Understanding Lunar and Earth Structures: Key Concepts
Lunar Orbit: The Moon is the Earth’s natural satellite. The Moon orbits the Earth in its own path, which is in the shape of an ellipse, with the Earth being one focus. When the Moon is closer to the Earth, the point on the lunar orbit is called perigee, appearing larger. Conversely, when it is farther away, this position is called apogee.
Moon Phases: The light emitted by the Moon is called Earthshine. This light is generated by the reflection of sunlight on the Moon’s surface, causing the various moon phases. The lunar phases are four and succeed each other approximately every seven days. When there is one day left until the full moon, the lunar surface is almost completely illuminated, which is referred to as gibbous.
Solar Eclipse: This occurs when the Moon comes between the Earth and the Sun, producing a cone of shadow that darkens the Earth’s surface. When the Moon completely blocks sunlight, it results in a total solar eclipse. If it only covers a portion of the Sun, it is called a partial solar eclipse.
Tides: The daily rise and fall of sea levels are due to the gravitational forces of the Sun and Moon. Tides are caused by both the Sun and the Moon. When the sea level rises, it is known as high tide, and when it falls, it is called low tide. When the Sun and Moon are aligned, they produce the highest tides, known as spring tides or syzygies. Conversely, when the waning Moon or crescent is not aligned with the Sun, it results in the lowest tides, called neap tides or square tides.
Lunar Eclipse: This occurs when the Earth is positioned between the Sun and the Moon, producing a cone of shadow that prevents sunlight from reaching the Moon, resulting in a lunar eclipse.
Lithosphere: Earth Structure
Core: Located at the center of the Earth, the core is composed of iron and has two parts: the inner core, which behaves as a solid, and the outer core, which is in a liquid state. This allows for the flow of materials that generate the Earth’s magnetic fields.
Mantle: Surrounding the core, the mantle consists of semi-siliceous materials. It has an inner layer called the asthenosphere, which exhibits slow circular movements corresponding to the convective cells produced by high core temperatures. The outer layer of the mantle, near the crust, is called the lithosphere.
Crust: The rocky layer that surrounds the mantle has a thickness of 5 km on the ocean floor and 20 to 45 km on the continents.
Theories of Lithosphere Formation:
- Continental Drift Theory: This theory posits the existence of a large continent called Pangaea, which was surrounded by the great ocean Panthalassa. Pangaea split into Gondwanaland (southern hemisphere) and Laurasia (northern hemisphere), which began to move to their current positions over a process that lasted 300 million years. Evidence supporting this theory includes the observation that the coasts of Brazil and the western coast of Africa fit together like pieces of a puzzle.
- Theory of Ocean Floor Expansion: This theory shows that inter-oceanic ridges or ridges deliver volcanic magmatic material for the formation of new rocks.
- Theory of Plate Tectonics: This theory states that the Earth’s crust is fractured into plates that float on the asthenosphere, with mantle convection movements causing their displacement. The circular motions of the mantle generate convective cells. The heat from the core creates magma, which interacts with the crust and causes plate shifts.
Types of Plate Boundaries:
- Divergent Boundaries: Where magma emanates.
- Convergent Boundaries: Areas where one plate sinks beneath another, leading to high seismic and volcanic activity.
- Transform Boundaries: Where two plates move parallel to each other, generating seismic activity due to friction.
Volcanic Activity: This involves the expulsion of liquid magma and incandescent materials accumulated in the magma chamber through chimneys, cracks, or fissures in the crust, resulting in eruptions. When magma comes into contact with the atmosphere, it is called lava, which flows from the crater down the slopes of the volcano.
Seismic Activity: The violent movements of the crust, lasting from a few seconds to three minutes, are called earthquakes. Earthquakes originate inside the Earth at the hypocenter or focus, with the first point where the seismic wave contacts the crust being the epicenter. There are two types of seismic waves: surface waves, which travel through the Earth’s crust, and body waves, which travel through the Earth’s interior. Body waves are further divided into primary (P) waves, which are the fastest and can pass through any material, and secondary (S) waves, which move up and down and are more destructive.
Mercalli Scale: This scale measures the intensity of earthquakes based on the damage to structures, considering the ground conditions and the quality and design of buildings.
Richter Scale: This scale classifies earthquakes by magnitude, measuring the amount of energy released during the breaking of rocks at the hypocenter. The largest recorded earthquake in the world occurred in Valdivia on May 22, 1960, with a magnitude of 9.5 degrees.