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Department of
(Assistant professor)
March 2017
1.1. Meaning and Scope of
Geomorphology
Geomorphology is the discipline, which studies these
landforms.
It is concerned with the description and the explanation
of surface configuration of the Earth, the processes
responsible for their formation, and their spatial and
temporal
distribution.
In the words of William D.Thornbury (1985),
geomorphology is the study of landforms, including
their classification, description, nature, origin,
development, and relationships to underling structures,
as well as the history of geologic changes as recorded
by these surface features.
What is the focus/scope of geomorphology?
Traditionally, geomorphology has been concerned with the
features associated with terrestrial environments.
Recently, however, it includes the study of all features
associated with both terrestrial and aquatic environments.
Geomorphology is interdisciplinary in the sense that it may be
approached for different reasons and for different applications
In the past, it used to focus on the classification and description
of landforms. While this is very important, however, it is also
necessary to know what processes, which shape these
landforms.
1.3. Geological time scale
• Is also known as Geo-chronology.
• It is the time scale which indicates the sequential order of
geological events. Geological time scale started with the
age of the earth (4.7 billion years). It is broken in to four
levels of detail: eons, eras, periods and epochs. Eons
are the longest intervals represented. There are four of
them: Hadean for which there is no rock recorded;
Achaean (for ancient), which offers little evidence of life
and surface conditions that were not yet Earth _like;
proterozoic (early life), in which conditions became
Earth_ like for the most part and in which different life
forms appear as fossils; and phanerozoic (apparent life)
which has abundant signs of life and in which we live.
The Precambrian Era is the name we give to the first three eons. It is the oldest and the longest eras. It
covers the whole time from the beginning of the Earth to the last 600 million years ago. Because most of
the features of this era are absent due to erosion and other Earth movements.
The oldest rocks of the continents and remnant features which today exist in the form of lower, rounded
hills (shields) in the interior of the continents must have been formed during this era. Most of the rocks
of this era are overlain by younger rocks formed during the succeeding eras and, thus are highly
metamorphosed and crystalline. Most of these rocks today are founded at base of other rocks and, hence,
are called basement complex rocks.
Hadean eon- Oldest part of Precambrian Era
Archean eon- Middle part of Precambrian Era
Praterozoic eon - (the suffix zoic indicates life); primitive fossils bacteria, algae and worms are
formed. it is the youngest part of Precambrian Era
Why not The Precambrian Era did not divided in to periods and epochs?
b/c of its remoteness, there was lack of evidence.
 The major geologic processes in Precambrian era are:
Orogenic processes (mountain Building process)
Faulting
Folding
Igneous activities
Finally erosion and deposition (denudation and peneplaination)
Huge mountains were layered (peneplained)
Peneplaination –sedimentation of different layers.
 The Hadean, Archean, and Proterozoic eons have not been separated into shorter time intervals
because of the relative absence of fossils.
• The time span from Cambrian period up to the present
is termed as Phanerozoic Eon.
• It is a Greek word w/c means visible life (abundant
life).
• The phanerozoic is broken in to three eras: the Paleozoic
(old life), Mesozoic (middle life), and Cenozoic (recent
life).
• The Paleozoic era, covering the time from about
580million to 240million years ago, is characterized by
denudation .It probably began with the appearance of
many different life forms, which today are preserved as
fossil in rock sequences all over the world. It ended with
the extinction of over 90% of all living organisms at the
end of the Permian period. The cause of this event is
currently unknown.
It is the oldest era of phanerozoic eon.
The second largest era in G.T.S.
Major geological events were:
The dominant processes were denudation(erosion), and peneplaination
(deposition)
There was climate change w/c resulted in intense erosion.
Former mountains were levelled
The coal formed during the carboniferous period(from the deposition of the
swamp vegetation) was eroded by intense erosion
Life forms of the era
Invertebrates were dominant
Single celled – protozoan existed
Fish appeared
Amphibians and reptiles roamed around the close of the era
The Mesozoic Era (the middle life) covers the geological history of
the Earth from about 240million to 70million years ago. It began with
the appearance of many new kinds of animals, including dinosaurs
and the ammonites, or extinct relatives of modern squid. It ended
with another extinction in which about 80% of all living organisms
died. This extinction may have been the result of a large asteroid
that crashed in to the Earth. Generally, it is the beginning of the
fragmentation and moving apart of the fragments of the Earth that
until then existed in the form of a single land mass surrounded by a
single water body.
It has three periods; the Triassic, Jurassic and Cretaceous.
In temperate regions it was dominated by glacier erosion.
Age of reptiles and dinosaurs
Birds and primitive animals
Gymnosperm were dominant trees
Dinosaur disappear at the end of this era due to cloudy and
cold conditions
The Cenozoic Era has two geologic periods, the Tertiary (65million to 1.6 million years before
present) and the Quaternary period (1.6 million years before present to the present). The tertiary
period must have been characterized by the continuation of plate movements, accompanied by
volcanic eruptions resulting in the formation of the major landforms we see on Earth today. The
quaternary period is the time we live in now and is basically characterized by denudation, mostly as
a result of moving water, ice and wind.
The well known and most recent era.
The periods are: Tertiary and Quaternary
Tertiary
Internal processes were dominant e.g Trapean Series Lava caused mountain building. Most
of the present land features are the resulting processes of cenozoic era.
