Palaeos:		Geosphere
THE EARTH		Structure of the Earth

In Geosphere is the solid or mineral part of the Earth, consists of layers, from the outer crust down to the inner core, which have separated through density and temperature.  Although it is impossible at present to sample the inner layers of the geosphere, indirect evidence is gained through studying the way earthquake waves pass through or are deflected in their passage through the earth.

There are two ways to classify the composition of the geosphere - chemically, into crust, mantle, and core, or functionally, in the case of the outer layers (crust and mantle) into lithosphere and asthenosphere.

Crust
The outermost layer of  the geosphere is called the crust, which is equivalent to the skin of an apple in thickness relative to the entire earth. Yet this thin tiny layer is what we think of as "the earth", with it's mountains, valleys, continents, ocean beds, etc.  The crust is rich in oxygen, silicon and aluminium, with lesser amounts of other elements like iron.  Owing to its low density (2.5 to 3.5 gm/cm³), the crust is able to float on the denser mantle.  The Earth's crust, as with many planetary crusts, is brittle and breaks relatively easily.

There are actually two types of crust, continental and oceanic.

Continental crust is made up of volcanic lava flows, huge granite blocks, and sediments laid down in shallow water or continental seas.  It is quite thick, averaging 30 to 40 km and beneath parts of mountain ranges reaching 80 km.  But it is made of lower density rocks, such as andesite and granite.

Oceanic crust is thin, only about 5 to 10 km deep, and made of relatively dense rock called basalt, possibly underlain by gabbro (a similar but coarser grained rock).  It also contains a greater proportion of magnesium.   The composition of the lower crust is not known, but it is probably gabbro.  Seismic waves pass through it at a more rapid rate than they do the upper crust.

Mantle
Beneath the crust is a complex middle region known as the mantle.  It is a broad layer of dense rock and metal oxides that lies between the molten core and the crust.  The mantle extends to a depth of about 2900 km and accounts for around 82% of the Earth's volume.  The mantle is thought to be made up mostly of peridotite, a type of rock composed of iron, magnesium, silicon, and oxygen.
Analysis of seismic waves show that the material that makes up the mantle behaves as a plastic - a substance with the properties of a solid but flows under pressure.  More precisely, the mantle consists of rigid and plastic zones.  The density of the mantle ranges from 3.5 to 5.8 gm/cm³.

Core
The core is composed of mostly iron and nickel and remains very hot, even after 4.5 billion years of cooling. Estimates of temperature are about 7000K (equal to the surface of a red dwarf), and having a density of around 14 gm/cm^3.  The core is divided into two layers: the liquid outer core and - at the Earth's center - the solid iron inner core.  Despite the tremendous temperatures this layer is solid due to the immense pressure of the overlying layers.  The inner core's radius is about 22% that of the overall Earth.

The sharp boundary between the crust and mantle is called the Mohorovičić discontinuity or Moho.  While the Gutenberg discontinuity seperates the mantle from the core.

Here is a diagram of the Geosphere according to the division of crust, mantle, and core:

This diagram is from the DINOSAURS AND THE HISTORY OF LIFE - GEOLOGY V1001x site
- Professor Paul Eric Olsen

 Lithosphere and Asthenosphere

• Lithosphere -  The lithosphere (from the Greek, λίθος, lithos, stone) is the rigid outermost layer of the geosphere.  The upper layer of the lithosphere is the crust.  Beneath the crust is a layer of rigid mantle.
• Asthenosphere.  Beneath the lithosphere is the molten plastic outer mantle of hot silicate rock.  Magma from the asthenosphere rises up in the form of volcanos.   The asthenosphere (from the Greek, ἀσθενής, asthenēs, devoid of force) is the part of the mantle that flows (called plastic behavior).   This can be compared to the movement of toothpaste in a tube.

Here is a diagram of the outer part of the Geosphere according to the Lithosphere and Asthenosphere:

this diagram is from VolcanoWorld

Plate Tectonics

Palaeogeography

plate tectonics and continental drift icons from This Dynamic Earth:The Story of Plate Tectonics, by W. Jaquelyne Kious and Robert I. Tilling, (on-line edition)