Lecture 1. The Earth:
How and Why We Study it
Introduction to the Earth System
EAS 2200
Today’s Plan
 Organizational matters
 Plan of the course
 Why study the Earth?
 How we study the Earth
 How science works
 Earth science - uniquely historical
 Origins of Earth Science, Early Concepts
 Geologic Time
 Thinking about geologic time
Organizational Matters
Syllabus & Course Plan
Note dates for prelims
Textbook
Grading
Plan of the Course
 Introduction/Origin of the Earth
 Earth Materials & Their Properties
 Earth from Inside Out
 Structure of the Earth
 Plate Tectonics: Earthquakes, Volcanoes, Deformation
 Reshaping the Face of the Earth: Water, Ice, Wind,
Erosion and Deposition
 Evolution of Life, Atmosphere, and Climate
 The Atmosphere
 The Oceans
 The Biosphere
 Changing Climate on the Modern Earth
Goals for This Course
 Introduce you to study of the Earth as an
integrated system.
 Virtually every aspect of the Earth affects and
is affected by every other aspect of the Earth.
Examples:
Geological processes affect climate
Climate affects geological processes
Life affects climate – climate affects life
Life is a geological process!
 Prepare you for advanced courses in
Earth Science
 Expose you to concepts, vocabulary, etc. that
you’ll need in advanced courses.
Why study the Earth?
 Resource Exploitation
 Environmental Protection/Preservation
 Curiosity – The Earth is a fascinating
place!
 Only planet where 3 states of matter are
known to exist continuously at the surface.
 It is continually geologically active (unlike the
other terrestrial planets) in this solar system.
 It is the only planet known to have life.
How we study the Earth:
How science works
The fundamental postulate
Observations, hypotheses, and
skepticism
Parsimony
Scientific Progress
Math and Science
The Fundamental Postulate
 Every phenomenon has an explanation based
ultimately on the fundamental laws.
 “Raffiniert ist der Herr Gott, aber boshaft ist er
nicht.” (God is subtle, but he is not malicious)– Einstein
 Put another way, there is no such thing as
magic, only phenomena we don’t understand.
 (The fundamental laws do allow for chance
events, hence the future is not preordained.)
 It seems Einstein was wrong when he said, “Gott
würfelt nicht” (God does not play dice).
 While the fundamental laws do not always allow us to
predict the outcome of events, they do allow us
Currency of Science
 Science deals in only 2 quantities:
 Observations
 Hypotheses
– paradigms
In Science, Nothing is
Sacred!
 Science deals only in observations and
hypotheses and both can be wrong.
 Therefore, there is no such thing as a
scientific fact.
 Even the wildest theories can turn out to
be right (examples: relativity, plate
tectonics), and seemingly certain ideas
wrong (invariance of time, fixed
continents).
 Consequently, question everything.
 (Including what you learn in this class!)
Observations
 The most basic building block of science.
 Also known as data, results, experiments,
“measurements”, etc.
 Might be an experiment in a physics
laboratory, a chemical analysis, a series
of ocean temperature measurements, or
a seismogram.
 How can we tell whether observations are
wrong or not?
 Independently replicate them.
 But replication does not guarantee that an
Hypotheses
 These too go by various names: theories, models,
laws, etc.
 Hypotheses are, very simply, just attempts to
explain observations.
 How to we know if a hypothesis is right?
 A hypothesis is tested by comparing its predictions with
additional observations, i.e., new experiments, new
measurements, etc.
 If it passes the test, fine (but it could always fail the next
one).
 If it fails, it is modified or discarded. The latter
sometimes leads to scientific revolutions (e.g., relativity
and quantum physics, evolution, plate tectonics).
Occam’s Razor or
Parsimony
Which theory do we accept when
two theories explain the same
phenomenon equally well?
The principle is that the theory that
explains the greatest range of
phenomena in the simplest manner
is preferred – in general.
Don’t make nature more complicated
than it already is!
Scientific Progress
 Although breakthroughs occasionally
occur, most scientific progress is
piecemeal with new observations
suggesting minor adjustments to
theories.
 New observations sometimes suggest new
theories.
 New theories & paradigms often suggest new
observations.
 Often, key observations must await new
technical or instrumental advances.
