Traditionally, when we talk about the layers of our planet we talk about the inner core, outer core, mantle, and crust.

But when we talk about Plate Tectonics we have to deal with another concept  – that is the lithosphere.

What is the Lithosphere?

The lithosphere is defined as the outermost rigid rocky layer of the Earth and it is made up of the crust and the top brittle section of the mantle.   The Earth’s tectonic plates are ‘slabs’ of the lithosphere.

The upper part of the lithosphere is the crust – which can be divided up into oceanic crust or continental crust.  Oceanic crust is made up of the rock types basalt and gabbro and the continental crust is made up of a mix of all the igneous, sedimentary and metamorphic rocks. (You can find out more about the crust here)

Underlying the crust is the brittle part of the mantle which is made up primarily of the rock type peridotite.  This is a very dense ultrabasic igneous rock made up of the minerals olivine and pyroxene.  Sometimes pieces of peridotite are brought to the surface as chucks of materials in lava during a volcanic eruption.  This layer is found under both oceanic and continental crust making up those tectonic plates.

The boundary between the crust and the mantle layers of the lithosphere is called the Mohorovičić discontinuity – or just Moho for short.  This boundary was recognized by the difference in density and how it affected seismic waves.   In some amazing places on Earth where tectonic plates have collided so that the lower lithosphere has been thrust up to the surface and you can see the ancient Moho exposed.

The boundary between the dark rocks on the right and the lighter rocks on the left is an ancient exposed Moho in Italy.

So what about the Asthenosphere?

The Asthenosphere is the semi-molten weak layer of the upper mantle that lies directly below the lithosphere.  It may be around 2-4% molten and the rest is a ‘plastic’ layer that is ductile and weak.  It is on this layer that the tectonic plates ‘slide’.





What is the Lithosphere?

Traditionally, when we talk about the layers of our planet we talk about the inner core, outer core, mantle, and ...
Read More

Introduction to Plate tectonics

Learn the basics of the theory of Plate Tectonics in less than 10 minutes!   Why do earthquakes and volcanoes ...
Read More

Lava in Lihue – Role play activity

Description : A classroom role-play activity where students play the role of various town people when their town is being ...
Read More

Rocks of Ages

Description : Student activity where they calculate the speed of a moving tectonic plate by using the ages of rocks ...
Read More

Understanding Polar Reversals

Understanding polar reversals helps us to understand an important piece of evidence for Plate Tectonics. When molten rock cools, some ...
Read More

Divergent Plate Boundaries

One of the most amazing places on the Earth's is where two massive tectonic plates are moving apart.  Almost 99% ...
Read More

Evidence for Plate Tectonics

The evidence for Plate Tectonics is very conclusive.  It is a very well supported theory, and while scientific debate continues ...
Read More

Boundaries – how the plates interact

The Earth's plates don't just sit there.  They move and interact at their boundaries - and that is what makes ...
Read More

Plates – understanding the tectonic jigsaw pieces.

The Earth's rocky outerlayer (the lithosphere) is broken up into around seventeen major pieces that we call tectonic plates.   ...
Read More

The Earth’s Crust – a simple way to view it.

The Earth's crust - that outermost rocky layer of our planet - can be daunting to understand.   To start ...
Read More


What is the Lithosphere?

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.