Lecture 2nd

The Dynamic and

Evolving Earth

Earth

• Changes in its surface

• Changes in life

Atmosphere (air and gases) Hydrosphere (water and oceans) Biosphere (plants and animals) Lithosphere (Earth’s rocky

surface) Interior (mantle and core)

Gases from

respiration

Transport

of seeds and

spores

Wind erosion, transport

of water vapor for

precipitation

Mountains

divert air

movements

Source of sediment

and dissolved

material

Water

and glacial

erosion, solution

of minerals

• In historical geology we study

– changes in our dynamic planet

– how and why past events happened

– implication for today’s global ecosystems

• Principles of historical geology

– not only aid in interpreting Earth’s history

– but also have practical applications

The Big Bang

occurred 15 billion years ago

and is a model for the beginning of the universe

Universe is expanding

How do we determine the age?

measure the rate of expansion

backtrack to a time when the galaxies were all together at a single point

Initial state:

No time, matter or space existed

There is no “before the Big Bang”

Universe consisted of pure energy

During 1st second:

Very dense matter came into existence

The three basic forces separated

gravity, electromagnetic force, nuclear forces

Enormous expansion occurred

300,000 years later:

atoms of hydrogen and helium formed

light (photons) burst forth for the first time

During the next 200 million years:

Continued expansion and cooling

Stars and galaxies began to form

Elements heavier than hydrogen and helium began to form within stars by nuclear fusion

In a spiral arm of the Milky Way Galaxy

Sun

9 planets

101 known moons (satellites)

a tremendous number of asteroids most orbit the Sun between the orbits of Mars

and Jupiter

millions of comets and meteorites

interplanetary dust and gases

Solar nebula theory

• formed a rotating disk

• condensed and collapsed due to gravity

• forming solar nebula – with an embryonic Sun

– surrounded by a rotating cloud

• cloud of gases and dust

Terrestrial/Rocky Planets

Mercury Venus Earth Mars

small, composed of rock, with metal cores

• Jovian/Gaseous

Planets – Jupiter

– Saturn

– Uranus

– Neptune

• large, composed of hydrogen, helium, ammonia, methane, relatively small rocky cores

Started out cool about 4.6 billion years ago probably with uniform composition/density

Mostly: silicate compounds

iron and magnesium oxides

Temperature increased. Heat sources: meteorite impacts

gravitational compression

radioactive decay

Heated up enough to melt iron and nickel

Differentiation = segregated into layers of differing composition and density

• Early Earth was

probably uniform

• Molten iron and

nickel sank to form the core

• Lighter silicates flowed up to form mantle and crust

Impact by Mars-sized or larger planetesimal with young Earth 4.6 to 4.4 billion

years ago

– ejected large

quantity of hot

material,

– and formed the

Moon

Most of the lunar material came from the

mantle of the colliding planetesimal

The material cooled and

crystallized

into lunar layers

Earth was also subjected

to the same meteorite barrage that pock-marked

the Moon

Why isn’t Earth’s surface also densely

cratered?

Because Earth is a dynamic and evolving planet

Craters have long since been worn away

Crust - 5-90 km thick continental and

oceanic

• Mantle – composed largely

of peridotite

– dark, dense igneous rock

– rich in iron and magnesium

• Core – iron and a small

amount of nickel

Crust - 5-90 km thick continental and

oceanic

• Mantle – composed largely

of peridotite

– dark, dense igneous rock

– rich in iron and magnesium

• Core – iron and a small

amount of nickel

• Lithosphere – solid upper mantle

and crust

• Asthenosphere – part of upper

mantle

– behaves plastically and slowly flows

• Lithosphere/Geosphere

– solid upper mantle and crust

• Asthenosphere – part of upper

mantle

– behaves plastically and slowly flows

– broken into plates that move over the asthenosphere

outermost layer continental (20-90 km thick)

– density 2.7 g/cm3

– contains Si, Al

• oceanic (5-10 km thick)

