Transcript REPLACE FIGURE - HCC Learning Web

Chapter 15
Cenozoic Events
The Cenozoic Era
• 65.5 million years ago to the present
• Name "Cenozoic" = "new life" or "recent
life"
• The Cenozoic Era followed a mass extinction of
the dinosaurs and many other organisms
• Cenozoic rocks contain modern types of plants
and animals, more advanced than those of
Paleozoic and Mesozoic.
• Cenozoic is the era of:
– Adaptive radiation of the mammals
– Cooling of the Earth's climate resulting in the
Ice Ages
– Evolution of humans
Periods of Cenozoic
• The Cenozoic Era consists of two periods:
– Younger Neogene Period
– Older Paleogene Period
• The Paris Basin is the type area for most
of the stages with Cenozoic. There is a
major unconformity in the basin that was
chosen as the boundary between
Cenozoic periods.
Periods of Cenozoic
• Until 2003, the two periods of Cenozoic were
Tertiary and Quaternary. You will see these
terms on older maps and in older publications.
• In 2003, the an international commission revised
the nomenclature, dropping the terms Tertiary
and Quaternary. The two new periods of the
Cenozoic are now internationally recognized as
Paleogene and Neogene.
Paleogene Period
Paleogene is divided into three epochs:
– Oligocene (youngest)
– Eocene
– Paleocene (oldest)
Neogene Period
Neogene is divided into four epochs:
– Holocene (the current epoch)
– Pleistocene
– Pliocene
– Miocene (oldest)
Cenozoic Time Chart
Naming the Epochs
• Some of the epochs were proposed by
Lyell in 1832 on the basis of proportions of
species of fossil marine invertebrates,
found in rocks of that time, that are still
living.
• For example, only 3% of Eocene
organisms found as fossils are still living,
whereas 17% of Miocene organisms found
as fossils are still alive, and 50-67% of
Pliocene fossils are still living.
Naming the Epochs
Pleist = most
The meanings of the
root words for the
epochs refer to the
proportions of fossil
species that are still
alive.
Pleion = more
Meion = less
Oligos = few
Eos = dawn
Paleo = ancient
Paleogeography and Plate
Tectonics
• During Cenozoic, the Atlantic and Indian
Oceans widened, and the continents
moved to their current positions.
• Half of the present ocean crust has formed
at the mid-ocean ridges since the
beginning of Cenozoic.
Position of the continents
during Eocene, about
50 m.y. ago.
Yellow = areas of major
tectonic changes.
Antarctica and Australia are still connected.
India has not yet collided with Asia.
North and South America are not yet connected.
South America is connected or nearly connected
with Antarctica.
Yellow = areas of major
tectonic changes.
Position of the continents today .
Antarctica has completely separated from
neighboring continents, and is surrounded by ocean.
Antarctica is centered on the South Pole.
Eocene vs. Today
Yellow = areas of major tectonic changes.
Exotic Terranes
As the North American
plate moved westward
(accompanying the
widening of the Atlantic
Ocean), subduction of
ocean crust and
accretion of exotic
terranes occurred
along its western edge.
San Andreas Fault System
• The western edge of the North American
plate came into contact with the
northwestward-moving Pacific Plate,
forming the San Andreas Fault system.
Closure of the Tethys Sea
•
Collision of Africa and India with Eurasia,
forming the Alps and Himalayas.
•
Tethys Sea deposits were deformed into
mountain ranges.
Tectonic and Paleographic Changes
and Their Effects on Climate
• Orogenic and volcanic activity were
intense along the western edge of the
North and South American plates.
• This caused the formation of the Isthmus
of Panama, a land bridge linking North and
South America.
• The land bridge provided a path for plant,
animal, and human migration between the
Americas.
Tectonic and Paleographic Changes
and Their Effects on Climate
• The Panama land bridge blocked the westward
flow of the North Atlantic Current. The current
was deflected to the north (turning to the right,
as a result of the Coriolis Effect), and formed the
Gulf Stream.
• The Gulf Stream transported warm water
northward and resulted in bringing warmer
climates to northwestern Europe.
• Gulf Stream also supplied warm, moist air
toward the North Pole, which would ultimately
result in precipitation which helped build the
glacial ice sheets.
