Intro Geology

An Introduction to Geology

The Science of Geology

Geology - 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 Geology

Geology, people, and the environment • Many important relationships exist

between people and the natural environment

• Problems and issues addressed by geology include

• Natural hazards, resources, world population growth, and environmental issues

Geologic time

Geologists are now able to assign fairly accurate dates to events in Earth history (absolute dating)

Relative 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

Thegeologic

timescaleFigure 1.7

PrecambrianPrecambrian•4.6 billion years to 544 million years.•Represents 88% of all of the history of the earth.•Referred to as the Cryptozoic Eon.

–“hidden life”

(prokaryotes)

(no more BIFs)

88% of geologic time

Precambrian: The First 4 Billion Years

Geologic time

The 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 (uniformitarianism)

• Earth 4.6 Billion Years Old

The nature of scientific inquiry

Science assumes the natural world is consistent and predictable

Goal of science is to discover patterns in nature and use the knowledge to make predictions

Scientists collect data through observation and measurements


How or why things happen is 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

• Law-a general observation that holds true without explaining why it holds true


Scientific method involves• Gathering facts through observations (data)• Formulation of hypotheses and theories

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

A view of Earth

Earth is a planet that is small and self-contained

Earth’s four spheres • Hydrosphere• Atmosphere• Biosphere• Solid Earth

Earth’sSpheres

Atmosphere

LITHOSPHERE Land Contains all the cold, hard, solid land of Earth’s crust (surface), the semi-solid land underneath the crust, and the liquid land near the center.

ATMOSPHERE AirContains all the air in Earth’s system.

BIOSPHERE Living ThingsContains all of Earth’s living things—microorganisms, plants, and animals.

HYDROSPHERE WaterContains all the solid, liquid, andgaseous water of Earth.

What is the Biosphere? All regions of the Earth that are

capable of supporting life. Evolved about 3.5 billion years ago 20-30 km thickness (deep ocean

trenches into the atmosphere) Includes portions of the hydrosphere,

lithosphere, atmosphere, and cryosphere.

The global ecosystem is called the biosphere It is the sum

of all the Earth's ecosystems

The biosphere is the most complex level in ecology

The biosphere is the total of all of Earth's ecosystems

THE BIOSPHERE

Figure 34.2A

The BiosphereThe Biosphere

We divide the total biosphere into three parts

• the Atmosphere

• the Hydrosphere

• the Lithosphere


It is the physical and chemical parameters of each habitat that selects for the autochthonous community.


The Biosphere (a.k.a. Ecosphere) - the totality of life on earth and the abiotic surroundings that is inhabited.

Earth minus sterile areas: strata below the crust upper atmosphere habitats of extreme heat or lacking liquid

water

Hydrosphere The earth’s water is found as a

LIQUID in rivers, lakes, oceans, rain GAS in our atmosphere SOLID in snow and ice

71% of the earth’s surface is covered by water

Processes of the Hydrologic Cycle

Evaporation - the transformation of water from a solid or liquid to a gaseous state

Condensation - transformation of vapor into a liquid

Precipitation - liquid or solid water that falls from the atmosphere to the earth’s surface

The HydrosphereThe Hydrosphere

Freshwater

Limnetic Habitats (Limnology)

2. Lotic Habitats (running water)a. Springsb. Streamsc. Rivers

The HydrosphereThe Hydrosphere Freshwater - Lake Zonation

surface

littoral zone

limnetic zone (P>R)

profundal zone (P>R)

compensation depth

euphotic zone

OceansOceans

0.5% Groundwater 0.02% Rivers and Lakes

Structure of Atmosphere

From Cunningham & Cunningham, 2004, Fig. 9.1

Atmospheric Composition % by VolumeMajor Constituents

Nitrogen 78.1Oxygen 20.9

Active Minor ConstituentsWater vapor (H2O) variable (0.48 aver.)Carbon Dioxide (CO2) 0.035Methane (CH4) 0.00014Nitrous oxide (NO2) 0.00005Ozone (O3) 0.000007CFC’s 0.00000014H2O (liq & ice) 0.00000002

Inactive Minor ConstituentsArgon 0.93Neon 0.0018Helium 0.00052Krypton 0.0001Xenon 0.000009

Other Components of the Atmosphere Water Droplets Ice Crystals Sulfuric Acid Aerosols Volcanic Ash Windblown Dust Sea Salt Human Pollutants

Structure of the Atmosphere Defined by Temperature Profiles Troposphere

Where Weather Happens Stratosphere

Ozone Layer Mesosphere Thermosphere

Ionosphere

Troposphere This is the layer

that is closest to the surface of the earth

It’s elevation ranges from 0 to 10 km

Stratosphere This layer sits on top

of the troposphere It’s elevation ranges

from 10 km to around 25 km

This layer contains the ozone layer, which protects us from harmful sunlight

Mesosphere This layer is above

the stratosphere It’s elevation

ranges from 25 to 100 km

http://www.njcmr.org/distils/lab/ozone/layer.jpg

Thermosphere This is the highest layer

of the atmosphere It’s height ranges from

100 to 400 km This is where most

small meteorites burn up and is also the location in the atmosphere that the northern lights occur (aurora borealis)

