How Did the Lithosphere & Asthenosphere Form?

Lithosphere

• The lithosphere differs from the asthenosphere in its physical and mechanical properties, as it is a rigid shell. The asthenosphere by contrast is a thick fluid. The lithosphere consists of two separate parts, the continental and the oceanic lithospheres, which consist of different materials. The continental lithosphere was created through the process known as melting zones, while the oceanic lithosphere developed as the bottom of the ocean spread and more material was brought up to the crust.

Oceanic Lithosphere

• The ocean floor consists of rocks called basalt. These rocks typically do not exceed 1 billion years of age, because the molten material that pushes up from the mantle renews the oceanic crust on an ongoing basis. Molten rocks that were forced up from deep in the earth's mantle initially created the oceanic lithosphere.

Continental Lithosphere

• The crust of the continental lithosphere consists largely of granite rocks and is made up of elements such as sodium and potassium. Quartz and feldspar are the main minerals involved, while muscovite or biotite is also present. The continental lithosphere formed when magma solidified within the earth's crust. Granite forms as this magma begins to solidify. The granite, which is igneous rock, dates back about 3.8 billion years.

Asthenosphere

• The asthenosphere formed from molten matter that originated in the earth's core. Due to the pressure and temperature in the asthenosphere, rocks are easily deformed, like warm tar. Scientists refer to this section of the earth's mantle as the "low velocity zone" because seismic waves are slowed down when they pass through, due to its slushlike composition. The asthenosphere makes up only 6 percent of the mantle, but moves sufficiently to cause movement in the lithosphere layer as well. The weaker mechanical properties attributed to the asthenosphere are a result of its temperature, which is close to the melting temperature in the earth's core. In localized areas of the asthenosphere, melting occurs and gives rise to magma.