Transcript powerpoint

The Life
of Rocks
James Hutton
(1726-1797)
“No vestige of a
beginning, no
concept of an end.”
Types of Rocks
Basalt
Sandstone
Granite
Igneous
Limestone
Sedimentary
Marble
Slate
Metamorphic
Extrusive Igneous Rocks
Igneous rocks are
formed by the
cooling and
crystalization of hot,
molten rock called
magma. The word
igneous means
“formed by fire.”
Igneous rocks make
up about 95% of the
Earth’s crust. Basalt
and granite are
common igneous
rocks
Conceptual Physical
Science
Hewitt, Suchocki, Hewitt
Extrusive Igneous rocks are created from magma
that cools on the surface of the Earth, such as this
basalt being formed from a lava flow in Hawaii.
Sunset Crater, Flagstaff AZ
This field of basalt, and extrusive igneous rock, is about 1000 years old.
Intrusive Igneous Rocks
The Navajo word for Shiprock is Tse'Bit'Ai, and means "rock with
wings." Shiprock was formed by a volcanic vent 27 million years
ago. At that time the surrounding land was 2000 feet higher. When
the column of lava cooled, the softer earth eroded and left a 1700
foot stone pillar atop a 5500 plain. The wings are three lava walls 150
feet high and three feet wide. Shiprock is the world's finest example
of an exposed volcanic throat and can be seen for 100 miles.
Intrusive Igneous: Granite
Granite is a common type of intrusive igneous rock. It is formed far below
the surface of the Earth at high pressure and temperature and as a
consequence is more dense than basalt.
Classification of Igneous Rocks
Sedimentary Rocks: Sandstone
A wall of
Coconino
sandstone in
the Grand
Canyon
Sandstone is a sedimentary rock formed from sand in ancient beaches, deserts,
or sea beds. Sandstone is composed primarily of quartz. If you examine
sandstone carefully you can see the individual sand grains from ancient terrains.
Sedimentary Rocks: Limestone
Limestone is composed mostly of calcium carbonate (CaCO3). It is created from
skeletons and shells that accumulated on the floor of ancient sea beds or from
ancient corral reefs. Limestone deposits commonly contain fossils of ancient sea
life.
Metamorphic Rocks
A marble
outcrop in
Vermont is
shown to the
left.
Other types of
metamorphic
rocks include
schists,
gneisses, and
quartzsite.
Marble is a metamorphic rock that originally began as limestone. Continuing
sedimentary processes buried the limestone under layers of shale, sand, and
other limestone. Movements on the Earth’s crust caused great pressures and
temperatures that converted the limestone to marble. Eventually, the marble was
returned to the Earth’s surface, where it is mined by humans.
The Surface of the Earth:
Erosion & sedimentary rocks
What more can we require?
Nothing but time.
James Hutton, defining
uniformitarianism (vs catastrophism)
Review of 3 Rock Types
The surface of the Earth is
made of mostly sedimentary
rock while the crust (surface
and layers below) is made of
mostly igneous rock.
Erosion of Igneous Rocks
This photo shows a thunder storm over Yosemite valley in
Sierra Nevada mountain range. The Sierra Nevada are
made mostly of granite. Rain accompanies the thunder
and lightning and has a more lasting impact on the
mountains.
The water flows downstream
As this waterfall in
Yosemite shows, water
from rain and snow melt
flows to lower altitudes
taking with it some
dissolved minerals and
small pieces of rocks and
debris.
The Sediment is Deposited
The Colorado River is the main
drainage for the southwestern
United States. The material
carried along by the flowing
waters in eventually deposited in
the ocean and the Colorado river
delta in Baja, Mexico.
Today, essentially all of the
Colorado river is used for
irrigation in support of cities in the
southwestern USA. Very little
water makes it south of the border
to Mexico and the delta is dry
compared with its former state.
Herodotus & the Nile
A satellite view of the Nile
delta. The brownish/green
areas are sediment.
Herodotus (~450 BC) in the Histories mentions that fossils of sea life can be
found hundreds of stade inland along the Nile river in Egypt. He reasoned
correctly that the silt deposited by the river must be extending the reach of land
and inferred that Egypt was created by this process. It was 2500 years before
his suggestion was taken seriously.
Old and Young Mountains
The Rocky Mountains (right) are 65
million years old while the Smoky
Mountains (above) are 400 million
years old. Because of erosion the
Smokies are rounded with gentle
slopes, while the Rockies have sharp
edges and steep slopes.
Lifetime of a Mountain
All mountains have streams. Let’s assume that the average stream carries a
cubic volume of 0.1 m3 of sediment off the mountain each day. Let’s also
assume that the average mountain has 4 streams. The sediment removed each
year is then
Erosion Rate=4 streams x 0.1 m3/stream-day x 365 days/year = 146 m3/year
How big is the average mountain? There is no average mountain, but typical
dimensions might be 2 km high by 4 km wide and 4 km long (1.2 mi x 2.5 mi x
2.5 mi). The volume is
Volume = 2 km x 4 km x 4 km = 32 km3 = 3.2x1010 m3
The lifetime of the mountain is the volume divided by the erosion rate or,
Lifetime = 3.2x1010 m3 / 146 m3/year = 2.13x108 years = 213 million years
Although this seems like a long time, it is short compared with the lifetime of the
Earth (4.5 billion years). Thus, mountain ranges formed when the Earth was
young must be long gone. It follows that mountains must be continually formed.
The Age of Earth
James Ussher, Archbishop of Ireland (1581-1656):
Earth was created on Saturday evening, October
22, 4004 BC
James Hutton: The Earth is much older than that as
witnessed by presence of thick layers of
sedimentary rock.
Erosion in the Ice Age
20,000 years ago the Earth
experienced a relatively cool
period known as an ice age.
During this time the polar ice
sheets extended to much lower
latitudes than they do now and
glaciers cover the northern
parts of the American,
European, and Asian
continents.
A flowing glacier is a particularly
powerful agent for erosion.
Glaciers
Rivers Make V-Shaped Valleys
This photograph shows how
the Yellowstone river carves
out the V-shaped Yellowstone
valley. The valley comes to a
point at the bottom that is as
wide as the river itself.
U-Shaped Valley
Some valleys
are U-shaped
with a wide flat
bottom, much
broader than
the width of the
river.
The U-shaped
valleys have
been carved by
glaciers.
Hanging Valleys
Bridal Veil falls (left) marks the location of a hanging
valley, a common feature in glacially carved valleys.
Glacial Moraines
When a glacier retreats (melts) it leaves behind a pile of debris formerly held
in the ice. These debris piles are called moraines.
Some Famous Glacial Moraines
Cape Cod
Long Island
Cape Cod and Long Island mark the southern most extent of the ice cap
during the ice age.
Erosion of Sedimentary Rocks
Sedimentary rocks tend to be soft and are quickly eroded. The effects of
flowing water can be clearly seen in the photograph of Zion national park.
Stratigraphy
Principle of original horizontally. Sediments are deposited as horizontal beds.
Principle of superposition. Younger layers lie on top of older layers.
Principle of Uniformity
• physical and chemical laws are invariant with time,
• geomorphic processes are of the same kind and rate as in the
past, and thus
• the history of the earth can be explained from current
observations and relationships.
The History of the Earth can
be read in Strata
Thousands of years
Geological Time
Bryce Canyon