Cenozoic Ice Age (final exam) Flashcards
When was the warmest time in the Cenozoic? Explain this time- What were the causes of this?
It was the end paleocene thermal maximum (highest temp reached at the beginning and temperature continuously dropped)
The deep sea briefly became very warm
Causes:
- greenhouse warming
- ocean circulation changes
- dense forests at high latitude
When did the Paleocene thermal maximum begin to cool? Explain this cooling > what were the causes?
- cooling began in later Eocene to beginning of Ice Age at about 40 million years ago (start of antarctica ice)
> cooling of surface waters in high southern latitudes (cooled deep water by about 10 degrees celsius
Causes:
- closure of Tethys sea
- break-up of Antarctica and Australia complete 30 Ma
*reasons for the cooling are geography related
Explain the modern glaciation events
- brief pliocene warming followed by gradual cooling
- formation of continental ice sheets in northern hemisphere around 2.6 million years ago *modern ice age
- at least 20 warm-cold cycles
- today the glaciers cover about 10% of the earth’s surface
What period is the recent/holocene epoch in?
the quaternary period
What is the pleistocene paleogeography like?
it is essentially how it is today
What are glaciers and how do they move?
They are moving rivers of ice > they move by plastic flow (internal deformation of ice in response to pressure) and basal slip (sliding over its underlying surface)
Valley glaciers (mountains)
Continental glaciers (ice sheets)
What are two of the Pleistocene glaciers?
Susitna Glacier in Alaska - smaller glaciers joined to form
The penny ice cap on Baffin island, Canada, covers about 6000 km2
Describe the glaciers during the Pleistocene
The Pleistocene experienced major glaciations separated by warmer interglacial periods
At their most extensive, Pleistocene glaciers covered 30% of the Earth’s surface
The sea level was 130m lower
How do glaciers form? what kind of rocks are glaicers?
They form in areas that receive more snow in the winter than melts in the summer
Snow buried within a glacier converts to glacial ice
When the ice reaches 40m thick, it begins to flow in response to pressure and becomes a glacier
If a glacier’s budget is balanced (amt of snow accumulated = snow waster), its terminus remains in the same position
However, if the budget is positive, the terminus advances, and if the budget is negative, the terminus retreats
*glaciers are metamorphic rock > can think about them in terms of the rock cycle
What are the evidences for glaciation?
- pollen (found in grains in ice)
- till (moraines) - landforms composed of unsorted glacial sediment (till) deposited by or from a glacier
- erratic boulders
- outwash deposits
- scouring (U-shaped valleys)
- glacial lakes (lakes now that were formed by glacial activity)
- Isostasy (the earth’s crust’s response to changes in ice load, causing the land to sink under the weight of glaciers and rebound as they melt)
- sea level changes
- marine sediments and fossils
What are the other 2 types of lakes (other than glacial lakes)
Pluvial lakes:
- large lakes far from glaciers
- formed by increased precipitation
Proglacial lakes:
- large lakes next to glaciers
- formed by meltwater ponding
Explain the formation of the Great Lakes (before and after the Pleistocene)
- before the Pleistocene, the great lakes region was a flat lowland with broad stream valleys
- pleistocene glaciers covered and deeply eroded the area
- four of five great lake basins were eroded below sea level
- as the glacial ice retreated northward, the lake basins began filling with meltwater
- the great lakes are considered glacial lakes > they were caused by glacial activity
How long did Glacial Lake Agassiz exist and describe what the area is like now
Existed for 2700 years
Drained abruptly 8200 years ago > led to an estimated 2m global sea level rise
Now: Exposed mud-rich, extremely flat land and proglacial lakes in Manitoba
What is the Bering Land Bridges connection to glaciers?
- ancestors of indigenous North Americans reached North America by walking across the land bridge
- some may have arrived by boat, following ancient coastlines
- glaciation caused the drop in lea level > causing the exposure of this land bridge
Glaciations are ___ common in earth’s history
not
What are some theories for what would’ve caused the Pleistocene glaciation? (long-term climatic changes or things that cause cooling)
*There is not 100% explanation for the Pleistocene glaciations
Long-term climatic changes on continents: plate movements, orogenies, and changes in sea level
Things causing cooling: Decreases in atmospheric C02, other greenhouse gases
Milankovitch cycles?
What are Milankovitch Cycles (what can they predict)
Milankovitch proposed that predictable deviations in Earth’s orbit and rotation/axial tilt (Milankovitch cycles) can sufficiently alter the amount of solar radiation hitting the Earth and affect climates > can partially explain intermediate climate changes lasting few thousand to a few hundred thousand years
What are the 3 key elements of the Milankovitch cycles?
Eccentricity:
- shape of Earth’s orbit is elliptical, not circular
- summer in one hemisphere, winter in the other, changes throughout the year
Earth’s axial tilt:
- axis of rotation is not perpendicular to equator
- changes amount of radiation that reaches the poles
Precession of equinoxes:
- time of year Sun is directly over equator changes over time
- can increase/decrease maximum solar radiation at high latitudes by 15%
