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Chapter 3 – Changing Climates

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  1. Pages 366 - 392 Chapter 3 – Changing Climates

  2. 3.1 – The Great Cooling (pages 368 – 374) • The Cenozoic Era extends back 65 million years • Cypress Hills interprovincial park contains sediments from the Cenozoic Era

  3. Rising Mountains • The Cenozoic Era in divided into 2 periods: • Tertiary Period: 65 – 1.7 million years ago • Quaternary Period: 1.7 million years ago – present

  4. North American and Pacific Plates collisions are at most intense at beginning of Cenozoic

  5. Plate activity also resulted in the northward migration of the North American Plate • North American climate got cooler • Climate was cool enough to form glaciers • Glaciers are responsible for carving out the familiar jagged features of the Rockies • Icy process began ~1.7 million years ago

  6. The Retreating Bearspaw Sea • During the late Cretaceous Period, much of southern Alberta was submerged under the Bearspaw Sea • Beginning of Cenozoic Era, the Bearspaw Sea had retreated to the southeast • Cenozoic sedimentary rock outcrops are evidence of rivers pouring sediment from the Rocky Mountains

  7. The Retreating Bearspaw Sea

  8. A Cooling Trend • There was a significant drop in average global temperatures during the first 15 million years of the Tertiary Period • Caused drastic changes to Alberta’s animal and plant life • Tropical forests became temperate evergreen forests

  9. ~2/3 of the way through the Tertiary Period Alberta was thought to resemble present day Louisiana

  10. Rise of the Mammals

  11. Rise of the Mammals • Surviving mammals at the end of the cretaceous period were mainly small rodents • By 40 million years ago, new forms of mammals appear in the fossil record • Ancestors of modern hooved herbivores • Flesh-eating carnivores • Large-brained primates

  12. Grasses, Grazers, and Big Predators • 35 million years ago, grasslands dominate Alberta’s landscape • Grasses are well suited for the cooler and drier climate • Grasslands became home to huge grazing herds and the predators that stalked them

  13. Evidence for a Cooling Trend • The overall cooling trend during the Tertiary Period was just one of many throughout Earth’s past • Evidence can be found in sedimentary rock • Absence of tree pollen in present-day tropical climates suggests that the past climate was much cooler • Presence of pollen in sedimentary rock of present-day polar regions suggests that climate was warmer in past

  14. 3.1 Summary • The end of the Mesozoic Era, 65 million years ago, saw the end of the Dinosaurs • Tectonic activity forms the Rocky Mountains and drains the Bearspaw Sea • An overall global cooling trend during the Tertiary Period resulted in a grassland Alberta that supported large herds of grazers and predators

  15. 3.2 – The Icy Epoch (pages 375 – 381)

  16. The Big Freeze • 1.7 million years ago, the climate became so cold that snow began to accumulate year after year in the polar regions • This marked the beginning of the Pleistocene Epoch • Layer upon layer of snow became compacted into sheets of ice (glaciers) • Glacier: a large river of ice that forms on land and moves under the influence of gravity

  17. When ice sheets reach a critical mass, they begin to slowly flow outward toward the equator like a viscous fluid • Earth’s current continental ice sheets cover nearly all of Antarctica and Greenland • When the edge of the glacier reaches the sea, huge chucks fall off in a process called “calving”

  18. Ice Age: a period during which ice sheets cover parts of the Northern and Southern Hemispheres • Glaciation: a period during which polar ice sheets advance to cover large regions of North America and northern Europe • Scientists believe that during the Pleistocene, there were at least four major glaciations

  19. Giants of the Pleistocene • During the chilly Pleistocene Epoch, large mammals had the advantage • Ie. wooly mammoths, wooly rhinoceros, modern horses, llamas, reindeer • Vicious predators stalked herds of large grazing mammals • Ie. American lions, short-faced bears, sabre-tooth cats

  20. 3.2 Summary • The cooling of the Tertiary Period reached a climax during the first part of the Quaternary Period – The Pleistocene Epoch • 4 major glaciation events occurred during the Pleistocene Epoch • Enormous sheets of ice continue to shape the world today

  21. 3.3 – Explaining and Predicting Climate Change (pages 382 – 389) • Weather: variables such as temperature, precipitation, and humidity is a certain place at a particular time • Climate: the average of daily and seasonal weather events that occur in a region over a long period of time (ie. 30 years)

  22. The Epoch of Recent Time - Holocene • The Holocene Epoch began ~10 000 years agoat the time of the great melt following the last glaciation • The rapid melting of glaciers opened ice free corridors that allowed individuals living in the North to migrate south

  23. Fluctuating Climate • Some changes in Earth’s climate seem to be chaotic in nature, while others seem to follow a pattern • Evidence contained in rock strata around the world suggests that during most of its history, Earth was warmer than it is today

  24. Possible Causes of Glaciation Periods • Interactions between Earth systems are very intricate, it is likely that glaciation periods are a result of the combination of the following effects: • Continents heading North • The ocean is a heat pump • Volcanic activity • Earth’s wobbly axis • Varying Sun intensity

  25. The Continents Heading North • Glaciation events seem to occur when large land masses are near the poles. • Continental ice sheets must form on land to cause glaciations • Forming ice sheets cause further cooling since they reflect much of the Sun’s solar energy; causing further cooling

  26. The Ocean is a Heat Pump • Oceans contain giant convection currents that transport heat around the globe • This has a warming effect on some areas of the world and a cooling effect on others • The warm circulating currents are known as the “global conveyor”.

  27. Volcanic Activity • Volcanoes are believed to be major contributors to past mass extinction events. • Volcanoes can also contribute to short-term fluctuations in climate • Mt. Pinatubo caused a drop in global average temperatures for at least 2 years

  28. Earth’s Wobbly Axis • Proposed by Milutin Milankovich • The amount of solar energy reaching the polar regions can be affected by: • The shape of Earth’s orbit • The tilt of Earth’s axis of rotation • The wobble of the axis of rotation

  29. Sun’s Changing Intenstiy • The Sun does not always shine with the same intensity • Intensity seems to follow a regular pattern determined by the pattern of sunspots. • During times of frequent sunspot activity, solar energy output is greater

  30. The Greenhouse Effect • Methane and carbon dioxide are naturally occurring greenhouse gases that trap heat near Earth’s surface • Without the greenhouse gases in our atmosphere, Earth would be much cooler • Volcanic eruptions, swamps and forest fires are all natural sources of greenhouse gases

  31. The Enhanced Greenhouse Effect • Human activities, such as the combustion of fossil fuels can increase the amount of greenhouse gases like carbon dioxide in the atmosphere • Many scientists believe that the sudden increase in the amount of carbon dioxide in the atmosphere during the last century has add a significant effect on the global average temperature

  32. 3.3 Summary • The Halocene Epoch (10 000 yrs ago – present) • Climate fluctuations in Earth’s past may have been due to a combination of factors: • Moving continents • Global conveyor • Volcanic activity • Wobbly axis • Fluctuating Sun intensity • Understanding climate change in the past can help us predict climate change into the future