Earth's Formations and Layers

4. Step 1: accretion of
cm sized particles.
countless numbers
of these small
particles collide at
low relatively
velocity and
coalesce into
objects which are a
few km in diameter

5. Step 2: Physical
Collision on km
scale. once these
km size objects are
formed, they start
to smack into one
another and stick
thus creating fewer
new objects of size
10-100 km

6. Step 3: Gravitational
accretion on 10-100 km scale.
Once an object gets to a
radius of 10-100 km, its cross
section is larger than its
physical cross section
because it exerts a
gravitational influence on
surrounding smaller bodies
and, in essence, sweeps them
up. This process will create a
planet with significant gaps
between each swept up zone.

7. Step 4: Molten protoplanet
from the heat of accretion . For
each protoplanet that forms,
there are thousands of left
over planetisimal objects.
These planetisimals are then
accelerated by the relatively
large mass of the formed
planets and they start to move
at high velocity throughout the
inner solar system - many of
them ultimately impact the
surfaces of the cooling planets.

9. Core: Inner and Outer
• The study of earth’s history interior is most
difficult because it is inaccessible. The
information about Earth’s core is from
seismic information and computer models.
• Inge Lehmann, a seismologist, discovered in
1936 that earth has solid inner core.
• Studies showed that the hot spherical solid
has a radius of 1250 kilometers.

10. • It consist mainly iron-nickel alloy and is
magnetic
• It has temperature of about 6000°c, amost
as hot as the surface of the sun.
• The pressure in the inner core is so great
that the alloy cannot melt. For this reason,
the inner core is mostly solid.

11. • The outer core is made mostly of iron and
nickel.
• The outer core is approximately 2300 km
thick.
• It is very hot; the temperature is between
4000°c to 5000°c . Because of the very high
temperature, the outer core is liquid.
• The boundary between the outer and inner
core is sometimes referred to as Lehmann
discontinuity.

12. Inner Core and outer Core
Inner Core
Iron and nickel
Magnetic
Solid
1250 km
Outer Core
Iron nickel
Magnetic
Liquid
2300km
Cause of Earth’s
magnetic field
Earth’s molten metallic core gave rise to magnetic field.
The magnetic field is attributed to the dynamo effect of
circulating electric current.

13. Mantle: Lower and Upper

14.  The mantle is the longest part of the Earth.
 It is the intermediate layer of Earth and is
subdivided into lower and upper mantle.
 It is made up of molten rocks called magma.
 The magma circulates in currents determined
by the cooling and sinking of heavier
minerals, and the heating and rising of the
lighter minerals.
 The mantle has a total thickness of 2900km.

15.  The lower mantle is hot and exhibits plasticity.
The higher pressure in the layer causes of
formation of minerals that are different from
that of upper layer.
 Gutenberg discontinuity is detected between
Earth’s lower mantle and the outer core
observed by changes in the seismic waves. I
 It is 2240 km thick.

16.  The uppermost mantle and earth’s crust that form the
lithosphere are relatively rigid.
 The upper boundary that separates the upper mantle
from earth’s crust is defined by the sudden increase in
seismic velocity.
 This is called Mohorovičić (or Moho) discontinuity, as
noted by Andrija Mohorovičić
 In 1909.
 Moho is 5km below the ocean floor and 20 to 90 km
wit an average of 35km, beneath typical continents.

18.  The name was given by British geologists Joseph
Barell in 1914.
 The balance between temperature and pressure
is so great that the rocks have a little strength
(weak) and are easily deformed.
 It is believed that asthenosphere plays a critical
role in the movement of plates on the surface of
earth according to the plate tectonic theory.

21. Lower and Upper Mantle
Lower/ Mid- Mantle
 Asthenosphere
 Soft/ magma
 Exhibits “plasticity”
 Convection currents
 2240 km
Upper Mantle
 Lithosphere
 Rigid/ solid
 Moho boundary
 660km

22. Crust
• There are two types of crust that make up
the surface of the lithosphere. These are the
oceanic crust and the continental crust.

23. Oceanic Crust and
Continental Crust
Oceanic Crust
Dark- colored
Rock sample:
basalt
More dense
50km
Continental Crust
Light- colored
Rock sample-
granite
Less dense
Coarse- textured
Thick layer
40-70 km