EXOGENIC and ENDOGENIC PROCESSES
Ms. Macylaine Kate D.R. Siglos
Earth & Life Science Teacher
Learning Competencies:
At the end of the lesson, you are expected to:
Describe how rocks undergo weathering.
Explain how the products of weathering are carried away by
erosion and deposited elsewhere.
Describe where the earth’s internal heat comes from.
Describe how magma is form (magmatism)
Describe what happens after the magma is formed (plutonism &
volcanism)
Describe the physical and chemical changes in rocks due to
changes in pressure and temperature (metamorphism).
Compare and contrast the formation of the different types of
igneous rocks.
Compare & contrast the formation of the different types of
igneous rocks.
Geologic Processes on Earth
The dynamism of Earth is attributed to its
never ending geologic processes driven by
internal and external forces. Geologic processes
are broken down into two categories: exogenous
(external) and endogenous (internal).
EXOGENOUS PROCESSES
The exogenous processes occur on or near the
surface of Earth. They are usually influenced or driven
by gravity, water, wind, and organisms. These could be
destructive occurrences that leave significant changes
on the landscape and even in the ecosystem of an area,
in extreme cases, exogenous processes can wipe out
majority of the organisms inhabiting that area.
The following are the different types of exogenous
processes:
1. Weathering
It is the integration of rocks, soil, and minerals
together with other materials through contact with
Earth’s subsystems. Weathering happens even
without movement or transportation (as opposed to
erosion that involves movement). The breaking down
of soil and happen in situ or on the spot.
Two important types of weathering exist:
a. Physical Weathering
Is the breakdown of rocks by mechanical forces
concentrated along rock fractures. This can occur
due to changes, whether sudden or not, in
temperature, pressure, etc. for example, soil cracks
because of extreme heat or drought. In some cases,
water, wind, or ice may abrade or scrape rocks or
soil.
b. Chemical Weathering
is the process by which rocks break down by chemical
reactions. In this process, new or secondary minerals
develop and sometimes replace the original properties of
the minerals in the original rock or soil. Oxidation (the
reaction of a substance with oxygen) and hydrolysis (the
chemical breakdown of a substance when combined with
water) are chemical processes that contribute to
chemical weathering.
2. Erosion
It is the process by which Earth’s surface is worn
away by wind, water, or ice. The process of erosion
moves rock debris or soil from one place to another.
Erosion takes place when there is rainfall, surface
runoff, flowing rivers, seawater intrusion, flooding,
freezing and thawing, hurricanes, wind, etc.
This refers to the movement of large masses of
materials (e.g., rock debris, soil, mud) down a slope or
a steep-sided hill or mountain due to the pull of
gravity. Mass wasting is very destructive in areas
with increased water flow (such as rainfall or flash
floods), steep slopes, scarce or no vegetation, or
vibrating or moving ground (e.g., from earthquakes or
industrial activities).
3. Mass Wasting
There are different forms of mass wasting:
Forms of mass wasting:
a. Debris Flow
happens when a large amount of sediments,
usually rocks of various sizes, falls down the
slope. Unlike a landslide, debris flow does not
need water to flow down.
b. Mudflow
happens when combined soil and water flow
down a slope. This usually happens near rivers
or streams where soil or sand is always moist or
has been soaked in water for a long time. This
weight of the mudflow indicates the severity of
risk when it flows down a community.
c. Slump
is a slow movement of
soil along a curved
surface. In time, the
area would look curved
because of depression
formed by the sinking
land.
4. Sedimentation
It is the accumulation of materials such as soil, rock
fragments, and soil particles settling on the ground. This
usually occurs in streams and sea erosion. Over time, the
sediment load becomes thick and forms a new layer of ground.
In some small inland waters, this sediment layer will
eventually dry up the water and become part of the soil. In
oceans, the sediment layer can form the ocean basin. Because
geologic processes are constant, ocean basins change in size
and depth. The change depends on the rate of erosion in their
surrounding continental masses or by ocean ridges.
ENDOGENOUS PROCESSES
The endogenous processes on Earth take place
within or in the interior of Earth. The driving
force is the thermal energy of the mantle.
Most of the thermal energy originates from
the decay and disintegration of radioactive
elements in Earth’s core.
The endogenous processes on Earth are responsible for
earthquakes, development of continents, mountain building,
volcanic activities, and other movements related to Earth’s
crust.
