Download The Geologic Time Scale

ESC 102
Evolution of
Earth and Life
Historical
Geology
Spring 2011
Earth Systems
can you identify them?
• When we view the
Earth from space
what Earth systems
are observable?
• What is most obvious?
• Are these systems
independent or do
they interact with one
another?
Systems = Spheres of the Earth
• Lithosphere: Earth’s solid rocky mass
• Hydrosphere: All of earth’s water
• Atmosphere: The thin gaseous layer
above Earth’s surface
• Biosphere: All of earth’s life forms
Three Themes tell the story of the
evolving Earth
 The Theory of Plate Tectonics
Solid Earth is composed of plates that move over Earth’s
surface.
The Theory of Organic Evolution
Earth’s biota – all living things – has evolved or changed
through history.
The Geologic Time Scale
Geologic processes take place within extensive geologic time ~ 4.6 billion years of Earth’s history.
Something Happened…..
James Hutton observed tilted
sedimentary layers overlain
by near-horizontal layers.
He realized that whatever
processes created this rock
outcrop must have taken
millions of years.
In 1785, published his
Theory of the Earth and is
considered founder of
modern geology.
• Charles Lyell wrote
“Principles of
Geology in 1830.
He furthered the work of
James Hutton:
concept of
Uniformitarianism
Rock layers reveal
sequences of events based
on processes that occur
today.
Historical Geology
applies geologic principles to
help predict and explain
Earth’s materials
• William Smith was an
English surveyor who
realized that rock types
and fossils occur in
repeated patterns. He was
able to predict rock
sequences that would be
encountered in
constructing canals
• Smith mapped the geology
of much of England.
(1815)
Smith’s map took many years to
complete and helped establish the
geologic time scale.
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Slide 12
Hypothesis or Theory?
• The scientific method brings an orderly and
logical approach to decoding geologic evidence.
• A hypothesis is a tentative explanation for
observations
• Scientists make predictions using hypotheses –
then they are tested
• After repeated testing, a theory may be proposed
• Some phenomena cannot be tested or explained
A theory is formed
• A theory is more than an “educated guess”
• A theory explains natural phenomena and
may relate several observations
• A theory is well-tested and well-supported
by objective evidence
• Examples include:
Plate Tectonics Theory
Theory of Organic Evolution
Where do scientists look for evidence
for the following?
• The origin and age of the universe
• The origin and age of the solar system
• The origin and age of the Earth and Moon
• The origin of life on Earth
• Evidence of plate movement on Earth
• Explanation for large scale extinctions on Earth
How old is the universe?
• When? Scientists believe the universe was
formed about 15 billion years ago
• How? The Big Bang is a model for the
“beginning” of the universe
• “Show me”! What is the evidence?
Evidence of the Big Bang
• Pervasive background radiation of 2.7o C
above absolute zero is observed in space
(-273o C
or -460o F)
“Afterglow” of
the Big Bang
discovered in
1965
As predicted, it was
cosmic microwave
radiation from .space
Evidence of the Big Bang
• Galaxies moving away – expanding universe
(proposed by Hubble)
Imagine the surface
of a balloon as it
is inflated. Locations
on the surface move
away from one another.ther.
Evidence of the Big Bang
Determine the Age of the Universe
Determine rate of expansion
“Back-model” to a time when the galaxies
would be together in the same space
Research
• A 7 year satellite observation project
mapped the cosmic microwaves in space
– Revealed the nature of many components
that had been predicted in various models.
• The WMAP project since 2002 has enabled
scientists to refine the age of the universe to 13.7
billion years and the “shape” of its surfaces.
Big Bang model
• Initial state: NO time, NO matter, NO space
– Universe was pure ENERGY
• During the FIRST second of time:
--very dense matter came into existence
--The four basic forces separated:
gravity
electromagnetic force
strong nuclear and weak nuclear forces
Enormous expansion occurred
Big Bang Model
• 300,000 years later:
– Atoms of hydrogen and helium formed
– Light (photons) burst forth for the first time
• Next 200 million years:
– Continued expansion
– Stars and galaxies began to form
– Elements heavier than hydrogen and helium began
to form within stars by nuclear fusiion
The formation
of the
solar system
9 billion years later…..
Origin of Our Solar System
Solar nebula theory
• cloud of gases and
dust
formed a rotating
• condensed
and
disk
collapsed due to
gravity
• forming solar nebula
– with an embryonic Sun
– surrounded by a rotating cloud
Embryonic Sun and Rotating Cloud
• Planetesimals have formed
– in the inner solar system,
– and large eddies of gas and dust
– remain far from the protosun
The planets formed with distinct
orbits around the sun.
