What is Geology?
• The first known geological map was created by ancient Egyptians over 3000 years ago.
• The scientific discipline of geology as we understand it today came into being only in the late
• The industrial revolution in northern Europe caused a growing demand for energy and minerals
(ie. Coal, limestone, iron and water) Finding and exploiting these resources forced new ways of
investigating plant earth, this is the job of geologist.
• One of the earliest geology maps was published in England in 1815 by William Smith, he is
known as the “father of english geology”
• In North America, geological mapping began in the mid 19 century and was also driven by the
need to locate resources for an ever expanding population.
• Sir William Logan was the founding director of the Geological Survey of Canada (1842) and
was the first to systematically describe the geology of Canada
• In the late 17 century it was widely believed that the Earth was only 6000 years old, and had
essentially remained the same. However now it is determined that the earth is over 4500 million
years old and in that time the life forms, as well as the physical geography have changed
dramatically.The ever changing nature of physical environments on planet earth, along with the
role of extra-terrestrial processes are seen as having largely controlled the evolution of life
• The movement of earths continents was suggested in the early 20 century by Alfred Wegener.
In 1912 Wegener coined the concept of continental drift, which is a concept that the continents
were once one large land mass called Pangea and over time had moved apart from each other.
• Though Wegener collected a wealth of evidence to support his idea of continental movement,
however he couldn't convincingly prove how it happened, therefore people rejected his theory. It
took years of gathering geo-physical and geological data from oceans and the margins of
continents for geoscientists to prove Wegener's theory. This is turn lead to the development of
the plate tectonics theory.
• It was Canadian geologist J.Tuzo Wilson who in the early 1970's was responsible for bringing
together several of the key elements of what we now know as plate tectonics.
Time and Geology
• Geology involves vastly greater amounts of time, often referred to as deep time
• Some geological processes occur quickly, such as a great landslide or a volcanic eruption. These
events occur when stored energy is suddenly released. Most geological processes are slow but
relentless reflecting the pace at which the Earth's processes work.
• “rapidly” to a geologist may mean that within a few million years a hill will be reduced nearly to
• The rate of plate motion is relatively fast, if new magma erupts and solidifies along a mid
oceanic ridge we can easily calculate how long it will take the igneous rock to move 1000
kilometres away from the crest of the ridge. At the rate of 1 cm per year, it will take 100 million
years for the currently forming part of the crust to travel 1000 kilometres.
• The earth is estimated to be at least 4.55 billion years old
What do Geoscientists do?
• Traditional geologists spent most of their time in the field looking for signs of minerals.
www.notesolution.com Exploration geologists were formerly called prospectors performed this job.
• Geoscientists may work for an exploration company looking for gold silver and other medals-
or more recently for diamonds.
• The discipline of geology has broadened its scope over the past several decades. The location of
geological resources are more important than ever, however at the same time the skills of the
geoscientists are required to address additional issues such as migration of the effects of natural
hazards and other environmental concerns.
• Modern geologists specialize in a number of areas:
Geochemists are comfortable working in the ordered environment of the laboratory and use
high technology equipment to analyze the chemistry of rocks or minerals.
Mineralogists study minerals.
Petrologists study the make up of rocks and how they form.
Other geoscientists called geophysicists employ high tech equipment in the field (ie boats,
ships, planes, or satellites.) to learn more about the physical conditions on or under the
Petroleum geologists search for oil and gas.
Seismologists study how to measure and mitigate earthquake activity.
Paleontologist is a specialist who studies the fossilized remains of ancient organisms, wether
gigantic dinosaurs or the remains or organisms to small to see without a powerful
microscope (micro paleontologist)
Glacial geologists study the landforms and sediments left behind from when the ice sheets
covered the northern part of North America in Canada
Hydrogeologists study and protect the water within sediments because it is an increasingly
• Todays geoscientists have the advantage of working in many different areas, both by geography
and topic. Some include teaching, and working for the government.
• APGO- The association of professional geologists
• APEGGA- The association of Professional Engineers, Geologists, and Geophysicists of Alberta
• Geoscientists often deal with information that is sensitive and/or financially significant (e.g a
parcel of land that has been extensively contaminated by chemicals, or mineral deposits that
haven been discovered.)
Environmental Geology: New Challenges for Geoscientists
• Basic commodities such as metals, oil and gas still need to be found and exploited.
• Canada is now one of the most urbanized countries in the world, with more than 75% of its
population living in cities and towns. Urban populations create large amounts of waste, consume
cast quantities of water, and create many environmental problems.
• The new challenge for today's geoscientist is to relate to the finding and managing of drinking
water, and in dealing with a wide variety of wastes ranging from radioactive waste to household
• Environmental problems are dealt with by environmental geoscientists, they help determine
where sufficient groundwater is, and how it can be protected.