 Sometimes, new technical advances lead by
chance to important new observations.
Mathematics and Science
 A curious and remarkable thing is that the
universe can sometimes be quantified and
described with great precision with
mathematics.
 This was perhaps Newton’s greatest contribution,
and the most important thing that the Greeks
missed.
 Even when there is inherent uncertainty, the
uncertainty itself can be precisely quantified.
 While in practice, some things remain too
complex for us to describe mathematically,
there is in theory a mathematical description.
The Special Nature of Earth
Science
 The Earth we see today is the
consequence not only of the fundamental
laws, but also of a long sequence of
events, which we were not around to
observe.
 Earth science is a science where history
matters (also true of astronomy and
biology).
 One challenge is to deduce that history.
 Another is to use this history (in
partnership with lab measurements and
Science and You
 While this course will be devoted to informing
you of what we know about the Earth (or what
we think we know), the main focus of science is
research, i.e., what we don’t know.
 There is still much that we don’t know. Some,
maybe even much, of what we think we know
will turn out to be wrong. Critical research skill
is to learn how to learn more effectively…
 In the next decade or two, the torch will pass to
your generation to push the frontiers of
knowledge forward. There is abundant
opportunity for you to become part of the
scientific enterprise.
Origins of Earth Science
 Geology originated in the 16th century with Georg
Bauer (Agricola) (1494-1555) and Nicolas Steno
(1638-1686) who observed that rocks were laid
down in definite layers, or strata, and that these
layers occurred in a consistent order over a wide
area.
 Leonardo Da Vinci made accurate reconstructions
and maps of the evolution of the Arno River
through time
 Modern physical science, however, begins with
Galileo Galilei (1564-1642) and Issac Newton
(1643-1727), who deduced fundamental laws of
motion and established the mathematical basis of
James Hutton and Modern
Earth Science
 James Hutton (1726-1797) is viewed by many Englishspeakers as the founder of modern geology.
 Important ideas
 Infinite expanse of geologic time
 Uniformitarianism — “What is, also was” hypothesis
 Recognized the role of internal energy to drive
geologic processes.
Hutton thought exclusively of heat, just one form of
energy, and he thought it derived from burning
coal.
 Recognized 3 ways in which rocks formed.
 Rain produced when air was cooled.
 Early thinking on evolution and natural selection.
Hutton & Plutonism
 Hutton recognized 3 classes of rocks
 Sedimentary
 Metamorphic
 Igneous
 Because he emphasized the need for internal
energy, even in the transformation of
sediment to sedimentary rock, he is often
thought of as a plutonist in opposition to the
neptunists led by Abraham Gottlob Werner
(1749-1817).
 Neptunists hypothesized all-encompassing ocean that
gradually receded while precipitating or depositing virtually
Hutton and Natural
“If an organised body is not in the situation and
circumstances best adapted to its sustenance
and propagation, then, in conceiving an
indefinite variety among the individuals of that
species, we must be assured, that, on the one
hand, those which depart most from the best
adapted constitution, will be most liable to
perish, while, on the other hand, those
organised bodies, which most approach to the
best constitution for the present circumstances,
will be best adapted to continue, in preserving
themselves and multiplying the individuals of
their race.”
Hutton as Meteorologist
 Hutton proposed that the amount of
moisture that air could hold increased
with temperature.
 Argued that when a cold and warm air
mass mixed, rain formed.
 Investigated rainfall and climate globally
and concluded that the rainfall is
regulated by the humidity of the air on
the one hand, and mixing of different air
currents in the higher atmosphere on the
other.
Hutton & Uniformitarianism
 “No powers are to be employed that are
not natural to the globe, no action to be
admitted except those of which we know
the principle.”
 In other words, the forces that shaped
the Earth in the past are the same that
are reshaping it today.
 (This is in some sense a corollary our
fundamental postulate). If taken too
strictly, it can become a straightjacket.
No mass extinctions? No Meteorite
impacts? No Flood basalts?
“no vestige of a
beginning--no prospect of
 Hutton envisioned
geologic time as
effectively infinite
 (but not quite infinite,
since he believed that
God created the Earth
specifically for human
habitation).
