This document discusses the field of geology. It defines geology as the study of the Earth, including its physical and chemical properties from its creation to present day. The main branches of geology are described as crystallography, mineralogy, petrology, paleontology, and stratigraphy. The layers of the Earth are also summarized, including the inner core, outer core, mantle, and crust. Finally, several hypotheses for the origin of the Earth are outlined, such as the nebular hypothesis, planetesimal hypothesis, gaseous tidal hypothesis, and gas dust cloud hypothesis.

1. Geology
Dr.R.K.Kaleeswari
Professor (SS&AC)
Department of Soil Science & Agrl. Chemistry
TNAU, Coimbatore, India

2. GEOLOGY
Greek Earth The study of
Geology = The study of Earth

3. Geology : Definition
 Geology is the study of Earth, includes,
physical and chemical properties, earth
creation, inner and outer processes affected
it, since its creation to present day.

4. Branches of Geology
 Crystallography
 Mineralogy.
 Petrology .
 Paleontology .
 Stratigraphy .

5. Crystallography
 Crystallography is the experimental
science of determining the arrangement of
atoms in the crystalline solids

6. Mineralogy.
 Mineralogy is a subject of geology
specializing in the scientific study of
chemistry, crystal structure, and physical
(including optical) properties of minerals.

7. Petrology
 Petrology (from the Greek πέτρα, petra, "rock" and
λόγος, logos, "study") is the branch of geology that
studies the origin, composition, distribution and
structure of rocks.
 lithology focuses on macroscopic hand-sample or
outcrop-scale description of rocks petrography is the
speciality that deals with microscopic details

8. Paleontology
 the study of fossils to determine organisms'
evolution and interactions with each other
and their environments

9. Stratigraphy
 a branch of geology which studies rock
layers (strata) and layering (stratification).

11. INNER CORE
 HOT!!!! –
Thought to be
as hot as the
surface of the
Sun!
 Solid
 Composed of
Iron and Nickel

12. OUTER CORE
HOT!
 (but not as hot as
the inner core)
Liquid
Composed of Iron
and Nickel

13. MANTLE
 Still hot! – but
not as hot as
the core!
 Largest layer
 Composed of
various
materials
 Solid and liquid

14. CRUST
Cool
What we live on
Composed of
rocks, various
materials make up
the crust
Solid or Liquid?

15. Origin of earth
 About 4.5 billion years ago, Earth formed out of
nebula of gases and dust that were to become the
solar system
 The earth is between 4.3 and 4.5 billion years old.
 Small objects called planetoids accreted or combined
together to build larger objects such as planets

16. Origin of earth
 Nebular Hypothesis
 Planetesimal Hypothesis
 Gaseous Tidal Hypothesis
 Binary Star Hypothesis
 Gas Dust Cloud Hypothesis

17. Nebular Hypothesis
• German philosopher, Kant and French
mathematician, Laplace
• Earth, planets and sun originated from
Nebula.
• Nebula was large cloud of gas and dust. It
rotates slowly.

18. Nebular Hypothesis
 Gradually it cooled and contracted and its speed
 increased.
 A gaseous ring was separated from nebula
 Later the ring cooled and took form of a planet
 On repetition of the process all other planets came
 into being
 The central region, nebula became sun.

19. Objections
 Sun should have the greatest angular
momentum because of its mass and situated in
the center, however, it has only two percent of
momentum of the solar system
 How the hot gaseous material condensed in to
rings

20. Planetesimal Hypothesis
 Chamberlin and Moulton proposed the theory in 1904
 The sun existed before the formation of planets
 A star came close to the sun.
 Because of the gravitation pull of the star, small gaseous
bodies were separated from the sun
 These bodies on cooing became small planet's
 During rotation the small planets collided and form planets

21. Objections
 The angular momentum could not be
produced by the passing star.
 The theory failed to explain how the
planetesimals had become one planet

22. Gaseous Tidal Theory
 Jeans and Jeffrey proposed the theory in 1925
 Large star came near the sun.
 Due to gravitational pull a gaseous tide was
raised on the surface of the sun.

23. Gaseous Tidal Theory
 As the star came nearer, the tide increased in size.
 Gaseous tide detached when star move away.
 The shape of the tide was like spindle.
 It broke into pieces-forming nine planets of the solar
system

24. Binary Star Hypothesis
 The idea was developed by Lyttleton in 1938.
Before the formation of planets, the sun had a
companion star.
 Another star passed close to these double
stars and dragged the companion star away.

25. Binary Star Hypothesis
 A gaseous filament was torn from the
companion star and it remained close to the
sun.
 The planets were originated from this gaseous
filament in the same way as described in the
gaseous tidal hypothesis.

26. Gas Dust Cloud Hypothesis
 This hypothesis is due to C. Von Weizsacker
and O. J. Schmidt (1943).
 In this hypothesis the planets are thought to
have evolved out of a cold cloud of gas and
dust which was present around the sun.

27. Gas Dust Cloud Hypothesis
 It was called a “proloplanetary cloud”. Its shape
was like a disc.
 Planets were formed in this cloud by gradual
aggregation of the dispersed matter.
 This hypothesis explains well some of the
observed phenomenon relating to the solar
system.

28. Thank you