Historical Geology: Evolution of the Earth and Life Through Time

6th edition

Reed Wicander and James S. Monroe

The Dynamic and Evolving Earth

Chapter 1

The Movie of Earth’s History• What kind of movie would we have

– if it were possible to travel back in time – and film Earth’s history– from its beginning 4.6 billion years ago?

• It would certainly be a story of epic proportions– with incredible special effects – a cast of trillions– a plot with twists and turns – and an ending that is still a mystery!

• Although we cannot travel back in time, – the Earth’s history is still preserved – in the geologic record

Subplot: Landscape History• In this movie we would see

– a planet undergoing remarkable change as – continents moved about its surface– ocean basins opened and closed– mountain ranges formed along continental margins

or where continents collided• The oceans and atmospheric circulation

patterns would – shift in response to moving continents– causing massive ice sheets to form, grow, and then

melt away• Extensive swamps or vast interior deserts

– would sweep across the landscape

Subplot: Life’s History

• We would also witness – the first living cells evolving– from a primordial organic soup – between 4.6 and 3.6 billion years ago

• Cell nuclei would evolve, – then multicelled soft-bodied animals– followed by animals with skeletons and then

backbones

• The barren landscape would come to life as– plants and animals moved from their watery home.– Insects, amphibians, reptiles, birds and mammals – would eventually evolve.

Earth is a Dynamic and Evolving Planet

• Changes in its surface

• Changes in life

At the End of the Movie

• The movie’s final image is of Earth, – a shimmering blue-green oasis – in the black void of space– and a voice-over says,

• “To be continued.”

The Movie’s Theme

• Every good movie has a theme, – and The History of Earth is no exception.

• The major theme is that Earth is complex and dynamic

• Three interrelated themes sub-themes run throughout this epic:

• The first is that Earth’s outermost part – is composed of a series of moving plates

• Plate tectonics

– whose interactions have affected its physical and biological history.

The Movie’s Theme

• The second is that Earth’s biota – has evolved or changed throughout its history

• Organic evolution

• The third is that physical and biological changes – have occurred over long periods of time

• Geologic or Deep Time

• Three interrelated themes – are central to our understanding and appreciation– of our planet’s history.

Earth is a System of Interconnected Subsystems

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

Interactions in Earth’s Subsystems

This course is about historical geology

What is Geology?

• From the Greek – geo (Earth) logos (reason)

• Geology is the study of Earth

• Physical geology studies Earth materials,– such as minerals and rocks– as well as the processes operating within Earth

and on its surface

Historical Geology

• 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

• William Smith, an English surveyor/engineer– used his study of rock sequences and fossils– to predict the kinds and thicknesses of rocks – to be excavated in the construction of canals

Scientific Method

• The scientific method – an orderly and logical approach

– involves gathering and analyzing facts or data

• A hypothesis – is a tentative explanation

– to explain observed phenomena

• Scientists make predictions using hypotheses– then they test the predictions

• After repeated tests, – if one hypothesis continues to explain the phenomena,

– scientists propose it as a theory

Formulation of Theories

Theory

• colloquial usage: speculation or conjecture

• scientific usage – coherent explanation for one or several related

natural phenomena – supported by a large body of objective evidence

Origin of the Universe

• The Big Bang – occurred approximately 14 billion years ago– is a model for the evolution of the universe

Evidence for the Big Bang

• Universe is expanding– Galaxies are receding from each other, and

produce a red spectral shift• Doppler Effect

Evidence for the Big Bang

• Universe is expanding

• Pervasive background radiation of 2.7 Kelvin above absolute zero – the afterglow of the Big Bang

Evidence for the Big Bang

• How do we determine the age of the universe?– measure the rate of expansion – backtrack to a time when the galaxies were all

together at a single point

Big Bang Model

• When the universe began– All matter and energy were compressed

• infinitely small high-temperature and high-density state

– Time and space were set at zero

• During 1st second:– The four basic forces separated

• gravity, electromagnetic force, strong nuclear force, weak nuclear force

– Enormous expansion occurred

Big Bang Model, continued

• After 30 minutes, nuclear reactions had completely ended

• The universe’s mass consisted of almost entirely hydrogen and helium nuclei

• Continued expansion and cooling produced stars and galaxies

• The composition of the universe changed– Heavier elements are formed during stars’

deaths

Features of Our Solar System

• Part of the Milky Way Galaxy• Sun• 8 planets

– one dwarf planet, Pluto

• 153 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

Relative Sizes of the Sun and Planets

Solar System Configuration

Origin of Our Solar System

Solar nebula theory

• formed a rotating disk

• concentrated 90% of material in center part of disk

• forming solar nebula – with an embryonic Sun – surrounded by a rotating cloud

• cloud of gases and dust

• Planetesimals formed – and collided and grew in size and mass

Embryonic Sun and Rotating Cloud

The Planets

• Terrestrial Planets– Mercury – Venus– Earth– Mars

• small, composed of rock and metallic elements

• Jovian Planets– Jupiter – Saturn– Uranus– Neptune

• large, composed of hydrogen, helium, ammonia, methane; condense at low temperatures

