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The Earth's lithosphere is divided into tectonic plates, which are in constant motion due to the heat and convection in the underlying asthenosphere. The movement of these plates leads to the formation of various types of plate boundaries, which are classified as divergent, convergent, and transform boundaries.

The lithosphere is formed at divergent plate boundaries, where the plates move away from each other. This process is called seafloor spreading, leading to the formation of new oceanic crust as molten material (magma) rises from the asthenosphere to fill the gap between the separating plates. As the magma cools down and solidifies, it forms new lithosphere. A well-known example of a divergent boundary is the Mid-Atlantic Ridge.

The lithosphere disappears into the asthenosphere at convergent plate boundaries, where the plates are moving towards each other. There are three types of convergent boundaries: 1. Oceanic-Oceanic Convergence: When two oceanic plates converge, one of the plates subducts or sinks into the asthenosphere beneath the other plate, creating a deep-sea trench. The subducting plate melts as it descends into the asthenosphere, eventually forming new magma that can rise and lead to the formation of volcanic island arcs. An example of this process is the Marianas Trench in the Pacific Ocean. 2. Oceanic-Continental Convergence: When an oceanic plate converges with a continental plate, the denser oceanic plate subducts beneath the less dense continental plate. The subducting plate melts as it descends into the asthenosphere, creating new magma that can rise and create volcanic mountain ranges on the continental plate. The Andes mountain range in South America is an example of this process. 3. Continental-Continental Convergence: When two continental plates converge, they collide and can create massive mountain ranges, such as the Himalayas. In this case, there is no subduction of the lithosphere into the asthenosphere, as both continental plates are of similar density.

At transform plate boundaries, two plates slide past each other horizontally. No lithosphere is created or destroyed at these boundaries. Earthquakes are common along transform boundaries due to the friction between the sliding plates. The San Andreas Fault in California is an example of a transform boundary. In summary, the lithosphere is formed at divergent plate boundaries where seafloor spreading occurs and disappears into the asthenosphere at convergent plate boundaries where subduction takes place. No lithosphere is created or destroyed at transform boundaries.