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What are the layers that make up the Earth?
What are the three main layers?
Earth’s Interior
three main layers
1. Crust
Outermost solid layer
Example:
Continental crust
Oceanic crust
2. Mantle
Thick middle layer
Example:
Upper mantle
Lower mantle
3. Core
Innermost hot layer
Example:
Outer core
Inner core
Fig. 2.1 — The Earth’s interior: crust, mantle and core
| Crust | Mantle | Core |
|---|---|---|
| It is the outermost layer | It is the middle layer | It is the innermost layer |
| Thickness: 30–40 km under continents, 5–7 km under oceans | Thickness: about 2900 km | Thickness: about 3450 km (outer core about 2200 km + inner core about 1250 km) |
| State: solid rock | State: mostly solid , but hot and able to flow slowly | State: outer core is liquid , inner core is solid |
- The Earth has three main layers .
- These are the crust , the mantle and the core .
- The crust is the outermost layer — we live on it.
- The mantle is the middle layer — very thick and hot.
- The core is the innermost layer — extremely hot and heavy.
Good to know
The core itself has two parts — a
fluid outer core
of iron and nickel, and a
solid, spinning inner core
that is the densest part of the Earth.
What is the lithosphere?
Lithosphere
Litho-
Greek for ‘rock’
-sphere
a ball-shaped layer
↓
The rigid outer layer made of the crust and upper mantle.
Definition — Lithosphere
The rigid outer layer of the Earth.
It is made of the crust and the upper part of the mantle.
It is broken into tectonic plates.
It is made of the crust and the upper part of the mantle.
It is broken into tectonic plates.
What is the asthenosphere?
Asthenosphere
Astheno-
Greek for ‘weak’
-sphere
a ball-shaped layer
↓
The soft layer below the lithosphere that permits plate movement.
Definition — Asthenosphere
The soft, semi-molten layer just below the lithosphere.
It is the lower part of the mantle.
It lets the tectonic plates move slowly over it.
It is the lower part of the mantle.
It lets the tectonic plates move slowly over it.
Which layers make up the lithosphere and the asthenosphere?
How do the two outer zones differ?
Outer Earth Layers
two contrasting zones
1. Lithosphere
Rigid outer shell
Contains the plates
Example:
Crust
Upper mantle
2. Asthenosphere
Soft layer below
Lets plates move
Example:
Lower mantle
- The crust and the upper part of the mantle together form the lithosphere .
- The lower part of the mantle forms the asthenosphere .
- The core (inner core and outer core) lies deep below both of them.
How the Layers Group into the Lithosphere and Asthenosphere
Crust
Mantle — upper part
Lithosphere
Mantle — lower part
Asthenosphere
Core — inner core
Core — outer core
Deep core (below both)
Difference between the Lithosphere and the Asthenosphere
Lithosphere
Asthenosphere
It contains the
crust
and the
upper part of the mantle
.
It contains the
lower part of the mantle
.
It is
rigid
and solid.
It is
soft
and semi-molten.
It
has tectonic plates
.
It
does not have tectonic plates
.
It does
not flow
; the plates rest on top of it.
It can
flow slowly
, which lets the plates move.
The rigid lithosphere above and the softer, semi-molten asthenosphere below
⚠️ Common Mistake
Plates do not float on
molten lava
, like boats on water. They rest on the asthenosphere, which is semi-molten — soft and mobile, not a liquid ocean of lava.
📝 What Have We Learned
- The Earth has three main layers : crust, mantle and core.
- The crust and the upper mantle together form the lithosphere .
- The lower mantle forms the soft asthenosphere .
- The lithosphere has tectonic plates ; the asthenosphere does not.
- The asthenosphere lets the tectonic plates move .
So the lithosphere is broken into
tectonic plates
, and the soft asthenosphere below lets them move. Let us now see what these tectonic plates actually are.
