Geography ch12 part 1

Chapter 12 Lecture
© 2015 Pearson Education, Inc.
The Dynamic
Planet
Geosystems
9th Edition

Learning Objectives
• Distinguish between the endogenic and exogenic systems
that shape Earth, and name the driving force for each.
• Explain the principle of uniformitarianism, and discuss the
time spans into which Earth’s geologic history is divided.
• Depict Earth’s interior in cross section, and describe each
distinct layer.
• Describe the three main groups of rock, and diagram the
rock cycle.
• Describe Pangaea and its breakup, and explain the physical
evidence that crustal drifting is continuing today.
• Draw the pattern of Earth’s major plates on a world map, and
relate this pattern to the occurrence of earthquakes, volcanic
activity, and hot spots.

• Endogenic system encompasses internal
processes that produce flows of heat and material
from deep below Earth’s crust (Tectonics,
Earthquakes, and Volcanism). Radioactive
decay is the main energy source.
• Exogenic system involves external processes that
set into motion air, water, and ice, all powered by
solar energy (River, Landforms, Weathering,
Erosion, Oceans, Glaciers).
Two Broad Earth Systems

• Uniformitarianism is the guiding principle of
Earth Science.
– It is the assumption that the movements, systems and
cycles that occur today also operated in the past.
– The phrase “the present is the key to the past”
describes this principle.
– The principle applies to the process of gradual geologic
change, as well as sudden catastrophic events such as
earthquakes, volcanoes and asteroid impacts.
• The full scope of earths history can be
summarized using a timeline called the geologic
timescale
The Pace of Change

Relative Time and Superposition
• Principle of Superposition:
• Rock and sediment are always arranged with
the youngest bed “superposed” toward the top of
a rock formation and the oldest at the base, if
they have not been disturbed.
• a basic law of geochronology, stating that in any
undisturbed sequence of rocks deposited in
layers, the youngest layer is on top and the
oldest on bottom, each layer being younger than
the one beneath it and older than the one above
it.

The
Geologic
Time
Scale

The Geologic Time Scale
• Geologists organize the 4.6 billion years of earth's
history into sections based on important changes seen
in the geologic record.
• The largest intervals are eons, with each eon
composed of many millions of years.
• Within the eons are eras, which begin and end with
dramatic changes in the types of plants and animals
living on earth.
• Within each era are multiple periods, and within each
period are multiple shorter epochs.
• Therefore – eons – eras – periods - epochs

The Pace of Change
• The geologic time scale:
Eon>Era>Period>Epoch
Largest Smallest

• Because the intervals of the geologic timescale are
based on observed changes in fossilized remains on
life on earth, the span of time within each interval
varies
• While the divisions may be confusing at first, learning
about the events in earth's history goes hand-in-hand
with learning the geologic timescale.
• The geologic timescale is continually being revised by
new research and more accurate dating methods.

The Eons (From oldest to youngest):
• Hadean
• Archean
Proterozoic
• Phanerozoic (the Eon we are currently in)

The Eras (from oldest to youngest:
• Precambrian
• Paleozoic
• Mesozoic
• Cenozoic (the Era we are currently in)

The Periods from oldest to youngest:
• Cambrian
• Ordovician
• Solarium
• Devonian
• Mississippian
• Pennsylvanian
• Permian
• Triassic
• Jurassic
• Cretaceous
• Tertiary
• Quaternary (the period we are currently in)

How do you remember the order of the Periods?
Come------------------Cambrian
Over---------------------Ordovician
Some-------------------Solarium
Day----------------------Devonian
Maybe------------------Mississippian
Play---------------------Pennsylvanian
Poker-------------------Permian
This---------------------Triassic
Jerk---------------------Jurassic
Cheats-----------------Cretaceous
Then--------------------Tertiary
Quits--------------------Quaternary

The Epochs of the Cenozoic Era (from oldest to youngest:
• Paleocene,
• Eocene,
• Oligocene,
• Miocene,
• Pliocene,
• Pleistocene,
• Holocene (the Epoch we are currently in)

How do you remember the orders?
To memorize the Era:
Ø Precambrian, Paleozoic, Mesozoic, Cenozoic:
* Please pay my children!
*Pizza places make chicken.
*Peter Piper milks cows.
To memorize the Epochs of Cenozoic Era:
Ø Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene,
Holocene (or Recent):
* Pretty Eager Old Men Play Poker Hard.
* Pigeon Egg Omelets Make People Puke Heartily.
* Put Eggs On My Plate Please Homer.