Important continental breakups:
1. North Atlantic rift separated Greenland from
Scandinavia
2. Australia separated from Antarctica.
Circumpolar currents isolated Antarctica from
warmer waters. Led to cooling of Antarctica.
3. Cold, dense ocean waters around Antarctica
drifted northward along ocean floor,
contributing to global cooling and the Ice Age.
4. Rifting occurred between Africa and Arabia,
forming the Red Sea and the Gulf of Aden.
Tectonic and Paleographic Changes
and Their Effects on Climate
• Glaciation led to regressions.
• Continental interiors were not flooded by
epicontinental seas during Cenozoic.
• Marine transgressions were limited.
• Overall cooling trend during Cenozoic.
– Tropical and subtropical plants were replaced
by temperate plants, such as grasses.
– Tropical plants retreated toward the equator.
North America During Paleogene
Paleogene was dominated by:
– The deposition of marine sediments in
eastern and southeastern North America
– The presence of mountains and lakes in
western North America.
Paleogene
Period
Eastern and Southeastern
North America
• Ridges and valleys of the Appalachian
Mountains were carved by erosion. As
erosion proceeded, gentle isostatic uplift
occurred. This stimulated more erosion, as
streams cut downward.
Eastern and Southeastern
North America
Uplift in the eroding
Appalachians was coupled
with downward tilting and
deposition of sediments on
the Atlantic Coastal Plain
and continental shelf.
Sediments thicken seaward
forming a clastic wedge.
Eastern and Southeastern
North America
• Carbonate sediments accumulated in Florida
where less terrigenous clastic sediment was
available.
• Eight marine transgressions and regressions are
recorded in Cenozoic sediments on the Atlantic
and Gulf Coastal Plains.
• On the Gulf Coastal Plain, transgressions
brought Gulf of Mexico waters inland as far as
southern Illinois.
Eastern and Southeastern
North America
• During regressions, deltaic sands were
deposited over offshore shales in the Gulf of
Mexico region. These sediments provided ideal
conditions for formation and entrapment of oil
and gas. Much of the oil was trapped around salt
domes.
• A clastic wedge of sediments thickens seaward
in the Gulf of Mexico region, where Paleogene
sediments are >10,000 m (>5.5 mi) thick.
• Gulf of Mexico region has been subsiding
rapidly.
Rocky Mountains and
High Plains
• Structural features of the Cordillera were created
by Late Cretaceous and Paleogene deformation.
• Sediments eroded from the mountains were
trapped in low areas between the mountains, or
intermontane basins.
• Sediment from erosion of Rockies was spread
over the plains to the east. Oligocene through
Pliocene sands, shales, and lignites were
deposited on western high plains.
Rocky Mountains and
High Plains
• Beds of volcanic ash are interlayered with these
sediments, indicating volcanic activity, and
providing radiometric dates for correlation.
• Paleocene Fort Union Formation contains gray
sandstones and siltstones, carbonaceous
shales, lignites, and low sulfur coals, deposited
in swamps in the intermontane basins.
• These coals are used for electricity generation
and produce very little pollution because of the
low sulfur content.
Rocky Mountains and
High Plains
• Eocene Green River Formation is a lake
deposit with fossil fish, insects, plants,
varves, laminated oil shale, and limestone.
The Green River fish, Diplomystis
The Green River Formation, Utah
Rocky Mountains and
High Plains
• Late Eocene and Oligocene volcanic
activity in Yellowstone National Park area.
• White River Formation contains wellpreserved skeletons of Oligocene
mammals. Also makes up the Badlands of
South Dakota.
Rocky Mountains and
High Plains
• Well preserved fossil insects
and leaves are found at
Florissant Fossil Beds
National Monument in
Colorado. They were buried
when Oligocene volcanic ash
settled into a lake. Large
petrified stumps of sequoia
trees are also present.
Rocky Mountains and
High Plains
• Fluvial and lacustrine sedimentation
continued in intermontane basins and on
plains to east into the Miocene epoch.
• Climates had cooled by Miocene time.
• As the climate cooled, the grasslands
expanded and were populated by Miocene
camels, horses, rhinos, deer, and other
grazing mammals.
Rocky Mountains and
High Plains
• Volcanic activity occurred during Miocene in the
central and southern Rockies.