– density 3.0 g/cm3

– composed of basalt

Lithosphere is broken into individual pieces called plates

• Plates move over the asthenosphere

– as a result of underlying convection cells

At plate boundaries Volcanic activity occurs

Earthquakes occur

Movement at plate boundaries plates diverge

plates converge

plates slide sideways past each other

Types of plate boundaries

Divergent plate boundary

Divergent plate boundary Mid-oceanic

ridge Transform plate boundary

Continental-continental convergent plate boundary

Continental-oceanic convergent plate boundary

Oceanic-oceanic convergent plate boundary

Trench

Influence on geological sciences:

Revolutionary concept

major milestone

comparable to Darwin’s theory of evolution in biology

Provides a framework for

interpreting many aspects of Earth on a global scale

relating many seemingly unrelated phenomena

interpreting Earth history

Plate tectonics is driven by convection in the mantle and in turn drives mountain building and associated igneous and metamorphic activity

So

lid

Ear

th

Atm

osp

her

e Arrangement of continents affects

solar heating and cooling,

and thus winds and weather systems

Rapid plate spreading and hot-spot activity

may release volcanic carbon dioxide

and affect global climate

Continental arrangement affects ocean currents Rate of spreading affects volume

of mid-oceanic ridges and hence sea level

Placement of continents may contribute to the onset of ice ages

Hyd

rosp

her

e B

iosp

her

e Movement of continents creates corridors

or barriers to migration,

the creation of ecological niches,

and transport of habitats into

more or less favorable climates

The Earth’s External Heat Engine Isostatic adjustment (allows exposure of crust) Weather patterns influenced by solar forces Solar heating of air creates wind; wind creates ocean

waves; moist air cools allowing rain and snow; rain flows downhill in streams, lakes, rivers, seas; glaciers accumulate and move downhill due to gravity

Erosion takes place where moving water, ice, or wind loosens and removes material

This loose material is called Sediment, it is the product of the breakdown of rock

Provides a framework

for understanding the history of life

Darwin’s

On the Origin of Species by Means of Natural

Selection, published in 1859,

revolutionized biology

The fossil record provides perhaps

the most compelling evidence

in favor of evolution

Fossils are the remains or traces

of once-living organisms

Fossils demonstrate that Earth

has a history of life

From the human perspective time units are in

seconds, hours, days, years

Ancient human history

hundreds or even thousands of years

Geologic history

millions, hundreds of millions, billions of years

Resulted from the work of many 19th century geologists who

pieced together information

from numerous rock exposures,

constructed a sequential chronology

based on changes in Earth’s biota through time

The time scale was subsequently dated in years

using radiometric dating techniques

Uniformitarianism is a cornerstone of geology is based on the premise that present-day processes

have operated throughout geologic time

The physical and chemical laws of nature have remained the same through time

To interpret geologic events from evidence preserved in rocks

we must first understand present-day processes

and their results

Rates and intensities of geologic processes may have changed with time

Survival of the human species

depends on understanding

how Earth’s various subsystems

work and interact

Study what has happened in the past,

on a global scale,

to try and determine how our actions

might affect the balance of subsystems in the future

Our standard of living depends directly on

our consumption of natural resources

resources that formed millions and billions of years ago

How we consume natural resources

and interact with the environment determines

our ability to pass on this standard of living

to the next generation

Without discussing minerals and rocks it is difficult to talk about geology

Mineral is a: Crystalline solid Formed through geologic processes Specific chemical composition

• Mineraloids • Types of minerals

• Rock – forming minerals • Common minerals consists of Feldspar group,

pyroxene group, amphibole group, quart – mica group, olivine, garnet group, clay minerals, non- silicates (calcite, dolomite, gypsum) while much less common are halite, diamond, gold, hematite, magnetite, chalcopyrite, sphalerite and galena

• Ore – minerals • Gangue minerals • Industrial minerals

Color

Streak

Luster (metallic & non – metallic {admantine, vitreous, resinous, greasy and pearly})

Transparency (transparent , translucent and opaque)

Fracture

Hardness (Moho & Indentation/Vicker’s scale)

Specific gravity

Taste

Odour

Feel

Form

Magnetism

Naturally formed

Consolidated material

Composed of grains of one or more minerals

Rock Cycle • Progressive transformation of earth materials

from one rock type to another

• Internal and external forces of earth are the major cause of this cycle

Igneous

Sedimentary

Metamorphic

Mineralisation