Glaciers 2 Flashcards
glacial periods
Earths previous glaciation periods?
the earth has experienced several “ice ages” (glaciation periods) where glaciers have progressed twards the equator to partially (or completely) cover the earth.
What happened during the Precambrian era?
2 ice ages
-Huronian (2400-2100 Ma)
-Cryogenian (850-635 Ma)
What happened during the Phanerozoic era?
3 (4?) ice ages
-Ordovician- Silurian (460-430 Ma)
-Carboniferous- Permian (350-250 Ma)
-[Jurassic- Cretaceous (170-110 Ma)]
-Quaternary (2.6Ma- today)
What is the “Snowball Earth” theory?
it argues that almost all of the earths surface was covered in ice (all continents and a large part of the ocean (up to several; hundred meters))
*presence of glacial deposits on continents that were at tropical latitudes/ near the equator
What would have triggered the “snowball earth”?
- tropical distribution of the continents
- high volcanic activity
- younger sun (not as powerful)
- increase of the atmospheric oxygen level
Explain tropical distribution of the continents?
-continents have a higher albedo (they reflect more sunlight, so when more land is exposed in tropical regions, it starts to reflect more sunlight, less heat is absorbed, cooling the planet further)
-Increased weathering of the continents given their tropical distribution, during the Cryogenian, most continents were located near the equator (Warm, wet tropical climates speed up chemical weathering, especially of silicate rocks) (Rodinia)
*When silicate rocks break down (like feldspar), they react with CO₂ in the atmosphere, this process removes CO₂ and stores it in oceans as carbonates, reducing greenhouse gases and cooling Earth’s climate even more.
Tropical continents → More weathering → Less CO₂ → More cooling → More ice → Higher albedo → Even more cooling
Explain how high volcanic activity would have helped triggered the “snowball earth”
Rodinia breaks up → intense basaltic volcanism.
Basaltic rock weathers efficiently → massive CO₂ drawdown.
(Alteration of basalt through hydrolysis)
Less CO₂ → global cooling → Snowball Earth begins.
*basalt uses 8x more co2 than granite
Explain how a younger sun would have helped triggered the “snowball earth”
-younger sun= fainter sun (younger Sun emits less energy than it does now)
-the Earth was receiving about 6% less solar radiation than today. (significantly lowers global temperatures)
Explain how the increase of atmospheric oxygen level would have helped triggered the “snowball earth”
-Algae photosynthesized (CO2 +sunlight = O2) creating lots of oxygen
-in earths early earth, methane (CH4) was a major GHG, but with more O2, it oxidized into CO2
*this is important because CO2 is 25x less potent, meaning there was a significant reduction in the greenhouse gas effect
(also with ice covered oceans, there would have eventually been less photosynthesis meaning more CO2)
What was it like during the Cryogenian Glaciation
-temp at equator would have been the same as modern day Antarctica
*this temp is maintained by glaciers high albedo (positive feedback)
-few clouds to retain heat since most of the atmospheric water vapor would have been frozen
How did the Cryogenian Glaciation period end?
-no way to remove CO2 (normally rain and silicate rocks help pull CO2 out of the atmosphere, but all land was covered in ice)
-volcanoes kept releasing gases (CO2 and CH4) for 4-30million years (nothing could take the gases out of the atmosphere, so they built up over time)
-CO2 and CH4 are green house gases (they trap heat), so eventually over time they started warming the planet
-the tropics (near equator) started melting first (they get the most sunlight)
-More land=more heat absorption (ice melted, so bare land started to show, land is darker than ice so it has a lower albedo (absorbs more light))
-ice melted fast (within 1000 years ice was gone)
What happened after/ as the glaciers melted
-as the glaciers melted they released tons of glacial debris and rock, these got washed into water and introduced nutrients like phosphorus into the oceans
-phosphorus is a fertilizer for cyanobacteria (which = more O2)
-this increase in O2 and nutrients helped prepare for an explosion of life, so at the end of the Precambrian era there is a huge explosion of biodiversity (Ediacaran biota, one of the earliest complex life forms)
What is the alternative theory to the Cryogenian Glaciation era?
-high obliquity (tilt of the earths axis) - 60 degree tilt (right now it is 23.5)
-would have meant warm poles and cold equator (poles would have pointed almost directly at the sun)
*if this were the case, ice would develop at the equator and would start reflecting sunlight, cooling the earth even further
Explain Quaternary Glaciation
*quaternary is the most recent geological period (2.6 Ma to today)
-the quaternary era is generally considered a cooler period of time
-comprised of at least 4 major glacial periods (separated by interglacial periods)
-Pleistocene is the first part of the quaternary (2.6 Ma - 11,700) this is when the major glaciations happened
-Holocene (11,700 to today) is the warm period after the last ice age (interglacial)
Explain the Wisconsinan Glaciation
-the last of the four major glacial advances during the quaternary
-it is the best known because its effects are still visible today *shaped landscapes, we have evidence (glacial deposits), it affected early humans and animals
How did humans and animals migrate to North America during the Wisconsinan Glaciation
due to the ice bridges from siberia to alaska
How did it form the landscape of North America
-as the glaciers melted, they released huge amouts of water, carving out valleys and river channels
Great Lakes- melting ice left deep carved out basins that filled with meltwater
Champlain Sea (temporary sea covering Québec and Ontario)-weight of glaciers pushed land down, when ice melted land was still low and sea water flooded inland (after time the land rose back up and the sea retreated (isostatic rebound))
St. Lawrence + Ottawa Rivers- as the land shifted from the champlain sea, rivers formed (they follow paths carved by ice and water flow)
Explain Quick Clays
-thick layers of clay that were deposited in the Champlain sea (more than 50m thick)
-consists of “rock flower” produced by glacial abrasion
-composition :
80-90% quatz/feldspar
10-20% clay minerals (phyllosilicates-sheets)
Explain the stability of quick clays
-the silicate sheets possess a negative charge and thus tend to repulse themselves- forming unstable deposits
-however, because they were deposited in a marine enviro, they attract cations to neutralize charges - creating a stable deposit
-the retreat of the Champlain sea and isotonic rebound meant the deposits were exposed to surface waters (rain, snow, meltwaters, etc)-this causes the dissociation of cations and increases repulsive forces- creating unstable deposits (sensitive clay) and therefore creating landslides (soil liquification)