Why is the Mesosphere so Cold? Stratosphere warmed because of

ozone layer Thermosphere warmed by atoms

being accelerated by sunlight Mesosphere is sandwiched between

two warmer layers

Composition and Altitude Up to about 80 km, atmospheric

composition is uniform (troposphere, stratosphere, mesosphere)

This zone is called the homosphere Above 80 km light atoms rise This zone is sometimes called the

heterosphere

Atmosphere

The surrounding air of the Earth

Earth as a system

Earth is a dynamic planet with many interacting parts or spheres

Earth System Science• Aims to study Earth as a system composed

of numerous interacting parts or subsystems• Employs an interdisciplinary approach to

solve global environmental problems

Earth as a system

The Earth system is powered by the Sun that drives external processes in the

• Atmosphere• Hydrosphere• At Earth’s surface

The Earth system is also powered by Earth’s interior

Earth as a system

What is a system • Any size group of interacting parts that

form a complex whole• Open vs. closed systems

Feedback mechanisms• Negative feedback – maintains the status

quo• Positive feedback – enhances or drives

changes

Early evolution of Earth

Origin of planet Earth • Most researchers believe that Earth and the

other planets formed at essentially the same time

• Nebular hypothesis • Rotating cloud called the solar nebula• Composed of hydrogen and helium • Nebula began to contract about 5 billion years

ago


Origin of planet Earth • Nebular hypothesis

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

• Inner planets begin to form from metallic and rocky substances

• Larger outer planets began forming from fragments of ices (H2O, CO2, and others)

The Nebular Hypothesis


Formation of Earth’s layered structure • Metals sank to the center• Molten rock rose to produce a primitive

crust• Chemical segregation established the three

basic divisions of Earth’s interior • Primitive atmosphere evolved from gases in

Earth’s interior

How did Earth become density stratified?

Young Earth was probably homogeneous Heat and gravitational pressure caused Earth to partially

melt Gravity then pulled the iron present into the center of Earth This heated Earth further Lighter minerals migrated to Earth’s surface and formed

the crust lasted ~100 million years


Earth’s internal structure

Layers defined by composition • Crust• Mantle• Core

Layers defined by physical properties• Lithosphere• Asthenosphere• Mesosphere• Inner and Outer Core

Earth’slayered

structureFigure 1.14

Mass (kg) 5.976e+24

Mass (Earth = 1)

Equatorial radius (km) 6,378.14

Equatorial radius (Earth = 1) 1.0

Mean density (gm/cm^3) 5.515

Mean distance from the Sun (km) 149,600,000

Mean distance from the Sun (Earth = 1) 1.0000

Rotational period (days) 0.99727

Rotational period (hours) 23.9345

Orbital period (days) 365.256

Mean orbital velocity (km/sec) 29.79

Orbital eccentricity 0.0167

Tilt of axis (degrees) 23.45

Orbital inclination (degrees) 0.000

Equatorial escape velocity (km/sec) 11.18

Equatorial surface gravity (m/sec^2) 9.78

Visual geometric albedo 0.37

Mean surface temperature 15°C

Atmospheric pressure (bars) 1.013

Atmospheric composition Nitrogen 77Oxygen 21

Earth Stats

The face of Earth

Earth’s surface • Continents• Oceans

Continents• Mountain belts

• Most prominent feature of continents• The stable interior

• Also called a craton – composed of shields and stable platforms

The face of Earth

Ocean basins• Continental margins

• Includes the continental shelf, continental slope, and the continental rise

• Deep-ocean basins• Abyssal plains• Oceanic trenches • Seamounts

The face of Earth

Ocean basins• Oceanic ridge system

• Most prominent topographic feature on Earth• Composed of igneous rock that has been

fractured and uplifted

End of Chapter 1

Rocks and the rock cycle

Basic rock types• Igneous rocks

• Cooling and solidification of magma (molten rock) • Examples include granite and basalt

• Sedimentary rocks• Accumulate in layers at Earth’s surface • Sediments are derived from weathering of

preexisting rocks


Basic rock types• Sedimentary rocks

• Examples include sandstone and limestone• Metamorphic rocks

• Formed by “changing” preexisting igneous, sedimentary or other metamorphic rocks

• Driving forces are increased heat and pressure• Examples include gneiss and marble


The Rock Cycle: One of Earth’s subsystems• The loop that involves the processes by which

one rock changes to another • Illustrates the various processes and paths as

earth materials change both on the surface and inside the Earth

Therockcycle

Figure 1.21

Intro Geology

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