• Gold deposits at Cripple Creek, Colorado
formed in association with a Miocene volcano.
• Regional uplift of Rockies began in Miocene.
– Increased erosion rates.
– Sediment spread eastward, helping to build
the Great Plains.
Rocky Mountains and
High Plains
• Fossils in Pliocene sediments indicate
cooler and drier conditions.
• Normal faulting and volcanism
accompanied Cenozoic uplifts and
produced spectacular scenery.
Basin and Range Province
• The Basin and Range Province occupies a
broad area in Nevada and western Utah,
extending southward into Mexico.
• The province is dominated by up-faulted
mountain ranges and down-faulted basins.
Basin and Range Province
The Basin and Range formed as
follows:
1. The region was up-arched during
Mesozoic.
2. Subsidence occurred along normal faults
beginning during Miocene.
3. Up-faulted crustal blocks formed linear
mountains that shed sediment into the
adjacent down-dropped basins.
4. Faults opened conduits for igneous rock,
producing lava flows and volcanism.
5. Erosion followed the volcanism.
Sediments eroded from the mountains
filled the down-faulted basins, clogged
rivers, and caused closed-basin (no
outlet) lakes to form.
6. Evaporite minerals (gypsum and salt)
were deposited as the lakes evaporated.
Colorado Plateau Uplift
The Colorado
Plateau is centered
in the four-corners
region, where Utah,
Colorado, Arizona
and New Mexico
meet.
Colorado Plateau Uplift
The best-known feature in
the Colorado Plateau is
the Grand Canyon.
Eroded by the Colorado
River to a depth of more
than 1.6 miles.
The river eroded through
Phanerozoic strata and
into the Precambrian
basement rocks.
Colorado Plateau Uplift
• The rocks are relatively flat-lying. They were not
deformed during Mesozoic orogenies.
• The Colorado Plateau has been subject to uplift
and erosion. Uplift occurred during Pliocene.
• Faults formed locally, providing conduits for
volcanic rocks.
– Example: San Francisco Peaks near
Flagstaff, Arizona.
Columbia Plateau and
Cascade Range Volcanism
• Columbia Plateau is named for the Columbia
River, between Washington and Oregon.
• Columbia Plateau was built by volcanic activity.
• Basaltic lava poured out of deep fissures and
buried more than 500,000 km2 of land in
Washington, Oregon, and parts of Idaho during
Miocene, about 15 m.y. ago.
• Lava flows are more than 1.5 miles thick.
• One of the largest volcanic regions on Earth.
Columbia Plateau and
Cascade Range Volcanism
Left: Columbia Plateau basalts
in a canyon of the Snake River.
Right: Mt. St. Helens,
Washington, prior to eruption
and during eruption (1980).
Columbia Plateau and
Cascade Range Volcanism
• West of the Columbia
Plateau, more viscous
lava produced the
volcanoes of the Cascade
Range.
• Volcanism is caused by
the North American plate
overriding the Juan de
Fuca plate in the eastern
Pacific.
Volcanoes of the Cascade Range
•
•
•
•
•
•
•
•
Mt. St. Helens
Mt. Rainier
Mt. Adams
Mt. Hood
Mt. Jefferson
Mt. Lassen
Mt. Shasta
Others
Crater Lake
Crater Lake, Oregon formed from the
eruption and collapse of Mt. Mazama in
the Cascade Range about 6000 years
ago.
Origin of
Crater
Lake
Sierra Nevada Mountains
The Sierra Nevada
mountains lie to the
south of the Cascade
Range.
Sierra Nevada Batholith
The mountains belong
to a large granite body
called the Sierra
Nevada batholith.
The Sierra Nevada batholith formed as the
Farallon plate was being subducted under
the western edge of the North American
continental plate during Mesozoic.
Sierra Nevada Mountains
Erosion during Paleogene removed the
overlying rocks and caused the granite
batholith to be exposed at the surface.
Sierra Nevada Mountains
• During Pliocene and Pleistocene, the Sierra
Nevada batholith was raised up along
normal faults to a height of 4000 m (more
than 2 miles) above the California trough to
the west.
• Streams and glaciers carved the landscape.