Some planets have satellites
which orbit individual planets.
Solar Nebula
Theory
Is there Evidence?
The Hubble Telescope
image shows a solar
nebula as a
protoplanetary disk or
“proplyd” located in
Orion Nebula with
dozens of others. The
proto star is the bright
glow; dark area is a
dense molecular cloud.
This NASA image clearly shows that this star has 4 distinct
rings. These rings will eventually coalesce into solid bodies
called planets.
The Planets
Terrestrial Planets
Jovian Planets
 Mercury
 Venus
 Earth
 Mars
 Jupiter
 Saturn
 Uranus
 Neptune
 Small in size
 Composed of rock
 Metallic cores
 Large in size.
 Composed of hydrogen,
helium, ammonia, methane
 Small rocky cores
 Asteroid Belt
 Kuiper Belt
Pluto: no longer has planet
status
Relative Sizes of the
Sun and Planets
Earth’s Very Early History
Started out cool about 4.6 billion years ago
probably with uniform composition/density
Temperature increased. Heat sources were:
– meteorite impacts
– gravitational compression
– radioactive decay
Heated up enough to melt iron and nickel
within the newly formed Earth
The earth and moon were heavily
bombarded in Earth’s early history.
Earth’s Differentiation
Differentiation = segregated into layers of
differing composition and density
Early Earth was
probably uniform
After heating,
molten iron and
nickel sank to form
the core
Lighter minerals
flowed up to form
mantle and crust
Forming the Moon
• Impact by Marssized planetesimal
with early Earth
4.6 to 4.4 billion
years ago
Ejected a large quantity
of hot material that
cooled and coalesced to
form the moon
Impact hypothesis for moon
Most of the
lunar material
came from the
mantle of the
colliding
planetesimal
Moon is smaller than Earth and
cooled quickly.
Light colored surface areas are lunar
Highlands – heavily cratered.
evidence of massive meteorite
Bombardment
Mare: areas of lava flows more likely
due to impact than tectonics
Slide 8
Fig 1-5, p. 9
The material
cooled and
crystallized
into lunar
layers
Earth—Dynamic Planet
Earth was also subjected
to the same meteorite barrage
that pock-marked the Moon
Why isn’t Earth’s surface also densely
cratered?
Major
elements on
Earth
Top 4 most abundant
elements:
Oxygen
Silicon
aluminum
Earth’s Interior Layers
• Lithosphere
– solid upper mantle
and crust -broken into plates
that move over the
asthenosphere
• Asthenosphere
– part of upper
mantle
– behaves
plastically and
slowly flows
Plate Tectonics Theory
• Lithosphere is broken into individual
pieces called
plates
• Plates move over the asthenosphere
– as a result of underlying convection cells
Plate Tectonic Theory
• Movement at plate boundaries
– plates diverge
– plates converge
– plates slide sideways past each other
• At plate boundaries
– Volcanic activity occurs
– Earthquakes occur
Modern Plate Map
Active tectonic boundaries are in red
Plate Tectonic Theory
After decades of puzzling evidence, the theory
was developed in the1960s
• Provides a framework for
– interpreting many aspects of Earth on a global
scale
– and relating many seemingly unrelated
phenomena
– Key to interpreting Earth history
The “unifying theory of geology”
Plate Tectonics and
Earth Systems
Mechanism: Plate tectonics is driven by
convection in the mantle
and in turn drives mountain building
and associated igneous and metamorphic activity
Global effects of plate movement:
Arrangement of continents affects
solar heating and cooling,
winds and weather systems
Rapid plate spreading and hot-spot activity
may release volcanic carbon dioxide
and affect global climate
History of Earth
The history of the early earth through the
present is revealed mainly in the rock and
fossil records.
By applying principles of formation and
determining environments from life forms,
early interpretations about Earth’s land
masses and oceans have been made
Theory of Organic Evolution
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
– Provided the mechanism of natural selection
Central Thesis of Evolution
All present-day organisms
are related and descended from organisms that
lived during the past
Natural selection is the mechanism
that accounts for evolution
Natural selection results in the survival
to reproductive age of those organisms
best adapted to their environment
History of Life
• 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
Geologic Time
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
Geologic Time Scale
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:
The Present is the key to the past
• 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