1 Chapter 15 Cenozoic Events REPLACE FIGURE (Chapter cover art)

2 The Cenozoic Era 65.5 million years ago to the presentName "Cenozoic" = "new life" or "recent life"

3 The Cenozoic Era followed a mass extinction of the dinosaurs and many other organismsCenozoic 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

4 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.

5 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.

6 Paleogene Period Paleogene is divided into three epochs: EoceneOligocene (youngest) Eocene Paleocene (oldest)

7 Neogene Period Neogene is divided into four epochs: PleistoceneHolocene (the current epoch) Pleistocene Pliocene Miocene (oldest)

8 Cenozoic Time Chart REPLACE FIGURE (Part of Table 15-1)

9 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.

10 Naming the Epochs Pleist = most Pleion = more Meion = less Oligos = few Eos = dawn Paleo = ancient The meanings of the root words for the epochs refer to the proportions of fossil species that are still alive.

11 Paleogeography and Plate TectonicsDuring 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.

12 during Eocene, about 50 m.y. ago.Position of the continents during Eocene, about 50 m.y. ago. 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. REPLACE FIGURE (Fig. 15-1a) Yellow = areas of major tectonic changes.

13 Antarctica is centered on the South Pole.REPLACE FIGURE (Fig. 15-1b) 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.

14 Eocene vs. Today Yellow = areas of major tectonic changes.REPLACE FIGURE (Fig. 15-1) Yellow = areas of major tectonic changes.

15 Exotic Terranes REPLACE FIGURE (Fig. 7-65) 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.

16 San Andreas Fault SystemThe western edge of the North American plate came into contact with the northwestward-moving Pacific Plate, forming the San Andreas Fault system.

17 Closure of the Tethys SeaCollision of Africa and India with Eurasia, forming the Alps and Himalayas. Tethys Sea deposits were deformed into mountain ranges.

18 Tectonic and Paleographic Changes and Their Effects on ClimateOrogenic 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.

19 Tectonic and Paleographic Changes and Their Effects on ClimateThe 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.

20 Important continental breakups:North Atlantic rift separated Greenland from Scandinavia Australia separated from Antarctica. Circumpolar currents isolated Antarctica from warmer waters. Led to cooling of Antarctica. Cold, dense ocean waters around Antarctica drifted northward along ocean floor, contributing to global cooling and the Ice Age. Rifting occurred between Africa and Arabia, forming the Red Sea and the Gulf of Aden.

21 Tectonic and Paleographic Changes and Their Effects on ClimateGlaciation 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.

22 North America During PaleogenePaleogene was dominated by: The deposition of marine sediments in eastern and southeastern North America The presence of mountains and lakes in western North America.

23 Paleogene Period REPLACE FIGURE (Fig. 15-7)

24 Eastern and Southeastern North AmericaRidges 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.

25 Eastern and Southeastern North AmericaUplift 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. REPLACE FIGURE (Fig. 15-4)

26 Eastern and Southeastern North AmericaCarbonate 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.

27 Eastern and Southeastern North AmericaDuring 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.

28 Rocky Mountains and High PlainsStructural 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.

29 Rocky Mountains and High PlainsBeds 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.

30 Rocky Mountains and High PlainsEocene Green River Formation is a lake deposit with fossil fish, insects, plants, varves, laminated oil shale, and limestone. REPLACE FIGURE (Fig ) REPLACE FIGURE (Fig ) The Green River fish, Diplomystis The Green River Formation, Utah

31 Rocky Mountains and High PlainsLate Eocene and Oligocene volcanic activity in Yellowstone National Park area. White River Formation contains well-preserved skeletons of Oligocene mammals. Also makes up the Badlands of South Dakota.

32 Rocky Mountains and High PlainsWell 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. REPLACE FIGURE (Part of Fig )

33 Rocky Mountains and High PlainsFluvial 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.

34 Rocky Mountains and High PlainsVolcanic 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.

35 Rocky Mountains and High PlainsFossils in Pliocene sediments indicate cooler and drier conditions. Normal faulting and volcanism accompanied Cenozoic uplifts and produced spectacular scenery.

