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ESC 102 Evolution of Earth and Life Historical Geology Spring 2011.
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Transcript of ESC 102 Evolution of Earth and Life Historical Geology Spring 2011.
Earth Systemscan 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 ofUniformitarianism
Rock layers reveal sequences of events based on processes that occur today.
Historical Geologyapplies 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.
Slide 12 Fig 1-9, p. 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 surfaceof a balloon as itis 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
9 billion years later…..
The formation of the
solar system
Origin of Our Solar SystemSolar nebula theory
• condensed and collapsed due to gravity
• forming solar nebula – with an embryonic Sun – surrounded by a rotating cloud
• cloud of gases and dustformed a rotating disk
• Planetesimals have formed – in the inner solar system,
– and large eddies of gas and dust – remain far from the protosun
Embryonic Sun and Rotating Cloud
The planets formed with distinctorbits 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 PlanetsTerrestrial Planets Mercury Venus Earth Mars
Small in size Composed of rock Metallic cores
Asteroid Belt
Jovian Planets Jupiter Saturn Uranus Neptune
Large in size. Composed of hydrogen,
helium, ammonia, methane Small rocky cores
Kuiper Belt Pluto: no longer has planet status
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
Earth’s DifferentiationDifferentiation = 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 Mars-sized 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
Slide 8 Fig 1-5, p. 9
Most of the lunar materialcame from the mantle of the colliding planetesimal
The material cooled andcrystallized into lunar layers
Moon is smaller than Earth and cooled quickly.Light colored surface areas are lunarHighlands – heavily cratered.evidence of massive meteorite BombardmentMare: areas of lava flows more likely due to impact than tectonics
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?
Earth’s Interior Layers• Lithosphere
– solid upper mantle and crust -- broken into plates that move over the
• Asthenosphere– part of upper
mantle– behaves
plastically and slowly flows
asthenosphere
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
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 systemsRapid 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 pastNatural 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 inseconds, hours, days, years
Ancient human historyhundreds or even thousands of years
Geologic historymillions, 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