Understanding Layer by Layer Structure of the Earth.
                     UNDERSTANDING LAYER BY LAYER 
STRUCTURE OF THE EARTH
Introduction
• There is more to the Earth than what we 
can see on the surface. 
• In fact, if you were able to hold the Earth 
in your hand and slice it in half, you'd see 
that it has multiple layers
Source: phys.org
Layers based on chemical 
composition
• During Earth’s early formation, the planet 
underwent a period of differentiation that 
allowed the heaviest elements to sink to 
the center and lighter ones to rise to the 
surface. 
• Earth’s internal layering can be defined by 
this resulting chemical composition. 
Source: wiki.seg.org
Main layers of Earth
• The three main layers of Earth include:
1.  the crust (1 percent of Earth’s volume) 
2. the mantle (84 percent)
3. the core (inner and outer combined, 15 
percent). 
Source: wiki.seg.org
Crust
• The solid crust is the outermost and 
thinnest layer of our planet. 
• The crust averages 25 miles (40 
kilometers) in thickness and is divided in 
to fifteen major tectonic plates that are 
rigid in the center and have geologic 
activity at the boundaries, such as 
earthquakes and volcanism.
Source: wiki.seg.org
Mantle
• Mantle material is hot (932 to 1,652 
degrees Fahrenheit, 500 to 900 degrees 
Celsius) and dense and moves as semi-
solid rock. 
• The mantle is 1,802 miles (2,900 km) thick 
and is composed of silicate minerals that 
are similar to ones found in the crust, 
except with more magnesium and iron 
and less silicon and aluminum.
Source: wiki.seg.org
Outer Core
• The outer core is composed mostly of iron 
and nickel, with these metals found in 
liquid form. The outer core reaches 
between 7,200 and 9,000 degrees 
Fahrenheit (4,000 and 5,000 degrees 
Celsius) and is estimated to be 1,430 miles 
(2,300 km) thick. 
• It is the movement of the liquid within the 
outer core that generates Earth’s magnetic 
field.
Source: wiki.seg.org
Inner Core
• The inner core is the hottest part of our 
planet, at temperatures between 9,000 
and 13,000 degrees Fahrenheit (5,000 and 
7,000 degrees Celsius). 
• This solid layer is smaller than our Moon 
at 750 miles (1,200 km) thick and is 
composed mostly of iron. 
• The iron is under so much pressure from 
the overlying planet that it cannot melt 
and stays in a solid state.
Source: wiki.seg.org
Layers based on 
physical properties
Lithosphere
• The lithosphere is the outermost layer of 
the Earth ~100 km thick and is defined by 
its mechanical properties. 
• This rigid layer includes the brittle upper 
portion of the mantle and the crust. 
Source: wiki.seg.org
Asthenosphere
• The asthenosphere includes the upper 
part of the mantle that is highly viscous 
and mechanically weak. 
• The lithosphere-asthenosphere boundary 
(LAB) is where geophysicists mark the 
difference in ductility between the two 
layers.
Source: wiki.seg.org
Mesosphere
• The mesosphere refers to the mantle in 
the region under the lithosphere and the 
asthenosphere, but above the outer core. 
• The upper boundary is defined as the 
sharp increase in seismic wave velocities 
and density at a depth of 660 kilometers 
(410 mi). 
Source: wiki.seg.org