Glg 412: Ice Ages

Front 1

Ice Ages

Back 1

• The ice ages occur during the Pleistocene Epoch (~2MA – 10,000 years ago)
• Several separate intervals of large scale guild up of ice ( not as extensive as snowball/Slushball Earth)
• Main effects in Northern Hemisphere, also South America, Australia
• Maximum spread of glacial ice was about 18,000 years ago

Front 2

Ice Ages: What Happened?

Back 2

o Decrease in solar radiation
o Changes in weather/ocean current patterns
o Slight shifts in Earth’s orbit around the Sun
o Increased volcanic activity producing dust in the atmosphere
o Probably a complex combination of these factors

Front 3

Ice Ages

Back 3

Ice ages saw many temperature fluctuations
o Periods of cold temperatures and ice advance, separated by warmer Interglacial periods

Front 4

Ice Ages

Back 4

Latest glacial advance was Wisconsinan
o Ice free corridor in Canada
o It is during this period that humans first reached

Front 5

Ice Ages

Back 5

North America
Sea level drop during the Wisconsinan glaciation was sufficient to allow Beringian land bridge to be above sea level between Siberia and Alaska
o Acted as a dispersal corridor for biotic exchange between Asia/North America

Front 6

Ice Ages: Glaciers during this time had many impacts on the landscape

Back 6

o Mountain valleys
o Large moraine deposits (long island)
o Glacial lakes
o Great Lakes

Front 7

Ice Ages:

Back 7

Sea level change has affected Florida over the last 5 million years

Front 8

Ice Age: Mega Fauna

Back 8

• Ice Age Mega Fauna
Wooly rhino, Mammoth, Glyptodont, Irish Elk, Cave Bear, Saber Tooth Cat or Panthera atrox

Front 9

Panthera atrox

Back 9

-Largest lion known
-About 25% larger than African lion
-Up to 13 feet long, 5 feet tall at the shoulder
-Lived in western N America up to ~10,000 years ago
-May have sheltered in caves during cold winters
-Many specimens recovered from the La Brea Tar Pits in Los Angeles

Front 10

Ice Ages: La Brea Tar Pits (downtown Los Angeles)

Back 10

o Naturally occurring deposit of tar seeping to surface
o Trapped many animals looking for water, and then also trapped predators trying to get to potential prey
Sample skewed towards predators
o Tar has preserved the skeletons, which occur in great abundance

Front 11

Ice Ages: Mastodons & Mammoths

Back 11

Mastodons
o Forest browsers
Mammoths
o Grassland grazers
o Frozen baby Mammoth from 37,000 years ago
-Well enough preserved to extract DNA
-Can do internal scan of body anatomy using CT-scans

Front 12

Ice Ages: Michigan

Back 12

Michigan was covered by glacial ice during maximum ice extent
o Glaciers responsible for more flat landscape and many kettle lakes (Includes lake Lansing)
o Mammoth, Mastodon, and other large animals are found in lower Michigan

Front 13

Ice Ages: Australia’s Pleistocene Megafauna

Back 13

Giant Wombats, Flightless birds, Huge Lizards, Marsupial lion, Marsupial ground sloths

Front 14

Ice Age: Australia's Megalania

Back 14

Giant fossil varanid (monitor lizard), dominant apex predator
o Reached length of up to 8 meters
o Lived in Australia during the Pleistocene, until 40,00 years
•Australian biologist Tim Flannery suggested that in order to recreate the Pleistocene of Australia, Komodo Dragons could be introduced into Australia as the ecological equivalent of Megalania

Front 15

Ice Ages:

Back 15

• The Ice Age “megafauna” mainly dies out at the end of the Ice Ages ~10-12,000 years ago
• Extinctions approximately coinicide with major retreat of the glaciers

Front 16

Ice Age: North America Extinctions

Back 16

In North America ~ 70% of large mammals go extinct at this time
o Mammoths and mastodons
o Giant cave bears
o North American camels
o Giant ground sloths
o Wooly rhinos
o Glyptodonts
o Saber toothed cats
o Horses

Front 17

Ice Age: Reasons for mass extinction

Back 17

o Catastrophic explanation – human over hunting
o Vs natural environmental change

Front 18

Ice age: extinction possible reason 1: Pleistocene overkill

Back 18

-Early humans hunted the ‘megafauna’ so effectively that they drove most of the large mammals to extinction
-Consistent with the spread of humans in North America, and large mammals would have been appealing targets
Some problems with this idea

Front 19

Ice age: extinction possible reason 1: Pleistocene overkill- problems with theory

Back 19

Almost no direct evidence of kill sites
• In Australia, humans arrived long before the extinctions happened
• Some of the species that went extinct would not have been targeted by hunters (small, not appealing)
• Human populations were still very small

Front 20

Ice age: extinction possible reason 2: natural

Back 20

o Climate changes as the ice sheets retreated had a major effect on the large mammals that had adapted to living in periglacial environments close the glaciers
o But plants and small animals not as strongly effected… why?
o Earlier glacial retreast

Front 21

Ice age: extinction & Survival

Back 21

• It is really the case that many large mammals went extinct at the end of the ice age for reasons that related to their large size?
o It has been suggested that those animals with slow reproductive rates, independent of their size, were other ones most likely to go extinct
o Fast breeders an

Front 22

Ice age: Last Surviving Mammoth & Mega Fauna

Back 22

Dwarf species, much smaller than regular mammoths
-About 3,700 years old, Wrangel Island, Arctic Ocean, west of Alaska
-Alaska and Siberia serve as a refuges for the last surviving ice age megafauna
-Musk ox en are ice age megafauna survivors in Alaska

Front 23

Ice Age: Today

Back 23

Technically, we still are in an Ice Age because ice sheets still cover Greenland and Antarctica, as well as major glaciers in high mountainous regions

Front 24

Are Ice Ages and other major climatic events in Earth’s history caused by cyclical changes in orbital dynamics?

Back 24

Milankovitch cycles
-Hypothesized that axial tilt, axial precession [change in Earth’s rotational axis] and eccentricity [wobble] in Earth’s orbits happen on a cyclical basis and these changes have affected Earth’s climate over long periods

Front 25

Ice Age: Milankovitch cycles

Back 25

-Precession varies every 19-24,000 years
-Eccentricity varies 100,000 and 41,3000 years
-Tilt [obliquity] varies 41,000 years
-Correlation of Milankovitch cycles and glacial episodes over the last 1 million years
-The clearest of the Milankovitch cycles with respect to glaciation is the 100,000 year cycle of orbital eccentricity , which has been hypothesized as resulting in 10,000 year ice age cycles over the past million years.

Front 26

Ice Ages: Milankovitch cycles affect polar ice caps on Mars.

Back 26

Mars wobbles far more than Earth
• Snowball Mars
o There is evidence for glacial deposits along the flanks of mountains in the Martian tropics, near equator
o Date to ~5Ma, when Mars was extremely tilted on its axis creating very cold and long winters, tilt was extreme enough that Mars was lying on its side, with poles facing the Sun