The Lithosphere– Asthenosphere boundary is defined by a difference in response to stress. the lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plastic deformation.

1. The lithosphere is a solid part of the earth.
2. Present lithosphere evolved due to the process of differentiation. 
3. The separation of lighter materials and denser materials is called the process of differentiation
4. The thickness of the lithosphere is thus considered to be the depth to the isotherm associated with the transition between brittle and viscous behavior.
5. The temperature at which olivine becomes ductile (~1000 °C) is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle.
6. The lithosphere is subdivided horizontally into tectonic plates, which often include terranes accreted from other plates. 

In Earth’s layer formation and the process of differentiation happened in two stages:

• In the first stage, a gradual increase in the density inside the earth leads to a rise in temperature. As a result, materials inside the earth started getting separated based on the density; heavy materials such as Iron sink towards the core and lighter materials such as Silicon and Aluminium moves towards the surface. This led to the development of the outer surface is called the crust.

• In the second stage, during the formation of the moon and due to giant impact, the earth was further heated up and the process of differentiation happened again which leads to the creation of three-layer that is crust, mantle, and core.

Formation of the Lithosphere: Birth of Earth’s Crust

The lithosphere originated billions of years ago through a process known as accretion. As Earth formed from a protoplanetary disk, solid materials began to coalesce, gradually building up the early crust. Over time, volcanic activity and intense heat caused the differentiation of Earth’s layers, leading to the formation of the lithosphere as the rigid outer shell.

Plate Tectonics: The Engine of Lithospheric Evolution

Plate tectonics, a fundamental geological process, plays a pivotal role in the evolution of the lithosphere. The lithosphere is divided into several large and small tectonic plates that float on the underlying semi-fluid asthenosphere. The movement and interactions of these plates give rise to various geological phenomena, including earthquakes, volcanic activity, and the creation and destruction of landforms.

Divergent Boundaries: Spreading the Lithosphere

At divergent plate boundaries, lithospheric plates move apart, creating new crust as magma rises from the mantle to fill the gap. This process, known as seafloor spreading, leads to the formation of oceanic ridges and the expansion of the lithosphere. Divergent boundaries also give rise to volcanic activity, contributing to the creation of new landforms.

Convergent Boundaries: Colliding and Subducting Plates

Convergent plate boundaries occur when two lithospheric plates collide. In these cases, one plate may subduct beneath the other, forming deep-sea trenches and volcanic arcs. Subduction zones play a crucial role in recycling lithospheric material back into the mantle. The collision of continents at convergent boundaries gives rise to mountain ranges and the uplift of land.

Transform Boundaries: Sliding and Faulting

Transform plate boundaries involve plates sliding past each other horizontally. These boundaries give rise to strike-slip faults, causing earthquakes as the plates release built-up stress. While no lithosphere is created or destroyed at transform boundaries, they contribute to the overall deformation and evolution of the lithosphere.

Evolution of Lithosphere,Evolution of Lithosphere

Read More : The Evolution Of The Earth