The study of Earth's internal layers, specifically the lithosphere and the underlying asthenosphere, is fundamental to understanding plate tectonics. The movement of tectonic plates is driven by convection currents within the mantle, which are directly influenced by the thermal structure and composition of the Earth's interior. Therefore, grasping the internal structure provides the necessary context for explaining how and why plates shift, collide, and diverge across the globe.

The Earth's lithosphere is divided into tectonic plates, which are broadly categorized into two types: continental plates and oceanic plates. Continental plates are primarily composed of granitic rocks and are thicker and less dense, while oceanic plates are composed of basaltic rocks, making them thinner and denser, which influences their behavior at plate boundaries.

The Earth's lithosphere is broken into several large and small sections known as tectonic plates. These plates float on the semi-fluid asthenosphere beneath them. The movement and interaction of these plates at their boundaries are responsible for major geological phenomena, including earthquakes, volcanic activity, and the formation of mountain ranges.

The San Andreas Fault is a famous transform plate boundary located in California, USA. It marks the sliding contact between the Pacific Plate and the North American Plate. This strike-slip fault is responsible for significant seismic activity in the region as the two massive tectonic plates grind past each other horizontally over millions of years.

Mid-ocean ridges are extensive underwater mountain ranges formed by plate tectonics. These volcanic systems are continuous and span tens of thousands of kilometers across the ocean floor, making them significantly longer than any individual fold mountain range found on the Earth's continents.

Transform plate movement occurs at transform boundaries where plates slide laterally past one another. Unlike convergent or divergent boundaries, crust is neither created nor destroyed at these locations. The friction between these plates often leads to significant seismic activity as energy is released.

At divergent plate boundaries, the lithosphere pulls apart, reducing pressure on the underlying mantle. This causes decompression melting, allowing magma to rise. Once this molten rock reaches the Earth's surface, it is referred to as lava.

A divergent plate boundary occurs where two tectonic plates move away from each other. The separation of the South American Plate and the African Plate is a primary example, which led to the formation of the Mid-Atlantic Ridge. As the plates pull apart, magma rises from the mantle to create new oceanic crust, continuously widening the Atlantic Ocean floor.

The Nazca Plate is an oceanic plate that is denser than the continental South American Plate. When they converge, the Nazca Plate is forced downward into the mantle beneath the South American Plate in a process known as subduction. This interaction is responsible for the formation of the Andes Mountains and frequent seismic activity in the region.

The word 'tectonics' originates from the Greek word 'tekton', which translates to 'builder' or 'carpenter'. In the context of geology, the term refers to the large-scale processes that shape the Earth's crust, effectively 'building' the structural features of the planet's surface. Plate tectonics describes the movement and interaction of the lithospheric plates, which are the primary agents responsible for the formation of mountains, ocean basins, and volcanic activity throughout geological history.