Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 1:
THE EARTH SYSTEM
© 2011 by W. H. Freeman and Company
Chapter 1:
The
Earth
System
About the Earth System
• All parts of our planet and all of the
interaction of those parts comprise
the Earth System.
• Earth system is an open system.
• Geosystems include: climate, plate
tectonics, and the geodynamo.
Lecture Outline
1. The scientific method
2. Geology as a science
3. Earth’s shape and surface
4. Discovery of a layered Earth
5. Earth as a system of interacting
components
6. Overview of geologic time
1. The Scientific Method
The goal:
explain how the
universe works
1. The Scientific Method
Observation and experimentation
Development of an hypothesis or multiple
hypotheses as tentative explanation(s)
Testing (challenging) and experimentation to
eliminate hypotheses or revise them
Scientific theory – a coherent set of hypotheses
that explains some aspect of nature
Scientific model – based on many hypotheses
and theories
2. Geology as a Science
Major questions in geology involve processes that
operate on large scales and over long time
periods.
Field observations are supplemented by
laboratory experiments.
There are many subfields of geology, including:
Oceanography, Ecology, Geophysics,
Geochemistry, and Geobiology.
In addition, there are others, including Planetary
Science.
2. Geology as a Science
A special aspect:
probing Earth’s long
history – studying
the geologic record
2. Geology as a Science
Principle of
uniformitarianism:
The present is the key
to understanding the
past.
2. Geology as a Science
Process comparison: slow versus rapid
The most recent layer
of sediment is about
250 million years old.
The explosive impact of a
meteorite created this
1.2-km-wide crater in just
a few seconds.
The rocks at the bottom of
the Grand Canyon are 1.7–2.0
billion years old.
3. Earth’s Shape and Surface
Geodesy – study of Earth’s shape and surface
• Ancient Greek scholar Eratosthenes’ work showed
that the Earth was spherical.
• Modern research shows that the Earth is not a
perfect sphere.
• Earth’s topography (surface elevation) ranges nearly
20 km from highest to lowest.
• Sea level – reference level for all Earth surface and
seafloor elevations.
Topography
4. Discovery of a Layered Earth
Seismic waves – illuminate Earth’s interior
• Compression and shear waves behave
differently and are bent or absorbed at layer
boundaries within the Earth.
Earth’s interior is layered according to
density
• Surface rock density is less than 3.5 g/cm3.
• Whole Earth density is 5.5 g/cm3.
3
4. Discovery of a Layered Earth
Crust
Crust
Mantle
Crust
Mantle
Liquid iron
outer core
Crust
Mantle
Liquid iron
outer core
Solid iron
inner core
4. Discovery of a Layered Earth
The crust: continents are made of lighter
rock and thus literally “float” on material
of higher density.
0 (km)
10
20
30
40
50
Oceanic crust
(3.0 g/cm3)
Continental crust
(2.8 g/cm3)
Mantle
(3.4 g/cm3)
Horizontal distance not to scale
Moho
discontinuity
Less dense continental
crust floats on denser
mantle.
0 (km)
10
20
30
40
50
Oceanic crust
(3.0 g/cm3)
Continental crust
(2.8 g/cm3)
Mantle
(3.4 g/cm3)
Horizontal distance not to scale
Moho
discontinuity
Less dense continental
crust floats on denser
mantle.
0 (km)
10
20
30
40
50
Oceanic crust
(3.0 g/cm3)
Continental crust
is less dense than
oceanic crust.
Continental crust
(2.8 g/cm3)
Mantle
(3.4 g/cm3)
Horizontal distance not to scale
Moho
discontinuity
4. Discovery of a Layered Earth
Abrupt changes in
density between
Earth’s major interior
layers are caused by
changes in the
chemical composition
of those layers.
5. Earth as a System of Interacting
Components
Earth system – all parts of Earth and the
interactions of the parts
• climate system
• plate tectonics system
• geodynamo system
Earth is an open system.
• exchanges mass and energy with the
rest of the cosmos
Earth system:
Interactions
of the climate,
plate tectonic,
and
geodynamo
systems.
The plate tectonics system: How does
the heat energy inside the Earth move
and thus affect the crustal plates?
Convection causes
hot water to rise…
...where it cools,
moves laterally,
sinks,…
Hot matter from the
mantle rises,…
Plate
…warms,
and rises
again.
…causing plates to
form and diverge.
Plate
Where plates
converge, a
cooled plate
is dragged
under…
…sinks, warms,
and rises again.
The geodynamo system: Rapid motion
of the liquid outer core stirs up electrical
flow in the solid (iron) inner core –
causing Earth’s magnetic field.
Earth is an open system.
Sun
The Sun drives
Earth’s external
engine.
Sun
The Sun drives
Earth’s external
engine.
Sun
Solar energy is
responsible
for our climate
and weather.
The Sun drives
Earth’s external
engine.
Sun
Solar energy is
responsible
for our climate
and weather.
Earth’s internal
engine is powered
by trapped heat…
The Sun drives
Earth’s external
engine.
Sun
Solar energy is
responsible
for our climate
and weather.
Earth’s internal
engine is powered
by trapped heat…
…and radioactivity
in its interior.
The Sun drives
Earth’s external
engine.
Solar energy is
responsible
for our climate
and weather.
Earth’s internal
engine is powered
by trapped heat…
Sun
Heat radiating from Earth
balances solar input and
heat from interior.
…and radioactivity
in its interior.
The Sun drives
Earth’s external
engine.
Solar energy is
responsible
for our climate
and weather.
Earth’s internal
engine is powered
by trapped heat…
…and radioactivity
in its interior.
Sun
Heat radiating from Earth
balances solar input and
heat from interior.
Meteors move mass from
the cosmos to Earth.
6. Overview of Geologic Time
6. Overview of Geologic Time
4.6 billion years ago – formation of solar system
3.5 billion years ago – formation of geodynamo;
first known fossils (bacteria)
2.7 billion years ago – oxygen begins to build up
in atmosphere
2.5 billion years ago – large continents in crust
2.0 to 1.0 billion years ago – more complex life
like algae evolved
6. Overview of Geologic Time
6. Overview of Geologic Time
600 million years ago – first animals
542 million years ago – evolutionary “big bang”
443 million years ago – first mass extinction of
life
420 million years ago – first land mammals
359, 251, and 200 million years ago – mass
extinctions of life
125 million years ago – first flowering plants
6. Overview of Geologic Time
65 million years ago – last mass extinction
(death of the dinosaurs and many other species)
5 million years ago – appearance of first
hominids
200,000 years ago – appearance of Homo
sapiens
6. Overview of Geologic Time
Key terms and concepts
Asthenosphere
Climate
Climate system
Convection
Core
Crust
Earth system
Fossil
Geodynamo
Geologic record
Geology
Geosystem
Inner core
Lithosphere
Key terms and concepts
Magnetic field
Mantle
Outer core
Plate tectonic system
Principle of uniformitarianism
Scientific method
Seismic wave
Topography