Post on 19-Jun-2015
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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