Essentials of Geology, 10e

An Introduction to GeologyChapter 1

The science of geologyGeology is the science that pursues an understanding of planet Earth

• Physical geology – examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface

• Historical geology – seeks an understanding of the origin of Earth and its development through time

The science of geologyGeology, people, and the environment

• There are many important relationships between people and the natural environment

• Some of the problems and issues addressed by geology involve natural hazards, resources, world population growth, and environmental issues

The science of geologySome historical notes about geology

• The nature of Earth has been a focus of study for centuries

• Catastrophism• Uniformitarianism and the birth of

modern geology

Geologic timeGeologists are now able to assign fairly accurate dates to events in Earth historyRelative dating and the geologic time scale

• Relative dating means that dates are placed in their proper sequence or order without knowing their age in years

Geologic timeThe magnitude of geologic time

• Involves vast times – millions or billions of years

• An appreciation for the magnitude of geologic time is important because many processes are very gradual

The geologic time scale

Figure 1.9

The nature of scientific inquiryScience assumes the natural world is consistent and predictableThe goal of science is to discover patterns in nature and use the knowledge to make predictionsScientists collect facts through observation and measurements

The nature of scientific inquiryHow or why things happen are explained using a

• Hypothesis – a tentative (or untested) explanation

• Theory – a well-tested and widely accepted view that the scientific community agrees best explains certain observable facts

The nature of scientific inquiryScientific method

• Scientific method involves gathering facts through observations and formulation of hypotheses and theories

There is no fixed path that scientists follow that leads to scientific knowledge

Earth as a systemEarth is a dynamic planet with many interacting parts or spheresParts of the Earth system are linked It is characterized by processes that

• Vary on spatial scales from fractions of a millimeter to thousands of kilometers

• Have time scales that range from milliseconds to billions of years

The intersection of three spheres The atmosphere, hydrosphere, and the geosphere

Figure 1.14

Earth as a systemThe Earth system is powered by the Sun, which drives external processes

• In the atmosphere• In the hydrosphere• At Earth’s surface

Earth as a systemThe Earth system is also powered from Earth’s interior

• Heat remaining from the Earth’s formation and heat that is continuously generated by radioactive decay powers the internal processes that produce volcanoes, earthquakes, and mountains

Formation of Earth

• The solar system evolved from an enormous rotating cloud called the solar nebula.

Most researchers conclude that Earth and the other planets formed at essentially the same time.Nebular Hypothesis

Formation of Earth

Formation of Earth

• The nebula was composed mostly of hydrogen and helium.

Nebular Hypothesis

• About 5 billion years ago, the nebula began to contract.

• It assumed a flat, disk shape with the protosun (pre-Sun) at the center.

Formation of Earth

Formation of Earth

• Inner planets begin to form from metallic and rocky clumps.

Nebular Hypothesis

• Larger outer planets began forming from fragments with a high percentage of ices.

Formation of Earth

Nebular hypothesis

• Emanuel Swedenborg -(1734)• a Swedish scientist and philosopher

The Nebular Hypothesis

A

C

D

E

B

Origin of Solar System

Our Solar System

Evolution of the Earth

Artist’s View of Comets hitting the Planet

Comets: Artists view

Layered Structure of The Earth

Melting of the original materials occurred due to heat generated by.

Impact of falling meteoritesCompression of rocks due to gravityDecay of radioactive elements

Heavy metals (e.g. iron & nickel) sank deeper whereas lighter elements (e.g. oxygen & silicon) accumulated in the outer parts .This process is known as differentiation (fractionation) which led to the formation of a layered structure.

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Planetesimalsstrike growingEarth

Iron melts andbegins to sink

Lighter materialsconcentratecloser to surface

Crust andmantle

Inner core

AtmosphereCrust

MantleOuter core

Liquidcore The moon formed

after a Mars-sized planet hit earth, about 4.6 byaWe use that event as Earth’s origin date

DIFFERENTIATION

Interior of Earth is hotter than surface

Process of differentiation

While it was still in the molten state, separation of elements occurred within the earth. Light Inert Gases like Helium (He) and Krypton (Kr) were lost to outer space Heavy elements like Nickel (Ni) and Iron (Fe) sink to the center.

Earth’s Internal Structure

Earth’s internal layers defined by Chemical compositionPhysical propertiesDeduced from Seismographs of EarthquakesMeteorites lend support

Layers defined by compositionCrustMantleCore

Iron-Nickel Meteorite

Formation of Earth Layers Form on Earth

Formation of Earth

• As Earth formed, the decay of radioactive elements and heat from high-velocity impacts caused the temperature to increase.

• Lighter rocky components floated outward, toward the surface.

• Gaseous material escaped from Earth’s interior to produce the primitive atmosphere.

Earth's Major Spheres1. Hydrosphere

• Ocean is the most prominent feature of the hydrosphere. - Is nearly 71% of Earth's surface- Holds about 97% of Earth's water

• Also includes fresh water found in streams, lakes, and glaciers, as well as that found underground

Earth's Major Spheres

Earth's Major Spheres 2. Atmosphere

• Thin, tenuous blanket of air • One half lies below 5.6 kilometers (3.5 miles)

3. Biosphere• Includes all life • Concentrated near the surface in a zone that

extends from the ocean floor upward for several kilometers into the atmosphere

Earth's Major Spheres

Earth's Major Spheres

Earth's Major Spheres

4. Geosphere• Based on compositional differences, it

consists of the crust, mantle, and core.- Crust—the thin, rocky outer layer of Earth.- Mantle—the 2890-kilometer-thick layer of

Earth located below the crust.- Core—the innermost layer of Earth, located

beneath the mantle.

End of Chapter 1