• Examples – Yosemite, Lake Tahoe
California
• During Paleogene, the region west of the Sierra
Nevada was affected by subduction.
• During Miocene, strike-slip movement replaced
subduction.
• Faulting created islands and sedimentary basins.
• Marine clastic sediments, diatomites, and bedded
cherts were deposited in the basins.
• Folding and uplift led to regression.
New West Coast Tectonics
• During most of Cenozoic, subduction occurred
along the west coast.
• The Farallon plate was almost completely
subducted under North America.
• Only the small Juan de Fuca plate remains as a
corner of the once much larger Farallon plate.
• Part of the East Pacific rise spreading center
was subducted under North America.
New West Coast Tectonics
• Once the Pacific plate came into contact with the
North American plate, the direction of movement
changed.
• Instead of being subducted, the Pacific plate slid
laterally along the edge of the North American
plate.
• This formed the San Andreas fault with its
strike-slip motion, and ended subduction in this
area.
Around the World
• Active volcanism in many areas
– New Mexico, Arizona, Idaho
– Mexico
– Iceland
– Pacific rim
• Crustal uplift in many areas
– Tetons of Wyoming
– Sierra Nevada
– central and northern Rockies
– Alps
– Himalayas
Eocene vs. Today
Yellow = areas of major tectonic changes.
Closing of Tethys Sea and
Formation of Mountain Ranges
Basaltic lava flows in northern Europe and
neighboring areas as Greenland separated
from Europe
– Ireland - columnar basalts of Giant's Causeway
– Scotland
– Greenland
– Baffin Island
– Norway's Svalbard Islands
• Transgressions and regressions in the
Paris Basin area and formation of
evaporitic "Plaster of Paris" gypsum
deposits during Paleogene (Eocene to
Oligocene)
• Formation of rift valleys in East Africa,
along with associated lakes and volcanoes
• Separation of Australia from Antarctica
• Cooling and accumulation of snow and ice
in Antarctica
Cenozoic Paleoclimates
Global Surface Cooling
• There was a 10o C (18o F) temperature drop at
end of Cretaceous Period.
• Several warming trends occurred during late
Paleocene and Eocene, as indicated by:
– Fossils of palm trees and crocodiles in
Minnesota, Germany, and near London.
– Fossils of trees from temperate zones in
Alaska, Norway and Greenland.
– Coral reefs in latitudes 10-20o closer to the
poles than at present.
Antarctica during Paleogene
• The climate was semitropical and mild in
Antarctica during Paleogene, as indicated
by fossil spores and pollen, despite the
fact that it sat on the South Pole.
• Before Antarctica separated from
Australia, it was warmed by currents
moving southward from more equatorial
latitudes.
• Australia began to separate
from Antarctica during early
Eocene, about 55 m.y. ago.
• After separation, circumpolar
currents developed around
Antarctica, cutting it off from
equatorial currents.
• This resulted in temperature
decrease and glacial conditions
over Antarctica.
Yellow = areas of major
tectonic changes.
Global Surface Cooling
• Temperatures dropped by about 8-13o C
(roughly 22o F) near the Eocene-Oligocene
boundary, as indicated by isotope data from
brachiopods from New Zealand.
• Antarctic sea ice began to form by 38 m.y. ago.
• Greenhouse conditions were replaced by
icehouse conditions.
Worldwide cooling resulted in:
1. First Cenozoic widespread growth of glaciers in
Antarctica about 38-22 m.y. ago.
2. Global sea level dropped by about 50 m during
early Oligocene, as glaciers formed.
3. Cold, dense polar water flowed northward
across ocean bottom.
4. Upwelling of cold bottom waters affected world
climate.
5. Decrease in diversity and extinctions of many:
– marine molluscs
– planktonic and benthonic foraminifera
– ostracodes
6. Extinctions were earlier and more severe at
higher latitudes.
7. Reefs shifted toward the equator.
8. Calcarous biogenic deep sea sediments
(foraminiferal ooze) shifted toward the equator
and were replaced by siliceous biogenic
sediments (diatom and/or radiolarian ooze) at
higher latitudes.
9. Changes in pollen indicate long term cooling
and drying.
– Temperate and tropical forests shifted
toward the equator.
– Grasslands expanded.