Earth's internal heat budget
is fundamental to the thermal history of the Earth. The flow
of heat from Earth's interior to the surface is estimated at
47±2 terawatts (TW)[1] and comes from two main sources in
roughly equal amounts: the radiogenic heat produced by the
radioactive decay of isotopes in the mantle and crust, and the
primordial heat left over from the formation of Earth.[2]
The Radioactive Decay
of elements in the Earth's mantle and crust results in
production of daughter isotopes and release of
geoneutrinos and heat energy, or radiogenic heat. Four
radioactive isotopes are responsible for the majority
of radiogenic heat because of their enrichment relative
to other radioactive isotopes: uranium-238 (238U),
uranium-235 (235U), thorium-232 (232Th), and
potassium-40 (40K).[14]
Primordial Heat
is the heat lost by the Earth as it continues to cool from its
original formation, and this is in contrast to its still activelyproduced radiogenic heat. The Earth core's heat flow—heat
leaving the core and flowing into the overlying mantle—is
thought to be due to primordial heat, and is estimated at 5–
15 TW. Estimates of mantle primordial heat loss range
between 7 and 15 TW, which is calculated as the remainder
of heat after removal of core heat flow and bulk-Earth
radiogenic heat production from the observed surface heat
flow.
Here are some of the endogenic processes that played a role in the
evolution of landforms on Earth:
1. Magmatism
Magma is the original materials that make up igneous
rocks. Originally found beneath the surface of Earth’s,
magma is very hot and is constantly moved by the internal
heat that reaches the mantle of Earth through
convective flow. Magmatism happens when magma is
generated and develops into igneous (magmatic) rocks.
The process can take place either under the surface or
on the surface of Earth.
2. Volcanism
(or plutonism). It is the process that usually happens
after magma is formed. Magma tries to escape from
the source through openings such as volcanoes or
existing cracks on the ground. Magma comes out with
extreme heat and pressure and may cause destructive
explosions. As soon as magma reaches the surface of
Earth, it is now called lava.
3. Metamorphism
It is the process of changing the materials that make up a
rock. The chemical components and geologic characteristics
of the rock changed due to heat and pressure that are
increasing or decreasing. The minerals in the rock may
change even if the rock does not melt. It should be noted
that rocks changing due to weathering and sedimentation
are not considered to have undergone metamorphism.
Metamorphism is the addition of heat and/or pressure to existing
rocks, which causes them to change physically and/or chemically so
that they become a new rock. Metamorphic rocks may change so
much that they may not resemble the original rock.
The two main types of metamorphism are both related to heat
within Earth:
Regional Metamorphism:
Changes in enormous quantities of rock over a wide area caused by
the extreme pressure from overlying rock or from compression
caused by geologic processes. Deep burial exposes the rock to
high temperatures.
Contact Metamorphism:
Changes in a rock that is in contact with magma because of the
magma’s extreme heat.
Formation of the different kinds of igneous rock
Intrusive (plutonic)
Igneous Rock
is formed when magma
cools and solidifies within
small pockets contained
within the planet’s crust.
The most common types of
plutonic igneous rock are
granite, gabbro, or diorite.
Formation of the different kinds of igneous rock
Extrusive (volcanic) Igneous Rock
Extrusive (volcanic) Rock
are so named because they are the result of magma
pouring onto the surface of the planet and cooling.
Extrusive igneous rocks include andesite, basalt,
obsidian, pumice, rhyolite, scoria, and tuff.
DEFORMATION OF THE EARTH'S CRUST
Learning Competencies:
Explain how the continents drift.
Cite evidence that support continental drift.
Explain how the movement of plates leads to the
formation of folds and faults.
Explain how the seafloor spreads.
Describe the structure and evolution of ocean basins.
The Continental Drift Theory
All these geologic processes continue to change appearance of
Earth.
1912, geophysicist Alfred Wegener (1880-1930) developed the
concept and hypothesized the continental drift theory.
He claimed that there used to be only one supergiant landmass
where all the continents came from. He called this massive
landmass Pangaea.
Over time, this continent broke apart into two huge landmasses
and these landmasses moved away from each other.
The two giant continents were Laurasia which comprised the
continents in the present-day Northern Hemisphere, and
Gondwanaland (also gondwana ) southern hemisphere.
Plate tectonics is the theory that Earth's outer shell is
divided into several plates that glide over the mantle, the
rocky inner layer above the core.
As early as 1929, Arthur Holmes (1890-965),
a British geologist, suggested the idea of
thermal convection as the driving force for
the movements of the continents. The
concept of thermal convection, as Holmes put
it, is based on the fact that as a substance is
heated, its density decreases and rises to
the surface until it is cooled and then sinks
again.
The repeating process of heating and cooling may produce a
current that is strong enough to make the continents move.
Holmes further suggested that thermal convection works like
a “conveyor belt” where the pressure that goes up could
break apart a continent. The broken pieces can be carried by
the same currents to opposite directions. In later years, the
concept of thermal convection was changed to mantle
convection currents to specify that heat is actually radiating
from the mantle.
While the basis for the movement of continents
progressed, geologists started to use a more precise term
to refer to the moving pieces as “plate” because it was
believed that continents are not the only ones moving (as
explained Wegener). The boundaries of tectonic plates
were accidentally discovered and eventually studied during
magnetic surveys of the ocean floor and seismic studies for
nuclear testing.
