Earth's Structure and Plate Tectonics: A Deep Dive

Seismic Discontinuities and Earth's Layers

Seismic discontinuities are abrupt changes indicating a seismic wave entering a new material or a material with a different viscosity. These discontinuities reveal Earth's layered structure, primarily the core, mantle, and crust.

Plate Tectonics: Unifying Earth's Processes

Initially, phenomena like mountain formation, volcanoes, earthquakes, and mineral deposits were studied independently. Around 1960, relationships between these aspects led to the development of the theory of plate tectonics, supported by substantial evidence.

Catastrophism vs. Uniformitarianism

Catastrophism proposed that Earth's relief was formed by sudden catastrophic events. In contrast, Uniformitarianism suggests that current geological processes, their rates, and governing laws are the same as in the past, with planetary conditions remaining consistent despite changes.

What is Plate Tectonics?

Plate tectonics can be summarized in three key points:

• The Earth is divided into rigid lithospheric plates.
• These plates are not static; they slowly change in size, shape, and position.
• This dynamic movement produces titanic clashes between plates, triggering various internal geological processes.

Plate Boundaries and Interactions

Lithospheric plates move in relation to each other, interacting through separation, collision, or lateral sliding, causing ground changes.

Boundaries are classified as:

• Convergent boundaries: where plates collide.
• Divergent boundaries: where plates separate.
• Lateral motion boundaries: where plates slide past each other.

Interactions at Plate Boundaries

• Oceanic-Oceanic Convergence: The older, denser plate subducts into the mantle, causing intense submarine volcanism and fewer strong earthquakes.
• Oceanic-Continental Convergence: The denser oceanic plate subducts under the continental plate, deforming it and creating mountain ranges parallel to the convergent edge.
• Continental-Continental Convergence: Collision between two continental plates results in the formation of orogenic collision ridges, as neither plate subducts due to low density.

Divergent Boundaries and Ocean Formation

When divergent boundaries form within a continent, Rift valleys, large elongated depressions, are created. If these valleys connect with an ocean, they flood, forming a sea. The lithosphere will develop a dorsal ridge with intense volcanism.

Evidence Supporting Plate Tectonics

• Paleoclimate Evidence: Glacial deposits found on multiple continents indicate a major glaciation 300 million years ago.
• Paleontological Evidence: Fossils found on separate landmasses suggest they were once part of the same landmass.
• Paleomagnetism: Minerals in cooling lava align with the magnetic pole at the time, proving that continents have moved.