• Questions such as “have past land uses released contaminants into the ground- and if so, where
are they?” need to be answered. In order to do this, environmental geoscientists increasingly
need to “see” underground using geophysical techniques, geochemical data, and flow models to
create a 3-d picture of what is below our feet. The 3-D arrangement of strata and the type of
www.notesolution.com strata themselves, control the movement of groundwaters (and also contaminants) These are key
considerations in finding clean drinking water, determining safe locations for storing wastes,
and identifying the environmental impact of past waste-disposal activity.
• Creation of digital maps, and 3-d geological models for resource exploration and environmental
and engineering applications is one of the roles of a geomatician. Geomaticians collect,
organize, analyze, and create images from any spatial and geographic data available in digital
• Geoscientists usually work as part of a team with biologists, lawyers, engineers, planners and
policy makers. They commonly work for an environmental consulting company or increasingly,
municipal of provincial government.
• Modern society needs geoscientists because they appreciate and understand geological
processes and they are aware of all the different years of Earth's history.
• Geoscientists are used to thinking in 3D and far back in time, using a wide range of geological,
physical, and chemical data- along with their imagination- to reconstruct the distribution of
subsurface layers to show how an area has evolved through geologic time.
What is the Scientific Method?
• Problem/Question-What is the problem or question?
• Methodology/Data collection
How did the Earth Form?
• The earth is very old and and is unique within the solar system in having not only a solid body,
but also oceans, an atmosphere and life. These individual components continuously interact to
form the complex and dynamic system we refer to as the Earth system.
• The universe was formed by the clumping together of gas and debris in the aftermath of the big
bang that is thought to have occurred 15 billion years ago.
• There are billions of galaxies in the universe, the Milky way contains our own solar system and
• The solar system was created from a cloud of gas and dust particles called a nebula. This cloud
of gas and dust began to rotate and contract, creating bulbous core surrounded by a flattened
disc. The core progressively collapsed to the point where nuclear fusion began, and our sun was
formed sometime fewer than 5 billion years ago.
• Dust in the outer disc condensed to form rocks and metals that combined to form large rounded
planets and much smaller, irregularly shaped Planetesimals.
• The process of building large bodies of matter through collisions and gravitational attraction is
• Terrestrial planets are small dense and rocky they include Mercury, Venus, Earth and Mars.
• Jovian Planets have low densities and include Jupiter, Saturn, Uranus, and Neptune.
What was the Early Earth like?
• Soon after the Earth was formed, it collided with a planetismal- the Earth's moon was created
from the debris that flung off into space.
• In its final stages of formation, about 3.9 billion years ago the earth swept up chunks of space
www.notesolution.com debris and in the process was bombarded by huge meteorites. Few impact craters produced by
these ancient meteorite collisions can be identified on the earth's surface today, as they have
either been buried by subsequent deposits of removed by tectonic movements or erosions.
• More geologically recent impact craters can be recognized and provide evidence of a violent
• Differentiation- the process zonation of heavier metals like iron and nickle that settle towards
the planet's centre, and lighter materials such as silica and oxygen rise towards the earths
surface, under certain conditions.
Internal Structure of the Earth
• Earth is said to be differentiated because intense heat and pressure within the body of the planet
gives rise to “onion life” layers of different chemical composition and physical behaviour.
• Evidence suggests that layers form an innermost core, composed of iron allow, a mantle
composed of Fe-Mg silicates (forming a rock called peridotite), and an outer most crust
composed of lighter rocks such as basalt and granite.
• Lithospheric plates- mantle convection breaks the crust and uppermost ridge mantle into large
• Weak pieces are pushed around the surface of the planet over a weak layer called the
• Movement of rigid lithospheric plates over the more mobile asthenosphere is the fundamental
process involved in plate tectonics.
• Outgassing- a process in which volcanic eruptions release gaseous elements and created earth's
Convergent Boundaries and Ore Deposits
• Silvers of ancient oceanic crust exposed on land may contain these rich ore minerals in
relatively intact form.
• Volcanism at island arcs can also produce hot-spring deposits on the flanks of the andesitic
volcanos. Pods of rich ore collect above local bodies of magma, and the ore is sometimes
distributed as sedimentary layers in shallow basins.
• Circulation pattern and the ore forming processes are similar to those of spreading centres,
however island arc ores usually contain more lead and gold.
• Subduction of the sea floor beneath a continent produces broad belts of metallic ore deposits
near the edge of the continent. The origin of the continental ores above a subduction zone is not
clear. Hot spring deposits from the ridge crest are subducted with oceanic crust and could
become remobilized to rise into the continent above.
How do Mountain Ranges Form?