So, we are currently living in:
The Phanerozoic Eon
The Cenozoic Era
The Quartenary Period
The Holocene Epoch
Is the Anthropocene the new epoch?A

• How old is the Solar System?
The Sun and its Solar System are
estimated to have occurred more than
4.6 billion years ago.
• How old is our Earth? How about the
Moon?
“Present thinking” places Earth’s age
at 4.6 billion years. The Moon is about
30 million years younger than Earth.
How Old is Our Earth?

• Two facts:
– The oldest rock on Earth is about
4.0 billion years old.
– The oldest fossil on Earth is about
3.5 billion years old.
How Do We Know the Age of Earth?

Radiometric Dating
Half-life, the decay-rate, is the time
required for one-half of the unstable
atoms in a rock sample to decay into
“daughter” isotopes.

Holocene
• Holocene is the youngest epoch in the
geologic time scale, characteristic of
postglacial conditions since the retreat
of the continental glaciers, about
11,500 years ago.

• Uniformitarianism is the guiding principle of Earth
Science.
• It is the assumption that the movements, systems and
cycles that occur today also operated in the past.
• The phrase “the present is the key to the past” describes
this principle.
• The principle applies to the process of gradual geologic
change, as well as sudden catastrophic events such as
earthquakes, volcanoes and asteroid impacts.
• The full scope of earths history can be summarized
using a timeline called the geologic timescale
Principle of Uniformitarianism

• Earth is thought to have condensed and
congealed from a nebula of dust, gas, and icy
comets about 4.6 billion years ago.
• Silica and iron are two dominant materials.
• During the early stages of the formation,
Earth’s temperature was so high that silica
and iron were all in liquid state.
• As temperature decreased, Earth solidified
and gravity sorted materials by density.
Formation of Earth

Earth’s Interior

Seismic Waves
• Scientists use seismic waves to probe Earth’s
internal structure and density profile.
• An earthquake or underground nuclear test sends
shock waves through the planet.
• Seismic waves travel at a higher speed in the
cooler and more rigid areas than in the hotter and
softer areas.
• The plastic zones do not transmit some seismic
waves, but absorb them.
• Density changes could induce reflection and
refraction of seismic waves.

Distances from Core to Crust

Earth’s Core
Earth’s core = inner core + outer core
Inner core is solid. (Why?)
Outer core is liquid.
Core mass = 1/3 of Earth’s mass.
Core volume = 1/6 of Earth’s volume.

• The fluid outer core generates 90% of
Earth’s magnetic field, because it is
made of liquid molten metallic iron.
• Migration of the north magnetic pole
(NMP), NMP now is at 85.1° N,
134° W.
• Magnetic poles and geographic poles are
different!
Earth’s Magnetism

• Average depth is about 2900 km.
• Two parts: lower mantle and upper mantle
• Consists of 80% Earth’s total volume
• Average density is 4.5g/cm3.
• The boundary between the uppermost
mantle and the crust above is called the
Mohorovicic discontinuity, or Moho.
Earth’s Mantle

The Asthenosphere and Lithosphere
• Between the upper mantle and the
uppermost mantle, there is a plastic-like layer
called the asthenosphere. A plastic layer will
slowly flow when a force is present. A rigid
layer will not flow when a force acts on it;
instead it will bend or break.
• Lithosphere consists of the crust and the
uppermost mantle.
• Average thickness of oceanic crust is 5 km,
and 30 km for continental crust.

• Buoyancy tells us that something less dense
(e.g., wood, ice) floats in something denser
(e.g., water).
• Earth’s crust floats on the denser layers
beneath, much as a boat floats on water.
• Where the load is greater (e.g., glaciers,
sediment, or mountains), the crust tends to sink,
or ride lower in the asthenosphere. Without that
load, the crust rides higher, in a recovery uplift
known as isostatic rebound.
• The entire crust is in a constant state of
compensating adjustment, or isostasy.
Buoyancy and Isostasy

Isostatic Adjustment
Isostatic (iso = “equal,”
static = “standstill”)
refers to the state of
gravitational
equilibrium between
the lithosphere and
asthenosphere such
that the tectonic plates
“float” at an elevation
that depends on their
thickness and density.

End of Chapter 12 PART 1
CLASS TEST ON THIS PART ON
1ST OCTOBER 2018

Geography ch12 part 1

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Geography ch12 part 1

Similar to Geography ch12 part 1 (20)

Recently uploaded

Recently uploaded (20)

Geography ch12 part 1