36 Basin and Range ProvinceThe 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.

37 Basin and Range ProvinceREPLACE FIGURE (Fig )

38 The Basin and Range formed as follows:The region was up-arched during Mesozoic. Subsidence occurred along normal faults beginning during Miocene. Up-faulted crustal blocks formed linear mountains that shed sediment into the adjacent down-dropped basins.

39 Faults opened conduits for igneous rock, producing lava flows and volcanism.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. Evaporite minerals (gypsum and salt) were deposited as the lakes evaporated.

40 Colorado Plateau UpliftREPLACE FIGURE (Fig ) The Colorado Plateau is centered in the four-corners region, where Utah, Colorado, Arizona and New Mexico meet.

41 Colorado Plateau UpliftREPLACE FIGURE (Fig ) 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.

42 Colorado Plateau UpliftThe 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.

43 Columbia Plateau and Cascade Range VolcanismColumbia 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.

44 Columbia Plateau and Cascade Range VolcanismREPLACE FIGURE (Fig ) REPLACE FIGURE (Fig ) Left: Columbia Plateau basalts in a canyon of the Snake River. Right: Mt. St. Helens, Washington, prior to eruption and during eruption (1980).

45 Columbia Plateau and Cascade Range VolcanismWest 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. REPLACE FIGURE (Fig )

46 Volcanoes of the Cascade RangeMt. St. Helens Mt. Rainier Mt. Adams Mt. Hood Mt. Jefferson Mt. Lassen Mt. Shasta Others

47 Crater Lake Crater Lake, Oregon formed from the eruption and collapse of Mt. Mazama in the Cascade Range about 6000 years ago. REPLACE FIGURE (Fig )

48 Origin of Crater Lake REPLACE FIGURE (Fig )

49 Sierra Nevada MountainsREPLACE FIGURE (Fig ) The Sierra Nevada mountains lie to the south of the Cascade Range.

50 Sierra Nevada BatholithREPLACE FIGURE (Fig ) The mountains belong to a large granite body called the Sierra Nevada batholith.

51 REPLACE FIGURE (Fig ) The Sierra Nevada batholith formed as the Farallon plate was being subducted under the western edge of the North American continental plate during Mesozoic.

52 Sierra Nevada MountainsErosion during Paleogene removed the overlying rocks and caused the granite batholith to be exposed at the surface. REPLACE FIGURE (Part of Fig )

53 Sierra Nevada MountainsDuring 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

54 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.

55 New West Coast TectonicsDuring 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.

56 New West Coast TectonicsOnce 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.

57 Around the World Active volcanism in many areasNew Mexico, Arizona, Idaho Mexico Iceland Pacific rim Crustal uplift in many areas Tetons of Wyoming Sierra Nevada central and northern Rockies Alps Himalayas

58 Eocene vs. Today Yellow = areas of major tectonic changes.REPLACE FIGURE (Fig. 15-1) Yellow = areas of major tectonic changes.

59 Closing of Tethys Sea and Formation of Mountain RangesREPLACE FIGURE (Fig )

60 Basaltic lava flows in northern Europe and neighboring areas as Greenland separated from EuropeIreland - columnar basalts of Giant's Causeway Scotland Greenland Baffin Island Norway's Svalbard Islands

61 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

62 Cenozoic Paleoclimates

63 Global Surface CoolingThere 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.

64 Antarctica during PaleogeneThe 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.

65 REPLACE FIGURE (Fig. 15-1) 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.

66 Global Surface CoolingTemperatures 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.

67 Worldwide cooling resulted in:First Cenozoic widespread growth of glaciers in Antarctica about m.y. ago. Global sea level dropped by about 50 m during early Oligocene, as glaciers formed. Cold, dense polar water flowed northward across ocean bottom. Upwelling of cold bottom waters affected world climate.

68 Decrease in diversity and extinctions of many:marine molluscs planktonic and benthonic foraminifera ostracodes Extinctions were earlier and more severe at higher latitudes. Reefs shifted toward the equator. 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.

69 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. Glaciation occurred in other areas in Pliocene (and younger) deposits - Sierra Nevada, Iceland, South America, and Russia.

70 Mediterranean Evaporite DepositsSea 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 ( m) evaporite deposits (gypsum, halite), 5-6 m.y. ago.

