansion. The waves can travel through solid and liquid materials. However, they travel through liquids more slowly.

Secondary waves (S-Waves)

These are slower, so they are detected by seismographs after the P-waves. The particles oscillate perpendicularly to the direction of the wave. They travel through solids, but not liquids.