– Rainforests became confined to tropical,
equatorial areas.
10. Glaciation occurred in other areas in Pliocene
(and younger) deposits - Sierra Nevada,
Iceland, South America, and Russia.
Mediterranean Evaporite Deposits
• Sea level drop, associated with glaciation during
Miocene, resulted in the isolation of the
Mediterranean basin.
• Deep canyons were cut by rivers feeding the
Mediterranean.
• The Mediterranean Sea dried up producing thick
(1000-2000 m) evaporite deposits (gypsum,
halite), 5-6 m.y. ago.
Antarctic Ice
• Antarctica has been covered by glaciers for at
least the past 15 m.y.
• The Antarctic ice sheet began to form during
Eocene.
• Glacial conditions established by Miocene
• East Antarctic ice cap present since middle
Miocene.
• During latest Miocene (about 5 m.y. ago), ice
volume in Antarctica was greater than today.
Antarctic Bottom Waters
• The cold waters around Antarctica were dense,
and sank to the ocean floor around Antarctica.
(Cold water is denser than warmer water.)
• Cold, dense ocean-floor waters moved
downward and outward, away from Antarctica.
• The northward movement of cold dense waters
contributed to cool conditions during late Eocene
and early Oligocene, and ultimately led to the
Pleistocene Ice Age.
Pleistocene
• Pleistocene began 1.8 m.y. ago.
• The most extensive glaciations began about
1 m.y. ago.
• The end of Pleistocene is when the ice sheets
melted to approximately their current extent.
• The Pleistocene-Holocene boundary is placed
between about 12,000 and 11,000 years ago, at
the midpoint of the warming of the oceans.
• This coincides with a rise in sea level.
Pleistocene Ice Age
• Pleistocene is significant as the time in which
humans evolved.
• More than 40 million km3 of snow and ice
covered about 1/3 of Earth's land area.
• Continental glaciers covered much of North
America and Europe.
• Alpine glaciers covered parts of the Cordilleran
Mountain range in western North America, the
Alps, and other mountain ranges of Europe.
Pleistocene continental glaciers in the Northern Hemisphere
As a result of the Ice Age:
1. Climatic zones in the Northern Hemisphere
were shifted southward.
2. Arctic conditions prevailed across Europe and
the U.S.
3. Sea level dropped as much as 75 m (225 ft)
and the shoreline shifted seaward, exposing
the continental shelves as dry land.
4. Streams cut deep canyons into the continental
shelves and on land.
5. Land bridges existed and led to migrations of
mammals, including humans
– Across the Bering Sea between Siberia and
Alaska
– Between Australia and Indonesia
– British Isles were attached to Europe
6. The land was sculpted by glaciers in Europe
and North America.
7. U-shaped valleys formed in mountainous
areas
8. Rainfall increased at lower latitudes.
9. Large lakes formed in the Basin and Range
Province.
– Lake Bonneville in Utah covered more than
50,000 km2 and was about 1000 ft deep in
places.
– The Great Salt Lake is a small remnant of
Pleistocene Lake Bonneville.
– The Bonneville salt flats were formed as the
lake evaporated.
10. Winds coming off glaciers blew sediment
southward forming löess deposits (Missouri
River area, central Europe, northern China)
11. Parts of northern and eastern Africa that are
currently arid had abundant water and were
fertile and populated by nomadic tribes.
12. Nomadic tribes hunted along the edges of the
continental glaciers. Wild game was abundant,
furs provided warm clothing, and there were
less problems with spoiled meat in the cold
temperatures.
13. Formation of the Great Lakes (depressions
scoured by glaciers and flanked by moraines)
14. Formation of Cape Cod, MA - a moraine
15. Formation of Long Island, NY - a terminal
moraine
16. Formation of Niagara Falls
17. Formation of large ice-dammed lakes,
including Lake Missoula which drained
catastrophically, forming the channeled
scablands
18. Formation of hummocky topography and
Pleistocene sand dunes
19. Weight of the ice
depressed the
continental crust to as
much as 200-300 m
downward.
20. Uplift (isostatic
rebound) after ice
melted. Coastal
features are now
elevated high above
sea level.
Map illustrating postglacial uplift in North
America.