Orogenies and Plate Convergence:
• An orogeny is an episode of mountain building, often characterized by intense deformation of
the rocks in a region.
• Mountain belts form along plate margins, particularly where plate convergence compresses the
crust causing uplift and deformation. Knowing this information allows us to better understand
past mountain building processes.
• Ocean-continent convergence:
an accretionary wedge develops where newly formed layers of marine sediment are folded
and faulted as they are snowploughed off the subducting oceanic plate.
www.notesolution.com If rocks are carried far enough down in the subduction zone it becomes metamorphosed.
Fold and thrust belts may develop on the craton side of the mountain. Thrusting is away
from the magmatic arc toward the craton. The magmatic arc is at a high elevation, because
the crust is thicker and composed largely of got igneous and metamorphic rocks.
The thrusting is largely due to the crustal shortening caused by convergence.
• Arc-Continent Convergence:
When an island arc and a continent collide the intervening ocean is destroyed by subduction.
When collision occurs, the arc, like a continent is to buoyant to be subducted. Continued
convergence of the two plates may cause the remaining sea floor to break away from the arc
and create a new site of subduction and a new trench seaward of the arc.
The new subduction faces the opposite direction of the original subduction. (sometimes
called a flipping subduction zone.)
• Continent-Continent Convergence
Some mountain belts form when an ocean basin closes and continents collide. Mountain
belts that we find within continents are hypothesized to be products of continent-continent
The Himalayan orogeny started around 45 million years ago as India began to colliding with
The process of continental splitting and collision was responsible for adding the Maritime
provinces onto the Canadian Shield. Early in the Mesozoic Pangea split roughly parallel to
the old suture zone, and the continents of North America, Africa, and Europe separated as
the modern Atlantic Ocean began to form.
The cycle of splitting of a supercontinent, opening of an ocean basin, closing of the basin,
and collision of continents is known as the Wilson Cycle. Canadian geophysicists J. Tuzo
Wilson proposed the cycle in the 1960's.
How Do Plates Change Over Time?
• Not only do plates move, boundaries do as well. Plate move away from each other at a divergent
boundary on a ridge crest for tens of millions of years, but the ridge crest can be migrating
across Earth's surface as this occurs. Ridge crests can also jump into new positions.
• Convergent boundaries migrate too. Trenches and magmatic arcs migrate along with the
boundaries. Convergent boundaries can also jump, subduction can stop in one place and begin
in a new place.
• Transform boundaries also change position.
• Geodetic studies have shown that nearly 25% of plate motion between the North American and
Pacific plates is accommodated along faults in eastern California and western Nevada.
• Plates can change in size
What Causes Plate Motions
• There are many speculations as to why plates move:
Mid-Oceanic ridge crests are hot and elevated, while trenches are cold and deep
ridge crests have tensional cracks
the edges of some plates are subducting sea floor, while the edges of other plates are
continents )which can not subduct.
• Convection in the mantle, proposed as a mechanism for sea-floor spreading, can account for
www.notesolution.com these facts.
• Mantle convection is quite likely because heat loss from the Earth's core should heat the
overlaying mantle, causing it to overturn.
• Cold lithospheric plates may be subduct down to the core-mantle boundary, whereas other less
dense plates may only reach 670-km boundary. One of the most recent models suggest that the
lowermost part of the mantle does not mix with the upper and middle mantle. And acts as a
“lava lamp” turned on low, fuelled by internal heating and heat flow across the core mantle
• The basic question in plate motion is why do plates diverge and sink? 2 or 3 different
mechanisms may be at work:
Ridge-push- as the plates move away from a divergent boundary, it cools and thickens.
Cooling sea floor subsides as it movies, and this subsidence forms the board side slopes of
the mid-Oceanic ridge. A slope also forms between the lithosphere and the asthenosphere,
which may have a relief of 80-100 km.
Slab Pull- Cold lithosphere sinking at a steep angle through hot mantle should pull the
surface part of the plate away from the ridge crest and then down into mantle as it cools.
Slab pull is though to be at least twice as important as ridge push in moving an oceanic plate
away from a ridge crest. Slab pull is hypothesized to cause rapid plate motion.
Trench-suction- when subducting plates fall into the mantle at angles steeper than their dip,
then trenches and the overlying plates are pulled horizontally seaward toward the subducting
• All three mechanisms especially in combination are compatible with high, hot ridges; cold deep
trenches; and tensional cracks at the ridge crest. They can account for the motion of both
oceanic and continental plates.
• The reasons for plate motions are the properties of the plates themselves and the pull of gravity.
This idea is in sharp contrast to most convection models, which assume that plates are dragged
along by the movement of mantle rock beneath the plates.
How are Mantle Plumes and Hot Spots Related?
• Mantle plums are narrow column