1. Divergent Boundaries
where plates move away from each other. Plates move apart
because of the magma that is being pushed upward in
boundaries of the plates. When this happens, the slowly
moving plates transport newly formed crust away from the
ridge as it spreads in both directions where the plates go.
2. Convergent ( collisional) Boundaries
where plates meet. This happens when two tectonic plates move
toward each other brought by mantle convection (or the current
convection from the heat of the mantle). Two possible landforms
can be created. One is a trench, which is formed from subduction
where a denser plate sinks (subducts) under the other (class
dense) plate. Another possible landform is a mountain or a
mountain range where neither plate is subducted but instead
crumples into each other and somehow pushed upward or
sideward. Convergent boundaries are where most of the
destruction of crust takes place, specifically in the subduction
zone.
3. Transform boundaries
where plates slide past each other. Neither plates gets
subducted.
Transform boundaries are places where plates slide sideways
past each other. At transform boundaries lithosphere is
neither created nor destroyed. Many transform boundaries
are found on the sea floor, where they connect segments of
diverging mid-ocean ridges. California's San Andreas fault is
a transform boundary.
Types of Stress That Influence Rock Behavior
The geologic processes that occur on Earth cause stress on rocks.
Geological stress is the force (from the pushing and pulling of
plates) that acts on the rocks thereby creating different behavior
or characteristics.
There are four different types of stress that influence rock behavior:
1.Tensional
In tensional stress, rocks are pulled apart. Rocks
may separate in opposite directions or move
farther away from one another.
Types of Stress That Influence Rock Behavior
2. Compressional
In compressional stress, rocks push or squeeze against one
another. The stress produced is directed toward the center.
Hence, when these rocks meet, the orientation could either
horizontal or vertical. Horizontally, the rush may thicken or
shorten. Vertically, the crust can thin out or break off.
Compressional stress is usually what takes place in folding,
which results in mountain building.
Types of Stress That Influence Rock Behavior
3. Shear
In shear stress, some of the portions of a plate at the edges
may break away in different directions, eventually making the
plate smaller in size. The friction caused by this stress can
cause earthquakes.
4. Confining
When stress is applied to all sides of the crust, confining
stress occurs.When this happens, the crust compacts, which
makes it look smaller. If the stress is too much for the crust
to handle, the crust can fracture from the inside.
FORMATION OF FOLDING & FAULTING
Folding
The buckling of a rock layer that was once
horizontal. Buckles or folds appear on the landscape.
The three major types of rock folding:
Monocline is a simple bend in the rock layers so that they are no
longer horizontal.
Anticlines are folded rocks that arch upward and dip away from the
center of the fold. The oldest rocks are at the center of an
anticline and the youngest are draped over them. When rocks arch
upward to form a circular structure, that structure is called a
dome.
Syncline is a fold that bends downward, causing the youngest rocks
to be at the center and the oldest are on the outside. When rocks
bend downward in a circular structure, that structure is called a
basin.
Faulting
Faulting is the result of the movement of the
earth plates. Faults occur where there is
stress along a weak point in the earth crust.
Three different types of faults: Normal, Reverse, and
Transcurrent (Strike-Slip).
Normal faults form when the hanging wall drops down. The
forces that create normal faults are pulling the sides apart,
or extensional.
Reverse faults form when the hanging wall moves up. The
forces creating reverse faults are compressional, pushing the
sides together.
Transcurrent or Strike-slip faults have walls that move
sideways, not up or down.
Normal faults
Transcurrent or Strike-slip
faults
SEAFLOOR SPREADING
is a continuous process when tensional forces on both sides
of the plates cause them to constantly move apart. Magma
rises to the surface from the mantle. In time, the magma is
cooled by seawater and forms the oceanic crust.
Seafloor spreading is a process that occurs at mid-ocean
ridges, where new oceanic crust is formed through volcanic
activity and then gradually moves away from the ridge
HISTORY OF EARTH
Relative Dating
Relative dating is a method used to determine the relative
order of geologic events. This is done through stratigraphy
(succession of rocks) where the order of rock formations
correlates to geologic time. The topmost layer suggests the
most recent. In like manner, the oldest rocks are understood
to be at the bottom. This method does not provide actual
numerical dates for the rocks, but all are just estimates based
on the profile of the strata which includes chemical
composition, rock type, and presence of organisms.
Absolute Dating
Absolute dating methods can tell which sediments were deposited first and
also the approximate age of the specimen. The most used and accepted form
of absolute dating is radioactive decay dating.
Most absolute dating makes use of radiometric methods, wherein radioactive
minerals are used to compute the age of rocks. Isotopes, which are present
in radioactive elements, break down at a constant rate. These rates of decay
are known, so if you are able to measure the parent and daughter isotopes in
rocks, you can calculate when the rocks were formed.Since different
elements have unique decay rates, certain elements are used for dating a
particular age range.
QUESTIONS?