Advance of the Ice Sheets
• Late Pliocene and Pleistocene had strong, rapid,
climatic fluctuations.
• Ice ages are characterized by glacial expansions
separated by warmer interglacial intervals.
• Before the mid-1970's, Pleistocene was divided
into four glacial stages with intervening warmer
interglacial stages.
• More recent investigations have shown that
there may have been as many as 30 glacial
advances over the past 3 million years (roughly
every 100,000 years.)
Names of the "traditional" glacial and interglacial
stages in North America
Stratigraphy of Pleistocene
Deposits
Pleistocene deposits are difficult to date
and correlate.
Pleistocene sedimentary deposits,
however, may show evidence of
fluctuating climatic conditions, which can
be used to mark times of glacial advance
and retreat.
1. Evidence of glacial conditions
• Glacial till - unsorted mixture of clay to bouldersized particles.
Amount of weathering of glacial deposits or
soils, and the amount of dissection by streams
may help with relative dating.
• Bedrock with glacial striations
• Stratified drift - glacial deposits which have been
washed and sorted by meltwater
• Varved clays - seasonal laminations deposited
in glacial lakes. Counting varves may reveal the
number of years during which they clay was
deposited.
2. Plant remains
• Pollen grains - types of plants indicate
climate
• Fossil angiosperm leaf shapes indicate
climate
Smooth margin = WARM climate
Jagged margin = COOL climate
3. Radiometric dating of wood, bone, or peat
using carbon-14.
– For materials less than 100,000 years old due
to the short half-life of carbon-14 (5730 yrs).
– Only useful for the most recent glacial stage.
4. Magnetic stratigraphy
The record of magnetic reversals in cores of deep
sea sediments can be correlated to magnetic
reversals in volcanic rocks.
– Volcanic rocks can be dated radiometrically,
and the dates applied to the sediments with the
same magnetic characteristics.
5. Correlation of deep-sea sediments
from cores, using fossil remains,
particularly microfossils such as
foraminifera. Fossils can be dated by
relating them to paleomagnetic data and
to radiometric dates.
6. Oxygen isotope ratios
• Ratio of O-18 to O-16 in foram shells from cores
tells us the volume of water stored in glacial ice.
• Numbers 16 and 18 refer to atomic mass or total
number of protons and neutrons in the O atom.
• Atomic number of O is 8 (O has 8 protons).
– Oxygen-16 has 8 neutrons, and
– Oxygen-18 has 10 neutrons.
• An atom of oxygen with 10 neutrons is heaver
than an atom of oxygen with 8 neutrons.
6. Oxygen isotope ratios – cont’d
• Oxygen is present in water (H2O) and in some
minerals, such as calcite or aragonite (CaCO3),
that make up the shells of forams.
• Ratio of O-18 to O-16 in the water (and in shells)
depends on temperature.
• Lighter oxygen isotopes (O-16) accumulate in
glacial ice. Why? During evaporation, lighter
isotopes are concentrated in the water vapor in
the air. Water with lighter oxygen (O-16) is
easier to evaporate than water with heavier
oxygen (O-18).
6. Oxygen isotope ratios – cont’d
• Water vapor condenses and falls as rain or
snow. Snow may accumulate to form glaciers.
As a result, O-16 becomes trapped in glacial ice.
• O-18 remains in the oceans, because water with
O-18 did not evaporate as readily.
• As temperatures drop, air becomes drier, and
the percentage of O-18 in seawater (and in
foram shells) increases.
6. Oxygen isotope ratios – cont’d
• Foraminifera and the oxygen-16/18 signal:
• Foram shells rich in O-18 = COLD & DRY, or
glacial conditions.
• Foram shells rich in O-16 = WARM & WET, or
interglacial conditions.
Graph representing
variations in the oxygen
isotope ratios in foram
shells (and in the global
volume of ice) over the
past 500,000 years.
7. The type of foraminifera fossil
present may indicate something
about the paleoclimate.
Some species live in warmer water. If
those species are absent, it may indicate
that the water was colder due to a
glaciation.
8. Coiling directions in foraminifera shells
One particular species of foraminifera,
Globorotalia truncatulinoides, is known to coil:
– to the right in warmer waters, and
– to the left in colder waters.
