UCSB Science Line
This layer that maintains life on earth is called the lithosphere. The Lithosphere is composed of the crust and upper most solid mantle. While the Asthenosphere. The lithosphere is broken up into what are called tectonic plates. In the case of Earth, there are currently seven to eight major (depending on. The difference between asthenosphere and lithosphere is how the materials in these layers can flow. Rocks in the lithosphere are "rigid".
LAB depicts the transition from hot mantle in the asthenosphere to the colder and more rigid lithosphere above. The lithosphere is characterised by conductive heat transfer whereas the asthenosphere is a boundary with advective heat transfer [vii]. Seismic waves moving through the LAB, travel faster across the lithosphere than the asthenosphere. This is due to the different densities and viscosity of the asthenosphere.
What is the relationship between the lithosphere and the asthenosphere?
The boundary where seismic waves slow down is known as the Gutenberg discontinuity which is believed to be inter-related to the LAB, due to their common depths. Continental lithosphere LAB depths are a source of dispute, scientists estimate a depth ranging from km to km. Ultimately continental lithosphere and the LAB in some older parts, are thicker as well as deeper.
Suggesting that their depths are age dependant [viii].
Comparison of the Lithosphere and Asthenosphere Lithosphere The lithosphere concept was proposed in The asthenosphere concept was proposed in Lithosphere is composed of the crust and upper most solid mantle Asthenosphere is composed of the upper most weaker part of the mantle Lies beneath the atmosphere and above the asthenosphere Lies beneath the lithosphere and above the mesosphere The physical structure consists of a rigid outer layer that is divided by tectonic plates.
It is regarded as rigid, brittle, and elastic. This article focused on the first two layers, and their differences. Geology facilitates study surrounding some of humanities formidable issues, such as climate change, natural disasters tsunamis, earthquakes, volcanic eruptions, landslides, etc. The solutions to our current environmental challenges require a knowledge of our earth structures and systems. The depth of the lithosphere-asthenosphere transition varies widely throughout the Earth as it is dependent on the thermal regime.
The lithosphere may extend only 2 or 3 kilometers beneath young, hot, thin oceanic crust. However, beneath old, cool, thick continental crust, the lithosphere may be as thick as or even kilometers. The crust and the mantle, on the other hand, are layers of the Earth which are defined by chemical or compositional properties.
Specifically, the crust consists of less-dense crustal rocks e.
Oceanic crust is thin less than 10 kilometers while continental crust can be much thicker 70 kilometers or more. Geologists have actually never directly observed the crust-mantle boundary. No one has drilled a hole deep enough to reach the crust-mantle boundary. The deepest hole ever drilled on Earth is the Kola Superdeep Boreholewhich reached about 12 kilometers in depth. However, because this hole was drilled into thick continental crust, the hole came nowhere near the crust-mantle boundary.
However, other holes in other pats of the oceanic crust have almost— but not quite— reached the elusive mantle. As far as I know, no hole in either continental or oceanic crust has reached the crust-mantle boundary.
Geology Word of the Week: L is for Lithosphere - Georneys - AGU Blogosphere
Really, geologists have only scratched the surface of the planet. Since geologists cannot directly observe the crust-mantle boundary or, for that matter, the lithosphere-asthenosphere boundarythe boundary is defined by geophysical observations. The MOHO is a place where seismic P-waves suddenly increase in velocity, presumably because they are able to travel faster through the denser mantle rocks.
So, for those geology students about to take a test or a PhD qualifying exam, remember: The lithosphere is NOT the same as the crust. Rather, the lithosphere is comprised of both crust and upper mantle.