Rock Types, Earth's Interior, and Plate Tectonics

Types of Rocks

Sedimentary: Rock formed by material eroded and transported by geologic agents, including sedimentary basins, which have been compacted over time.

Magmatic (Igneous): Originated by the cooling of a molten rock mass. There are two types:

• Plutonic: Cooling magma within the Earth's crust. They have a crystal texture.
• Volcanic: Rapid cooling of lava on Earth's surface. They have a microcrystalline texture.

Metamorphic: Rocks formed in the interior of the crust due to the high pressures and temperatures that produce changes in the minerals.

Definitions

Volcanism: The surface expression of rocks melting within the crust.

Earthquake: Brief and sudden movements of the Earth's crust.

Continental Drift: Slow, horizontal movement of continents.

Isostasy: Slow, vertical movements of the crust, which tends to sink in some places and rise in others.

Magma: Molten rock with dissolved gases. The most abundant gases are water vapor and carbon dioxide.

Lava: Molten rock that has lost its gas upon reaching the surface.

Hypocenter: The place where a fracture occurs.

Epicenter: The point where the earthquake is first felt and with the greatest intensity.

Seismic Waves: Vibrations transmitted from the seismic focus within the Earth.

Richter Scale: Indicates the amount of energy released at the hypocenter.

Seismographs: Apparatus that can record an earthquake and produce a graph showing its duration.

Seismograms: Allow us to interpret the way in which seismic waves have traveled across the globe.

Lithosphere: Rigid layer that is fragmented into large pieces; it includes the crust and upper mantle.

Lithospheric Plates: The huge pieces into which the lithosphere is fractured.

Geothermal Gradient: The increase in temperature from the Earth's surface into the interior.

Parts of the Earth

• Crust
• Mantle
• Outer Core
• Inner Core

Origin of the Earth's Internal Heat

The core has two parts: an external one that is molten and an internal one that remains solid due to extremely high pressures.

Pressure and Temperature Inside the Earth

Towards the interior of the Earth, not only does the temperature to which rocks are subjected increase, but so does the pressure.

Manifestations of Internal Heat

• Volcanism
• Earthquakes
• Continental Drift
• Isostasy

Internal heat also has other effects:

• Atmosphere: Formed from gases that escaped from the interior.
• Magnetic Field: Originates in the outer core.
• Hot Rocks: Found at shallow depths.
• Hydrothermal Phenomena: Water that seeps in through cracks in the crust comes into contact with rocks at high temperatures.

Volcanism

• Magma
• Lava

Volcanic Products

• Gas: The most common are water vapor and carbon dioxide.
• Liquids: The most fluid lava has the highest temperature.
• Solids: Fragments of rocks that are thrown into the air.
  • Volcanic Bombs
  • Lapilli
  • Volcanic Ash

The Movements of Lithospheric Plates

Convection currents push the plates in three ways:

• Separation: When two plates separate, there is intense volcanism.
• Collision: If two plates collide, the denser and heavier one sinks below the lighter one.
• Sliding: If two plates slide laterally against each other, earthquakes occur.

Volcanoes, Earthquakes, and Plate Tectonics

Earthquakes and volcanoes are not distributed randomly on the Earth's surface, but are aligned, forming volcanic and seismic zones.

Plate Tectonics

The theory that explains the causes, mechanisms, and consequences of the movements of lithospheric plates.

Consequences of Plate Movements

• Seismicity: In areas where two plates collide.
• Volcanism
• Folding and faulting of rocks
• Formation of Reliefs