71 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.

72 Antarctic Bottom WatersThe 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.

73 Pleistocene Pleistocene began 1.8 m.y. ago.The most extensive glaciations began about 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.

74 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.

75 Pleistocene continental glaciers in the Northern HemisphereREPLACE FIGURE (Fig ) Pleistocene continental glaciers in the Northern Hemisphere

76 As a result of the Ice Age:Climatic zones in the Northern Hemisphere were shifted southward. Arctic conditions prevailed across Europe and the U.S. Sea level dropped as much as 75 m (225 ft) and the shoreline shifted seaward, exposing the continental shelves as dry land. Streams cut deep canyons into the continental shelves and on land.

77 Land bridges existed and led to migrations of mammals, including humansAcross the Bering Sea between Siberia and Alaska Between Australia and Indonesia British Isles were attached to Europe The land was sculpted by glaciers in Europe and North America. U-shaped valleys formed in mountainous areas

78 Rainfall increased at lower latitudes.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.

79 Winds coming off glaciers blew sediment southward forming löess deposits (Missouri River area, central Europe, northern China) Parts of northern and eastern Africa that are currently arid had abundant water and were fertile and populated by nomadic tribes. 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.

80 Formation of the Great Lakes (depressions scoured by glaciers and flanked by moraines)Formation of Cape Cod, MA - a moraine Formation of Long Island, NY - a terminal moraine Formation of Niagara Falls Formation of large ice-dammed lakes, including Lake Missoula which drained catastrophically, forming the channeled scablands Formation of hummocky topography and Pleistocene sand dunes

81 REPLACE FIGURE (Fig ) Weight of the ice depressed the continental crust to as much as m downward. Uplift (isostatic rebound) after ice melted. Coastal features are now elevated high above sea level. Map illustrating post-glacial uplift in North America.

82 Advance of the Ice SheetsLate 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.)

83 Names of the "traditional" glacial and interglacial stages in North AmericaREPLACE FIGURE (Table 15-2)

84 Stratigraphy of Pleistocene DepositsPleistocene 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.

85 1. Evidence of glacial conditionsGlacial till - unsorted mixture of clay to boulder-sized 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.

86 2. Plant remains Pollen grains - types of plants indicate climateFossil angiosperm leaf shapes indicate climate     Smooth margin = WARM climate     Jagged margin = COOL climate

87 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.

88 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. REPLACE FIGURE (Fig )

89 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.

90 6. Oxygen isotope ratios – cont’dOxygen 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).

91 6. Oxygen isotope ratios – cont’dWater 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.

92 6. Oxygen isotope ratios – cont’dForaminifera 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. REPLACE FIGURE (Fig )

93 Graph representing variations in the oxygen isotope ratios in foram shells (and in the global volume of ice) over the past 500,000 years. REPLACE FIGURE (Fig )

94 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.

95 8. Coiling directions in foraminifera shellsOne 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 left-coiled specimens, a cyclic pattern representing glacial advances and retreats can be determined.

96 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. REPLACE FIGURE (Fig )

97 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.

98 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.

99 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.

100 Milankovitch Cycles 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. REPLACE FIGURE (Fig a)

101 Milankovitch Cycles REPLACE FIGURE (Fig b) 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.

102 Milankovitch Cycles REPLACE FIGURE (Fig c) Angle of tilt of Earth's axis - currently about 23.5o, this tilt angle causes the seasons. Tilt angle varies from about 21.5o o over about 41,000 years, changing length of days and amount of solar radiation received at the poles.

103 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.

104 Non-Milankovitch Factors in Global Climate ChangeAlbedo 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.

105 A decrease in atmospheric CO2 would cause a decrease in the greenhouse effect, and lead to cooling.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.

106 Plate tectonics is important in that a continent must lie on or near a pole for snow to build up to form a glacier. 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.

107 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. REPLACE FIGURE (Fig )

108 The "Little Ice Age" Cold spells recurred periodically into Holocene.The "Little Ice Age" lasted from 1540 – 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 is known as the Maunder Minimum.

109 The "Little Ice Age" – cont’dHeightened 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 Northern Europe.

110 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.