In middle latitude
Ice age- glacier deposition also happened in the tropical highland like semen mountain, bale,
the valley covered by glacial deposits.
Tropical regions
Cold and high rainfall sometimes called pluvial rain ; pole glacial temperature decrease
Life forms - mammals are dominant
Flowering plants (angiosperm) flourished
Quaternary
Modern human history
youngest and Shortest
Paleocene: small mammals
Oligocene: big mammals
1.5. Dating methods
• How is the age of rocks or features’ or events
determined? Geologists can determine the age of rocks
in terms of absolute years, or in relation to the layers of
rocks around them. Thus, there two ways of expressing
the age rocks, namely relative and absolute.
1.5.1. Relative age dating
• Relative age refers to the age of rock with respect to an
other rock/features. Arranges events in order based on
places, or rocks in a sequence of order. It does not
indicate the exact age of the rock. In order to determine
the relative age of rock layers, scientist use the
following simple but internationally accepted
principles.
1. Principle of original horizontality: Sedimentary rocks are
deposited in nearly horizontal layers (beds).If layers are no
longer horizontal they must have undergone deformation after
formation.
• Sediment particles deposited from water under the influence of
gravity form essentially horizontal layers.”
• Sedimentary rocks are deposited in nearly horizontal layers.
The majority of sedimentary rocks are deposited under water.
They may be pushed above sea level and tilted during the
formation of mountains. These processes expose rocks to
weathering and erosion that serves to erase parts of the
geologic record as rock units are worn away.
2.
, which states that
younger beds of rock occur on top of older beds in
an undisturbed sequence of layers. When we
examine a series of undisturbed sedimentary rock
layers we assume the rocks at the bottom of the
stack are the oldest and the rocks at the top are the
youngest (Look the fig below) (also applies to
volcanic rocks).
Left: The principle of superposition tells us that the beds near the
river are older than the beds at the top of the slope.
Right: the layers are numbered from oldest (1) to youngest (4)
according to their sequence of formation.
3. The law of crosscutting relationships,
• States that any feature or structure that cuts through and disturbs
a rock sequence must be younger than the disturbed beds. If
igneous rocks cut across sedimentary layers; sedimentary rocks
there first, igneous rocks introduces later.
4. Principle of fossil correlation
• Fossils are remains of life forms. Sometimes called Principle of Faunal
Succession. Acc. To palaeontologists “Fossil organisms succeed one
another in a definite and determinable order, so any time period can
be recognized by its fossil content.” General pattern of development
is from simple to complex organisms
• … Studies using these principals have demonstrated that some rock
sequences may not represent continuous depositions, but rather are
characterized by distinct breaks in the geologic record.
Age of fish → Age of coal swamps → Age of reptiles → Age of
mammals
(→ the older to the recent order)
Limitation of fossil correlation
• It is used for sedimentary rock, not functioned for igneous and
metamorphic rocks.
1.5.2. Absolute age dating
Unlike relative dating, which relies on sequencing of rock
layers (i.e. younger vs. older), absolute dating can produce
an actual age in years. It involves laboratory work and is
most sophisticated.
Since the discovery of radioactivity scientists have been
able to determine numerical age of rock units. Radioactivity
provides a “clock” that begins working when radioactive
elements are sealed into newly crystallized minerals. The
rate at which radioactive elements decay can be measured.
Therefore, if we can determine the ratio of particular
radioactive element and its decay products in a mineral, we
can calculate how long ago that mineral crystallized.
Determining the age of rock through radioactive elements
is known as isotopic dating (previously and same what
inaccurately), called radiometric dating.
Radiometric Dating
•
Radiometric techniques were developed after the discovery of radioactivity in 1896. The regular rates of
decay for unstable, radioactive elements were found to constitute virtual “clocks” within the earth’s
rocks
It is based on some natural clocks.
•
•
Radioactive isotopes- elements that decay spontaneously by emitting radiation
The isotopes of a given element have different numbers of neutrons, but the same numbers of protons.
Uranium, for example commonly occurs as two isotopes, U-238 and U-235.The former has 238 protons
and neutrons in its nucleus, where as the later has 235.Of this particles, 92 (the atomic number of
uranium) must be protons and the rest neutrons.U-238weights slightly more than U-235).
Parent: a radioactive element that breakdown (decay).
Parent isotopes finally converted in to stable element called daughter isotopes
•
Half life: the time required to decay (disintegrated)
Each radioactive parent isotope decays to its daughter product at a specific and measurable rate. This
measurement is reported in half-lives. The half-life of an isotope is the time it takes for ½ of the parent
atoms in the isotope to decay.
If an isotope has a half-life of 4000 years, then after 4000 years ½ of the parent isotope remains. After
another 4000 years, ½ of ½ remains, or ¼ of the original amount of parent isotope. In another 4000
years (12,000 years total), ½ more of the remaining amount decays, so after 3 half-lives, there only
remains 1/8 (½ of ½ of ½) of the original parent isotope.
If a scientist knows the half-life of the parent and measures the proportion of parent isotope to daughter
isotope, he/she can calculate the absolute age of the rock. This valuable method is called radiometric
dating.
Define the term Geomorphology
What is the scope of Geomorphology in both
traditionally and recent approaches?
What is Geological time scale?
Distinguish eons, eras, periods & epochs.
How old is the earth (both in Geologic
estimation and creationist views)