Differentiation of earth

1. DIFFERENTIATION OF EARTH

2. CONTENTS
 Introduction
 Structure of the earth
 Differentiation of the earth
 When did differentiation happen?
 Homogeneous accretion
 Heterogeneous accretion
 Process of differentiation
 Sources of heat to melt earth
 Layers of the earth.
 Critical Evidence from the Moon
 Conclusions
 References

3. Introduction
 Earth is third planet from the sun it is the 5th
largest planet in the universe and the largest
terrestrial planet in the solar system in terms of
diameter, mass and density.
 Earth belongs to milky way galaxy, Local group
cluster or Virgo super cluster.
 Earth is the only place in the universe where life
is known to exist and in other planets of the solar
system.
 The planet earth formed about 4.6 billion years
ago in a fully molten state.

5. Differentiation of the earth
The materials making up the present- day solid earth are
not mixed together in a homogeneous mass. Rather they
arranged in a series of concentric layers of diffusing
density. The heaviest materials, molten metals, lie at the
center of the earth and are overlain by progressively lighter
layers of silicate minerals
Two general theories have been proposed to explain the
origin of Core-Mantle- Crust layering;
Homogeneous accretion
Heterogeneous accretion

6. When did differentiation happen?
About 4.5 billion years ago
After beginning of Earth’s accretion at 4.56 billion
years ago
Before the formation of the Moon’s oldest known
rocks, 4.47 billion years ago

7. Sources of heat to melt Earth
Frequent and violent impacts
There was likely one particularly large impact
Moon aggregated from the ejected debris
Earth’s spin axis was tilted
Decay of radioactive elements
This heat generation was greater in the past
than today

8. Homogeneous accretion
Homogenous accretion: Similar elements stick together,
creating a solid mass. The heat generated in this process
melts the particles. The heavier elements sink to the center
because of gravity, creating the Earth's solid core.

9. Heterogeneous accretion
About 4.6 billion years ago, the Earth formed as
particles collected within a giant disc of gas orbiting a star.
Once the sun ignited, it blew all of the extra particles away,
leaving the solar system. The exact process probably
included both homogenous and heterogeneous accretion.

10. PROCESSES OF DIFFERENTIATION
In a liquid or soft solid sphere,
denser material sinks to the center and less
dense material floats to the top.
When rock is partially melted, the
melt and the remaining solid generally have
different chemistry and density. The melt is
usually less dense than the “residue.” The melt
is enriched in “incompatible” elements. The
residue is enriched in “compatible” elements.

11.  Early earth heats up due to radioactive decay, compression and
impacts. Over time the temperature of the planet interior rises
towards the Fe-melting.
Fig : The earth heats up

12. 2) The iron “drops” follows gravity and accumulates towards the
core. Lighter materials, such as silicate minerals, migrate upwards in
exchange. These silicate-rich materials may well have risen to the
surface in molten form, giving rise to an initial magma ocean.
Fig 4: Descending iron drops and rising lighter material

13. 3) After the initial segregation into a central iron
(+nickel) core and an outer silicate shell,
further differentiation occurred into an inner
(solid) and outer (liquid) core (a pressure
effect: solid iron is more densely packed than
liquid iron), the mantle (Fe+Mg silicates) and
the crust (K+Na silicates). Initially large
portions of the crust might have been molten-
the so called magma ocean. The latter would
have cooled to form a layer of basaltic crust
(such as is present beneath the oceans today).
Continental crust would have formed later. It
is probable that the Earth’s initial crust was
remelted several times due to impacts with
large asteroids.
Fig : Differentiated Earth

14. Layers of the earth.

15. Contd..
Layer Relative position Density (in
grms/cubic cm
Composition
Crust Outermost layer;
thinnest under the
ocean, thickest
under continents;
crust and top of the
mantle called the
lithosphere
Oceanic crust
(3-3.3)
Continental crust
(2.7-3)
Solid rock- mostly
silicon and oxygen
oceanic- crust
basalt;
Continental crust-
granite
Mantle Middle layer, thickest
layer; top portion
called the
asthenosphere
Mantle
(3.3-5.7)
Hot softened rock;
contains iron and
magnesium
Core Inner layer, consists
of two parts- outer
core and inner core
Outer core
(9.9-12.2)
Inner core
(12.6-13.0)
Mostly iron and
nickel; outer core-
slow flowing liquid,
inner core, solid

16. Critical Evidence from the Moon
No direct data are available from the first 600 m.y. of earth history this can only be evaluated from
information available at present on the possible evolution of the other members of the solar system,
particularly the Moon. So the evidences obtained from the moon are critical.
1) After fragments of anorthosite were found in the regolith and identified as originating in the
highlands, it becomes clear that the moon had differentiated early to form a highland shell of
anorthosite gabbroic composition. This is required that an outer shell of the primitive moon
had been melted to yield the observed thickness of the anorthosite shell.
2) The second reason is that the record of lunar events are between 4400 and 3200m.y. this is in
marked contrast with the earth where knowledge of this period is restricted to fragmentary out
crops of rock dating back only to about 3800 m.y.
3) Thirdly, evidence for a completely molten early moon is provided by the lunar gravitational
and magnetic data. Till recently there has been no strong evidence for an iron core in the moon.

17. Conclusions
The earth is a part of our Solar System, consisting of the Sun, nine planets, the
asteroid belt, and occasional comets. After the Earth was formed, there were many
planetesimals still in the Solar System. These bombarded the Earth in what is called the
Great Bombardment, which was so intense that the Earth's temperature increased
significantly. In such a state, differentiation occurred, in which the heavier elements, such
as iron and nickel, sunk to the center, and the lighter elements floated to the top. This led
to a layered structure of the Earth. These layers are grouped as follows:
 Inner Core: The inner core, about 1200 km thick, consists of mainly iron and nickel in a
molten state due to the intense heat and pressure.

18. Contd..
 Outer Core: The outer core is about 2300 km thick, and consists also mainly of nickel
and iron, but in a solid form.
 Mantle: The mantle, about 2900 km thick, is rich in lighter elements such as oxygen,
silicon, magnesium, and iron.
 Crust: The crust is composed of the lightest elements of the earth, and varies in
thickness from about 10 km beneath the oceans to about 70 km thick beneath the
continents.
The earth heated up by a combination of three processes of Radioactive decay of U. Th
and K, Gravitational compression and Meteorite impacts.

19. References
 Don L. Eicher (1980), History of earth, Prtice;Hall, Inc Pp 8-26.
 M.W.Mc Elhilly (1979), The earth its origin, structure and
evaluation, Academic Press London Ltd. Pp 2-53.
 C.M.R Fowler(1990), The solid earth, Cambridge university
press,Pp 4-30
Internet Sources:
 www.google.com
 www.Wikipedia.com