By examining the percentage of right- and leftcoiled specimens, a cyclic pattern
representing glacial advances and retreats
can be determined.
Graphs illustrating the
percentages of right-coiling
and left-coiling foraminifera,
Globorotalia truncatulinoides.
The vertical scale is depth in
deep sea sediment cores, in
centimeters.
Why Did Earth's Surface Cool?
There was both a long-term decline in
temperatures, as well as an oscillation of
glacial and interglacial stages.
Any hypothesis for the cooling must
consider both of these factors.
Milankovitch Cycles
• A widely accepted hypothesis for the
temperature fluctuations is related to
Earth's orbital oscillations.
• This hypothesis was developed by
Yugoslavian mathemetician Milutin
Milankovitch, and it is referred to as the
Milankovitch cycles.
Milankovitch Cycles
• The cyclic climatic changes result from
changes in the distance and angular
relationships between the Earth and Sun
due to periodic fluctuations in Earth's orbit.
Milankovitch Cycles
1. Precession - Earth's axis wobbles or moves in a
circle like a spinning top over 26,000 years,
affecting the amount of solar radiation received
at the poles.
Milankovitch Cycles
2. Orbital eccentricity - Earth's orbit around the Sun
changes from more circular to more elliptical by
about 2% over about 100,000 years, moving the
Earth closer to or farther from the Sun, and
varying the amount of solar radiation received by
the Earth.
Milankovitch Cycles
3. Angle of tilt of Earth's axis currently about 23.5o, this
tilt angle causes the
seasons.
Tilt angle varies from about
21.5o - 24.5o over about
41,000 years, changing
length of days and amount
of solar radiation received
at the poles.
Milankovitch Cycles
• The combination of these variables periodically
results in a change in the amount of solar
radiation received by the Earth, which causes
cycles of cooling and periodic glaciations.
• Milankovitch cycles correspond well to glaciation
episodes, which have occurred every 100,000
years over the past 600,000 years, as indicated
by oxygen isotope data.
Non-Milankovitch Factors in
Global Climate Change
1. Albedo or reflectivity of the Earth
If Earth's albedo increased, due to snow cover,
cloud cover, or dust in the atmosphere, the
atmospheric temperatures would decrease due to
reflection of solar radiation into space.
As snow cover increased, albedo would increase,
producing a positive feedback relationship,
accelerating the rate of glacial growth.
A 1% loss of incoming solar energy would result
in a temperature drop of about 8o C, which might
be sufficient to trigger glacial buildup.
2. A decrease in atmospheric CO2 would cause a
decrease in the greenhouse effect, and lead to
cooling.
3. Conversely, an increase in atmospheric CO2
would cause warming, which would result in
more rapid evaporation, more cloud cover, and
an increase in albedo, which could trigger
glaciation.
4. Plate tectonics is important in that a continent
must lie on or near a pole for snow to build up
to form a glacier.
5. Plate tectonics is further involved because the
formation of the Isthmus of Panama diverted
the Gulf Stream northward about 3.5 million
years ago. The warm, moist air associated with
this ocean current led to an increase in snowfall
in northern areas and the development of
continental glaciers.
6. The impact of human activities, such as
increased burning of fossil fuels and the
associated buildup of greenhouse, is having and
will continue to have an effect.
The "Little Ice Age"
• Cold spells recurred periodically into Holocene.
• The "Little Ice Age" lasted from 1540 – 1890.
Temperatures were several degrees cooler than
today.
• Loss of harvests, famine, food riots, and warfare
in Europe.
• Cold conditions correlate with periods of low
sunspot activity.
• A time of extremely low sunspot activity from
1645 -1715 is known as the Maunder Minimum.
The "Little Ice Age" – cont’d
• Heightened volcanic activity occurred
during the Little Ice Age.
• Volcanic ash and aerosols in the
atmosphere caused temperatures to drop
by blocking out incoming solar radiation.
• The eruption of Mount Tambora in
Indonesia in 1815 was followed by the
"Year Without A Summer."
• Frost and snow were reported during June
and July of 1816 in New England and
End of the "Little Ice Age"
• Human-induced warming may be the
reason for the end of the "Little Ice Age."
• Greenhouse gases associated with the
Industrial Revolution are the major factors
influencing global warming and climate
change today.