Unconformity at Siccar Point, Scotland
 Viewed geological
processes as
continuous, repeating
cycles; e.g., erosion,
sedimentation, uplift,
erosion, etc.
Geologic Time
How do we think about it?
Represent it?
Relative time (&fossils+evolution!!)
Principle of superposition
Correlation
Absolute time
Radioactive Decay: nature’s clock
Geologic Time: Important
Points
 The Earth has a history.
 It had a beginning (but Hutton was mostly
right - there is almost no vestige of it to be
found on Earth, the real vestiges are found
elsewhere in the solar system).
 The beginning profoundly affected the kind of
planet Earth would become.
 The scale of Geologic Time is vast: 4.56
billion years.
 This is nearly unimaginably long to humans.
 If all of Earth’s history were reduced to a year,
human existence would occupy the last 18
minutes; a human life would be 1/2 second.
Geologic Time - the Logarithmic
View
 Advantages/Rationale:
 We can determine
younger ages more
precisely.
 Record of younger
periods better
preserved - we know
them in more detail.
 Younger periods
(“Phanerozoic’) are
more interesting
biologically.
 Reflects history of
geological interest –
Geologic Time - the Spiral View
 Advantages/
Rationale
 Cycles are
important:
 Tides, day,
seasons, year,
Milankovitch
cycles, cycles of
extinction and
radiation, Wilson
cycles
 Despite the cycles,
the Earth and life
do not return to
the same point, but
evolve.
 Another reflection
Earth History - how do we
deduce it?
 If the Earth has a history, and human
existence and written history record only
a part of that, how do we deduce what
that history was?
 For example, why do we think life originated
in the seas? Why do many think the
dinosaurs were wiped out by an impact? Why
do we think North America and Europe were
once connected?
 The Earth’s history is recorded in its rocks.
 But how do we read that record?
Relative Time: Law of
Superposition
 Since sedimentary rocks form by things falling down
under gravity, a sequence of sediments must get younger
upward. This is known as the Law of Superposition,
deduced by Neils Stensen (Steno) in the 17th century.
Relative Time & Correlation
 No single sequence of
sedimentary rocks provides
a complete record of Earth
history. We need to deduce
Earth’s history by weaving
pieces of history into a
longer story. How do we do
this?
 Principle is that rocks
containing the same fossil
assemblage were deposited
at the same time.
 This procedure, called
correlation, was discovered
by William Smith in the early
19th century. (predating
formal theory of evolution!)
 Only good back to 540Ma
Building a Relative Time
Scale
Using correlation, we can determine the sequence in which
events occurred, but not the length of time this sequence
represents.
Radioactive Decay and
Nuclear Processes
 The revolution in physics that started at
the end of the 19th century – in particular
nuclear theory of matter – provided both
a means to measure geologic time and a
source of energy to power the Earth, the
Sun, and the Stars.
 Within a decade of the discovery of
radioactivity (and before Neils Bohr
published is nuclear model of the atom),
the first radiometric date showed the
Earth was far older than physicists
thought.
Types of Radioactive Decay
 Radioactive decay refers
to the transmutation of
one element into
another through loss
(or gain) of particles
from the atomic
nucleus. For example:
 Beta decay
 Nucleus emits electron
or positron
 Alpha decay
 Nucleus emits a helium
nucleus
Isotopes
 It is not elements per se that undergo
radioactive decay, but specific isotopes of some
elements.
 Isotopes are atoms of an element that differ only
in the number of neutrons in the nucleus.
 Examples
 Isotopes are written as the chemical symbol, with the
mass number pre-superscripted.
 12C (6 protons, 6 neutrons) and 13C (6 protons, 7
neutrons) are stable, but 14C (6 protons, 8 neutrons)
decays to 14N (7 protons, 7 neutrons).
 238U and 235U are both unstable and undergo a series
of decays eventually becoming 206Pb and 207Pb.
Radioactive and Radiogenic
Elements
Absolute Geologic Time
Modern measurement of absolute
geologic time is now based on
radioactive decay.
Actually, it is usually based on the buildup of the new atoms produced by
radioactive decay (easier to measure what
is there than what is not; 14C is an
exception).
Radioactive decay is a process that
occurs at rates that are independent of
environmental influences (like
Key Dates in Earth’ History