5. Extent and Causes of Glaciation:
• Glacial events often associated with the
positioning of large landmasses over or near the
poles.
• Many glaciation events throughout the
Phanerozoic
6. Extent and Causes of Glaciation:
• several occurred
during the
Pleistocene
• > massive continental
ice sheets
• > often 2 to 3 km thick
• > at maximum, 1/3 of
earth’s land mass
7. Extent and Causes of Glaciation:
• > during glacial maxima
• 1) unglaciated temperate regions were
cooler and wetter than those of today
=> referred to as Glacio-pluvial (ice-rain)
periods in now arid areas
• 2) Tropical regions tended to be drier
during glacial maxima
8. Extent and Causes of Glaciation:
• > during glacial maxima
• 1) unglaciated temperate regions were
cooler and wetter than those of today
=> referred to as Glacio-pluvial (ice-rain)
periods in now arid areas
• 2) Tropical regions tended to be drier
during glacial maxima
9. Extent and Causes of Glaciation:
• most recent glacial period,
• ice sheets in the Northern Hemisphere
covered to the 45 o latitude
• North America and Central Asia
• 80% of ice sheets during Pleistocene
occurred in Northern Hemisphere
10. Extent and Causes of Glaciation:
• > in Southern Hemisphere (except for
Antarctica), glaciation was mostly confined
to high latitudes
11. Milankovitch Cycles
• Changes in interception and absorption of
solar radiation by the earth’s surface
resulted from changes in its orbit =>
Milankovitch Cycles
12. Milankovitch Cycles
• Changes in interception and absorption of
solar radiation by the earth’s surface
resulted from changes in its orbit =>
Milankovitch Cycles
• 1) Earth’s orbit varies in ellipticity with a
period of 100,000 years
13. Milankovitch Cycles
• Changes in interception and absorption of
solar radiation by the earth’s surface
resulted from changes in its orbit =>
Milankovitch Cycles
• 1) Earth’s orbit varies in ellipticity with a
period of 100,000 years
• 2) Tilt of the earth (obliquity) varies from
22.1 to 24.5 o with a 41,000 year period
14. Milankovitch Cycles
• 3) Earth’s orientation or Precession
wanders with the axis of the North Pole
shifting from one “North Star” (presently
Polaris of Ursa Minor) to another (Vega of
Lyra) with a periodicity of 22,000 years
15. Milankovitch Cycles
• > combined effects result in significant
changes in the amount of solar energy
striking the earth
16. Glacial and Interglacial Periods
• Transitions between glacial and
interglacial periods were influenced by
remarkable feedback effects
17. Glacial and Interglacial Periods
• Transitions between glacial and
interglacial periods were influenced by
remarkable feedback effects
• 1) Initial stages of glaciation resulted in
increased reflectance (from snow and ice)
over large parts of the earth -> reduced
effective solar heating and further
increased cooling rate
18. Glacial and Interglacial Periods
• Transitions between glacial and interglacial
periods were influenced by remarkable feedback
effects
• 1) Intial stages of glaciation resulted in
increased reflectance (from snow and ice) over
large parts of the earth -> reduced effective solar
heating and further increased cooling rate
• 2) Deglaciation was increased by buildup of
greenhouse gases (carbon dioxide and
methane)
19. Effects on Nonglaciated Areas:
• Latitudinal gradients were much less
pronounced during most of the
Phanerozoic
20. Effects on Nonglaciated Areas:
• In the Miocene, global climates began to
cool and become drier
• > oceanic and atmospheric circulation
during the mid-Miocene (15 million years
B.P.) established a strong latitudinal
thermal gradient that intensified during
interglacial periods
21. Effects on Nonglaciated Areas:
• > average air temperatures were 4 to 8 o C
cooler during glacial maxima than during
interglacial periods
• -> cooling appears to have more
pronounced effect at lower latitudes
23. Effects on Nonglaciated Areas:
• > in mountainous
regions, snow lines
shifted by as much
as 1000 m in
elevation between
glacial and
interglacial periods
24. Effects on Nonglaciated Areas:
• Resulted in geographic shifts in climatic
zones -> glacial winters were less severe
and glacial summers were cooler and less
subject to heat waves
33. Sea Level Changes in the Pleistocene
• Pygmy Mammoth
• Mammuthus exilis
• Pleistocene Epoch (20,000 years ago)
• Channel Islands of California
• Remains of Dwarfed proboscideans have been
discovered on islands in the Mediterranean Sea, in the
Arctic Ocean off the coast of Russia, and the Pacific
Ocean off the coast of California. The California
species is a descendent of the 12-foot-tall Columbian
Mammoth. When fully grown, the dwarf mammoth
stood only 3.5 to 6 feet tall. Scientists speculate that
the full-sized ancestors of this tiny mammoth reached
the islands during the period of low sea level of the last
glacial period. With sea level lowered as much as 300
feet, the northern Channel Islands (Santa Rosa, Santa
Cruz, and San Miguel) were all part of a single larger
off shore island.
• The Unique ecological aspects of islands, such as
small land area, limited resources, and absence of
large predators, result in interesting evolutionary
products most commonly occurs with large-bodied
herbivores such as elephants and hippos, while
gigantism most commonly occurs with small-bodied
herbivores such as rodents.
• The cast of a nearly complete pygmy mammoth
skeleton shows the actual arrangement of the bones as
they were found on the ground. The original specimen
was discovered on Santa Rosa Island.
38. Refugia and Tropical Diversity
• 1) Not old enough
– Species older than refugia
• 2) Little overlap of areas of endemism
• 3) Cooling uniform across Amazonia
– NOT as fragmented as hypothesized
• 4) Tropics more heterogeneous than
previously thought
39. Refugia and Tropical Diversity
• Climate driven fragmentation may still
have been important Instead of savannah
areas fragmenting tropical forest
• Sea level increases (as much as 100
meters) may have resulted in fragmented
mountaintop islands
43. Proposed Zoogeographic History
of the Bog Turtle
• Fig. 2: Proposed
ancestral distribution and
dispersal routes of bog
turtles.
Clemmys muhlenbergii
47. Biogeographic Responses
to Glaciation
• Pluvial Lakes in Arid Regions
– Resulted from low evaporation rates and high
precipitation
– Basin-and–range topography of Nevada
53. Glacial Cycles and Extinctions
Alternative Explanations for Pleistocene Extinctions
54. Glacial Cycles and Extinctions
• Pleistocene extinctions were not
synchronous
• Climate changes were synchronous
globally
• Does this support the Overkill Hypothesis?
58. Ancient DNA from giant extinct lemurs confirms single origin of
Malagasy primates
K. Praveen Karanth , Thomas Delefosse , Berthe
Rakotosamimanana ¶, Thomas J. Parsons ||, and Anne D. Yoder ,
