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151PTE321 / GEOL2101 Engineering Geology

Lecture 1

Dr. Seyed Mehdi Seyed Alizadeh

Composition of the earth, Plate Tectonic, and Geologic Time

Introduction

Geology is a complex, integrated system of related parts, components, or sub- systems that interact in an organized fashion, affecting one another in various ways.

The interaction of these subsystems has resulted in a dynamically changing planet in which matter and energy are continuously recycled into different forms.

Introduction

• Geology is the study of the Earth.

• Physical geology is concerned with the materials and processes which compose and operate on the surface of, and within, Earth.

• Historical geology is concerned with the origin and evolution of Earth's continents, oceans, atmosphere, and life.

What is geology?

What is geology?

Geologists are employed in diverse occupations.

• Principal occupations include:

• Mineral and energy resource exploration

• Solving environmental problems

• Predicting natural disasters

Geology and the Formulation of Theories

• What is a theory? • It is arrived at through the scientific method, which

involves

• gathering and analyzing facts

• formulating hypotheses to explain the phenomenon

• testing the hypotheses

• and finally proposing a theory.

• The hypotheses is a tentative explanation.

• A scientific theory is a testable explanation for some natural phenomenon, that is supported by a large body of evidence.

How Does Geology Relate to the Human Experience?

• Geology pervades our everyday lives and is a part of many aspects of human experience, including the arts and literature.

• The range of environmental problems and issues of concern to society require a basic understanding of geology.

Global Geologic and Environmental Issues Facing Humankind

• Most scientists would argue that overpopulation is the greatest problem facing the world today.

• Increasingly large numbers of people must be fed, housed, and clothed, with a minimal impact on the environment.

Global Geologic and Environmental Issues Facing Humankind

• The greenhouse effect is the retention of heat in the atmosphere, which results in an increase in the temperature of Earth’s surface and atmosphere, thus producing global warming.

Our Solar System

• Its Origin and Evolution

• The Solar System formed from a rotating cloud of interstellar matter about 4.6 billion years ago.

• This cloud, upon condensing, collapsed under the influence of gravity and flattened into a rotating disk.

• The sun, planets, and moons formed within this disk.

Subsystems of earth

• The principal subsystems

of the earth are the:

• Atmosphere

• Biosphere

• Hydrosphere

• Lithosphere

• Mantle

• Core

Earth

• Its Place in Our Solar System

• Earth formed from a swirling eddy of nebular material 4.6 billion years ago, accreting as a solid body and soon thereafter differentiated into a layered planet during a period of internal heating.

Chemical:

1) Core: Ni and Fe

2) Mantle: Mostly Peridotite

3) Crust: Many different kinds of rocks (for the most part, continents composed of granite and ocean basins composed of basalt)

Mechanical:

1) Inner Core: Solid

2) Outer Core: Liquid and convective—source of earth’s magnetic field

3) Mesosphere (lower mantle): Solid

4) Asthenosphere: Ductile and weak

5) Lithosphere: Brittle and strong, uppermost layer of crust

The seismic evidence shows that the earth's internal structure is in the form of shells of

different composition, with density increasing with depth as also the velocities of different

types of waves .

The earth composes of two elements as following:

What is Earth Made of?

Why Earth is a Dynamic and Evolving Planet

• Earth has continuously changed during its 4.6 billion year existence as a result of interactions between its various subsystems and cycles.

• Earth is composed of 3 concentric layers.

• Core • Mantle • Crust

Components of Earth

The outermost layer, the crust, is divided into:

• thick continental crust

• thin oceanic crust

Components of Earth - crust

 Crust is made up of several elements: oxygen, 47 percent; silicon, 27 percent; aluminum, 8 percent; iron, 5 percent; calcium, 4 percent; magnesium, potassium and sodium, 2 percent

The mantle surrounds the core and is divided into:

• a solid lower mantle

• an asthenosphere that behaves plastically and flows slowly

• a solid upper mantle composed primarily of peridotite, an igneous rock made of olivine.

Components of Earth - mantle Mantle: under the crust is about 1,800 miles deep (2,890 km). It is composed mostly of silicate rocks rich in magnesium and iron. Intense heat causes the rocks to rise. They then cool and sink back down to the core. This convection — like a lava lamp — is believed to be what causes the tectonic plates to move. When the mantle pushes through the crust, volcanoes erupt.

The core consists of

• a small, solid inner region

• a larger, liquid, outer portion

Components of Earth - core

Core: At the center of the Earth is the core, which has two parts. The solid, inner core of iron has a radius of about 760 miles (about 1,220 km). It is surrounded by a liquid, outer core composed of a nickel-iron alloy.

• The Asthenosphere:

• Surrounds the lower mantle

• Behaves plastically and slowly flows

• Partial melting in the asthenosphere generates magma (molten rock) that rises to the earth’s surface.

Components of Earth - asthenosphere

• The Lithosphere

• The crust and upper mantle make up the lithosphere which forms the solid outer layers of the Earth.