Earth’s Very Early History

• About 4.6 billion years ago, early Earth was probably – cool– with uniform composition/density– Composed mostly of silicates, and – iron and magnesium oxides

• The temperature increased because of– meteorite impacts– gravitational compression– radioactive decay

• Iron and nickel melted and Earth’s homogeneous composition disappeared

Earth’s Differentiation

• Differentiation = segregated into a series of concentric layers of differing composition and density

• Molten iron and nickel sank to form the core

• Lighter silicates flowed up to form mantle and crust

Earth—Dynamic Planet

• Earth is a dynamic planet– The size, shape, and geographic distribution

– of continents and ocean basins have changed through time

– The composition of the atmosphere has evolved

– Life-forms existing today differ from those that lived in the past

Earth’s Interior Layers

• Mantle– 83% volume– composed largely of

peridotite– dark, dense igneous

rock, rich in iron and magnesium

• Core– Solid inner region, liquid

outer region– iron and a small amount of

nickel

• Crust– Continental (20-90

km thick)– Oceanic (5-10 km

thick)

Earth’s Interior Layers

• Crust– Continental (20-90 km

thick)– Oceanic (5-10 km thick)

• Mantle– 83% volume– composed largely of

peridotite– dark, dense igneous

rock, rich in iron and magnesium

• Core– Solid inner region, liquid

outer region– iron and a small amount of

nickel

• Lithosphere– solid upper mantle

and crust

• Asthenosphere– part of upper

mantle

– behaves plastically and slowly flows

Earth’s Interior Layers• Lithosphere

– solid upper mantle and crust

• Asthenosphere– part of upper

mantle– behaves plastically

and slowly flows

– broken into plates that move over the asthenosphere

Earth’s Crust• 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 and

gabbro

Plate Tectonic Theory

• Lithosphere is broken into individual pieces or plates

• Plates move over the asthenosphere – as a result of underlying convection cells

Modern Plate Map

Plate Tectonic Theory

• Plate boundaries are marked by– Volcanic activity– Earthquake activity

• At plate boundaries – plates diverge,– plates converge,– plates slide sideways past each other

Plate Tectonic Theory

• Types of plate boundaries

Plate Tectonic Theory

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 and Earth Systems

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

olid

Ear

thA

tmos

pher

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

Plate Tectonics and Earth Systems

Continental arrangement affects ocean currentsRate of spreading affects volume

of mid-oceanic ridges and hence sea levelPlacement of continents may contribute

to the onset of ice agesHyd

rosp

here

Bio

sphe

re Movement of continents creates corridors or barriers to migration, the creation of ecological niches, and transport of habitats into

more or less favorable climates

Theory of Organic Evolution

• Provides a framework – for understanding the history of life

• Charles Darwin’s – On the Origin of Species by Means of Natural

Selection, published in 1859,

– revolutionized biology

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 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 – seconds, hours, days, years

• Ancient human history– hundreds or thousands of years ago

• Geologic history– millions, hundreds of millions, billions of years

Geologic Time Scale

• Resulted from the work of many 19th century geologists who – gathered information – from numerous rock exposures, and– constructed a sequential chronology – based on changes in Earth’s biota through time

• Ages subsequently were assigned to the time scale– using radiometric dating techniques

Geologic Time Scale

Uniformitarianism• Uniformitarianism is a cornerstone of geology

– 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 through time

How Does the Study of Historical Geology Benefit Us?

• Survival of the human species – depends on understanding – how Earth’s various subsystems – work and interact

• By studying what has happened in the past – on a global scale, – and try to determine how our actions – might affect the balance of subsystems in the future

We “Live” Geology

• 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

Summary

• Earth is a system – of interconnected subsystems

• Geology is the study of Earth• Historical geology is the study

– of the origin and evolution of Earth

• Scientific method is – an orderly, logical approach to explain phenomena,

– using data,

– formulating and testing hypotheses

– proposing theories

• Universe began with – a Big Bang 14 billion years ago

Summary

• Solar system formed 4.6 billion years ago – by condensation and gravitational collapse – of a rotating interstellar cloud

• Earth formed 4.6 billion years ago – as a swirling eddy in the solar system nebula

• Earth is differentiated into layers – the oceanic and continental crust, mantle and

core, – with the upper mantle and crust – making up the solid lithosphere – which overlie the plastic asthenosphere

Summary

• Lithosphere is broken into plates – that diverge, converge and – slide sideways past each other

• Plate tectonics is a unifying theory– that helps explain features and events – including volcanic eruptions, – earthquakes, and formation of mountain ranges

• Central thesis of organic evolution is – that all living organisms evolved – from organisms that existed in the past

• An appreciation – of the immensity of geologic time – is central to understanding Earth’s evolution

Summary

• Uniformitarianism holds that the laws – of nature have been constant through time

• Geology is an integral part of our lives – and our standard of living depends – on our use of natural resources – that formed over millions and billions of years