Understanding the Formation of Earth and Its Layers
Theory of Planetesimals
Initial Nebula
The rotating nebula of dust and gas began to contract.
Gravitational Collapse
The contraction or collapse formed a central mass of gravity and a disk around it.
Formation of Protosun
The collision of particles in the central mass released a large amount of energy.
Planetesimal Formation
The process followed gravitational attraction, causing particles around the sun to collide and group together to form larger planetesimals.
Formation of the Earth
Accretion of Planetesimals
As collisions caused larger planetesimals to form, their greater gravitational field favored the accretion of new planetesimals. The temperature increased due to the impacts of planetesimals.
The Earth’s temperature was such that the materials were partially melted, favoring the distribution of density components according to their properties.
The escaped gases formed the early atmosphere.
The possible cooling of surface water vapor condensed, leading to the formation of oceans.
Methods of Study
Direct Methods
These methods allow observation of areas with access to materials from the interior found on the surface.
Indirect Methods
We infer the interior characteristics from various types of data.
Mines
Excavations are made for minerals.
Surveys
Holes are drilled in the subsoil.
Geothermal Gradient
Inside the Earth, temperature increases.
Volcanoes
Eruptions bring material from inside the Earth. Most of the materials are partially melted, and the magma drags rock fragments that are not fully melted.
Seismic Methods
Based on the study of earthquakes and how the waves travel.
Seismic Waves
P-waves: They move faster and are longitudinal waves, compressing and dilating rocks alternately.
S-waves: They travel more slowly and are transverse, vibrating perpendicular to the direction of wave propagation.
The rate at which seismic waves propagate depends on the characteristics of the materials through which they travel. Each variation produces a change in the direction of wave advance.
Earth’s Structure
Core
The central area of the Earth, located beneath the Gutenberg discontinuity, consists mostly of iron and nickel.
The outer core is liquid and is stirred by convection currents, playing a key role in the creation of a gravitational mantle.
The inner core is solid and is located in the crystallized iron at the bottom.
Mantle
The inner layer located between the discontinuity and the Mohorovicic boundary represents 83% of the total volume of the Earth. Its most abundant elements are O, Si, Mg, and Fe.
Upper Mantle
It lies beneath the lithosphere and is in a solid state.
Lower Mantle
Found under convection flows, driven by temperature differences.
Crust
The thin outer layer of the Earth extends from the surface to the Mohorovicic discontinuity. Its components include O, Si, Al, Fe, and Ca.
Lithosphere
The rigid external part includes the entire crust and part of the upper mantle.
Continental Lithosphere
It is between 25 and 70 km thick, very heterogeneous, and composed of denser rocks. The lower half is dominated by metamorphic rocks, with abundant sedimentary rocks.
Oceanic Lithosphere
It is very thin, with a thickness between 5 and 10 km, and consists of stratified levels: sediments, basalts, and younger rocks.