Earth’s Formation and Internal Structure: A Deep Dive
The Formation of Earth
The history of Earth dates back to the origins of the solar system, when it was barely beginning to differentiate as a planet. Reconstructing this complex stage is challenging due to the limited traces of the events that occurred.
[So came the Earth and its internal structure]
1The solar nebula, like all nebulae, must have been constituted of cosmic gases and dust. Initially, this process was slow.
2Under the influence of gravity, the nebula contracted, spinning more quickly and warming up due to collisions among the particles.
3The solar nebula flattened, taking the shape of a disc where most of the material was condensed in the center. The remaining materials stayed in the disc and gradually grouped into larger bodies called planetesimals, which collided with each other, forming even larger bodies over time.
4Approximately 4.6 billion years ago, the primitive planets originated, orbiting around the sun. This mechanism of planet formation is called accretion. Numerous collisions of planetesimals impacted the primitive Earth, elevating its temperature and favoring the differentiation of its materials.
Studying Earth’s Interior
The deepest areas of the planet are inaccessible. Therefore, scientists use sophisticated research methods to interpret its internal structure. Understanding the structure of the geosphere is fundamental to comprehending terrestrial dynamics. The investigation of Earth relies on two types of methods:
- Direct Methods: These are based on the study of terrestrial materials. They have many limitations, as they have limited access to the mantle.
- Indirect Methods: These rely on various investigations, such as the analysis of igneous rocks, meteorites, studying the physical properties of Earth, or analyzing the propagation of waves produced by earthquakes, known as seismic methods.
Types of Waves
Longitudinal waves: Produced when a spring is stretched or compressed.
Transverse waves: Formed when a spring is moved laterally and vibrates perpendicular to the direction of wave propagation.
Seismic Waves: When an earthquake occurs, it produces different types of seismic waves:
- Surface waves: Responsible for the destructive effects of seismic movements.
- Primary waves (P) and secondary waves (S): Spread inside the Earth. They experience speed changes as they travel through different areas of the Earth, called seismic discontinuities. These changes occur because our planet is constituted of layers with different chemical compositions and behaviors under high pressures.
Primary Waves (P)
Spread through both liquid and solid media, although their speed decreases in liquid media. They are longitudinal waves, with compressions and expansions occurring parallel to the direction in which the seismic waves propagate.
Secondary Waves (S)
Slower than P waves and only propagate through solid media. They are transverse waves, where rocks vibrate inside the Earth in a direction perpendicular to the direction of seismic wave propagation.
Seismic Discontinuities
- Moho: The boundary between the crust and the mantle. The speed of P and S waves increases.
- Discontinuity of the 670km: Located 670km deep. Separates the upper and lower mantle. The speed of P and S waves increases.
- Gutenberg Discontinuity: Separates the core and the mantle, situated at 2900km. S waves stop spreading, and P waves reduce their speed.
- Lehmann Discontinuity: Separates the outer and inner core. The speed of P waves increases.
Geochemical Modeling
According to the geochemical model, the geosphere is divided into 3 layers with different chemical compositions:
Cortex: Situated at the Mohorovicic seismic discontinuity and is solid.
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