Components of Earth - lithosphere

Boundary between crust and mantle

1. Mohorovicic Discontinuity

2. Gutenberg Discontinuity

4. Tectonic plates

• The Mohorovičić discontinuity : usually referred to as the Moho, is the boundary between the Earth's crust and the mantle.

• The Gutenberg discontinuity: occurs within Earth's interior at a depth of about 2,900 km (1,800 mi) below the surface, where there is an abrupt change in the seismic waves (generated by earthquakes or explosions) that travel through Earth.

Plate Tectonics

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. The plates act like a hard and rigid shell compared to Earth's mantle. This strong outer layer is called the lithosphere.

The crust is divided into “plates”

• Convection in the mantle moves these “plates” relative to one another

• Overarching theory to explain mountain ranges, basins, and movement of continents

Plate Tectonic Theory

• The lithosphere is composed of rigid plates that diverge, converge, or slide sideways past one another as they move over the asthenosphere

The zones of contact between “plates” are known as boundaries; boundaries can be either continental or oceanic depending on geographic location and do not necessarily define the earth’s continents.

Plate Tectonic Theory - boundaries

Plate Tectonic Theory

• Volcanoes and earthquakes occur at the boundaries between the plates.

• Plate tectonic theory is a unifying explanation for many geologic features and events, helping us understand the composition and internal processes of Earth on a global scale.

Plate Tectonic Theory

Plate tectonics & earth

• The earth has been calculated to be 4.6 billion years old

• Plate tectonics has been changing the “face” of the earth as it moves the continents together and apart again drastically changing the climate and biota

The Earth Plate Tectonic Movements

Types of plate boundaries

1. Transform boundaries (Conservative) : occur where two lithospheric plates slide, or perhaps

more accurately, grind past each other along transform faults, .

The relative motion of the two plates is either sinistral (left side toward the observer) or dextral

(right side toward the observer). Transform faults occur across a spreading center. Strong

earthquakes can occur along a fault. The San Andreas Fault in California is an example of a

transform boundary exhibiting dextral motion

2. Divergent boundaries (Constructive) :occur where two plates slide apart from each other. At

zones of ocean-to-ocean rifting, divergent boundaries form by seafloor spreading, allowing for

the formation of new ocean basin. As the continent splits, the ridge forms at the spreading

center, the ocean basin expands, and finally, the plate area increases causing many small

volcanoes and/or shallow earthquakes.

3. Convergent boundaries (Destructive) (or active margins): occur where two plates slide

toward each other to form either a subduction zone (one plate moving underneath the other)

or a continental collision. At zones of ocean-to-continent subduction (e.g. the Andes mountain

range in South America, and the Cascade Mountains in Western United States), the dense

oceanic lithosphere plunges beneath the less dense continent.

Types of plate boundaries

Example:Divergent boundaries

More Examples of Plate Boundaries

Examples:Transform boundaries

Evidence for Plate Movement

• Pattern of magnetic “stripes” in ocean rock (basalt) on ocean floor that reflect earth’s magnetic reversals;

• Nasa Satellite GPS tracking movement of plates;

• Plates move at average speed of 3cm per year (3 cm/yr)

Geologic Time • An appreciation of the immensity of geologic time is central

to understanding the evolution of the Earth and its’ life.

• Geologic time differs from the human perspective of time

• Earth goes through cycles of much longer duration than the human perspective of time

• The immense span of time encompassed by the Earth's existence and geological processes sets geology apart

• The geologic time scale is the calendar that geologists use to date past events in Earth’s history.

Geologic Time and Uniformitarianism

• Uniformitarianism forms a cornerstone of geology. It is a fundamental principle of geology.

• This principle states that the laws of nature have remained unchanged through time and thus, that the processes observed today have also operated in the past, though possibly at different rates.

• Therefore, to understand and interpret geologic events from evidence preserved in rocks, geologists must first understand present-day processes in rocks.

How does the study of geology benefit us?

• Understanding how the Earth’s subsystems work will help ensure the survival of the human species.

• It will help us to understand how our actions affect the delicate balance between these systems.

Geologic Time

The geological time scale (GTS): is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, and other Earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history

Glossary Eon: The longest geologic time unit: Phanerozoic Eon includes Paleozoic, Mesozoic and Cenozoic eras.

Epoch: A geologic time unit longer than an age and shorter than a period.

Era: A geologic time unit smaller than an eon.

Example: We are currently living in Eon: Phanerozoic, Era: Cenozoic, Period: quaternary and Epoch: Holocene

Precambrian

Phanerozoic (Paleozoic + Mesozoic)

Phanerozoic (Cenozoic)

How old is Petroleum?

- So how old is Petroleum? Petroleum has been found in formations of widely different ages (millions of years) reflecting different depositional environments at different times for the same location.

- Available evidence indicates that rocks of certain geologic ages are much richer in petroleum than those of other ages.

- Precambrian, Cambrian, and Triassic rocks have each produced less than 1% of the world’s oil.

- Pleistocene rocks have produced none.

- Tertiary rocks have produced 58% of the world’s oil.

- Cretaceous rocks have produced 18%.

- Paleozoic rocks have produced 15% of the world’s oil.

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