ESC 102Evolution of Earth and Life

HistoricalGeology

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 UniverseDetermine 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

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 DifferentiationDifferentiation = segregated into layers of

differing composition and densityEarly Earth was

probably uniformAfter 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

Impact hypothesis for 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?

Major elements on

Earth

Top 4 most abundant elements:OxygenSilicon

aluminum

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

Modern Plate MapActive 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 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 EvolutionProvides a framework for understanding the

history of lifeDarwin’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

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