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Intro to Earth Science > C-Snowball Earth Events > Flashcards

C-Snowball Earth Events Flashcards

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1
Q

What are the 4 key geobiologic events in the Earth’s history?

A

Rise of Oxygen
Snowball Earth
Rise of Animals
Conquest of Land

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2
Q

What did palaeomagnetic data reveal to Dawn Sumner from a sample about a late Neoproterozoic glacial deposit sample from the Elatina Formation in Australia?

A

It was formed at low latitudes (near equator) and low altitudes (possibly high ones too)

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3
Q

What did the evidence of glacial deposits at the equator mean for the rest of the planet?

A

Snowball Earth

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4
Q

Did Snowball Earth only happen once?

A

No, it happened 3 times.

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5
Q

Name the 3 different glaciations (from youngest to oldest)

A

Marinoan glaciation
Sturtian glaciation
Huronian glaciation

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6
Q

When did the Marinoan glaciation occur (approx)?

A

650-635 mya

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7
Q

When did the Sturtian glaciation occur (approx)?

A

730-720 mya

May have lasted 60 mil years

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8
Q

When did the Huronian glaciation occur (approx)?

A

2400-2100 mya

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9
Q

Why did the glaciations happen when they did? (3)

A

Possibly plate tectonics - break up of supercontinent Rodinia creating cluster of continents (750mya) at low palaeolatitudes (higher albedo as land reflects more solar radiation than water)
More solar radiation at equator than poles so high albedo
Induces global cooling

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10
Q

What is the possible role of weathering in glaciations? (4)

A

Chemical weathering most effective in equatorial climate (high precipitation and temps)
Bicarbonates transferred to oceans (locked away in rocks)
If lock down greater than release of CO2, then CO2 removed from atmosphere
Triggers global cooling

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11
Q

What is the ice-albedo feedback?

A

Positive feedback loop between amount of ice on Earth and its average temps
Eg. if a lot of ice on earth, reflects more solar radiation, Earth continues to cool
If less ice on earth, reflects less solar radiation and absorbs more, Earth continues to warm up

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12
Q

Where is the Storeelv and cap dolostone (cap carbonate) example?

A

Kap Webber, Andree Land, Fjord Region, East Greenland

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13
Q

Where is the Younger Cryogenian cap-carbonate example?

A

Windermere Supergroup, Shale Lake Section, Mackenzie Mtns, NW Canada

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14
Q

Where is the contact between marine Ghaub Fm and Keilberg Mb example?

A

Otavi foreslope, N Namibia

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15
Q

What is the geological record of the Snowball Earth Event?

A

Varies in detail

Same general stratigraphy (stratigraphy after and before even is when it begins to differ

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16
Q

What is the stratigraphy of the Snowball Earth Event from top to bottom?

A

Cap Carbonate Sequence (after event)
Glacial deposits - diamictite on top then Banded Iron Formations (during event)
Varied sediment reflecting environment (before event)

17
Q

What are diamictites?

A

General name for very poorly sorted lithologies

18
Q

What does IRD stand for?

A

Ice Rafted Debris

19
Q

What supporting evidence is there of glacial phases? Name and give and example (5)

A

Glacial marine tills, Ghaub Fm, Namibia
Ice-rafted debris, Ghaub Fm, Namibia
Scratched pebble, Jbeliat tillite, Mauritania
Glacial tillite and pavement, Smalfjord Fm, N Norway
Ice-rafted dropstone in Banded Iron Formations, Sayunei Fm, Rapitan Gp, Nt, Canada

20
Q

Why is there a return to Banded Iron Formations?

A

Occurs during episode of ice-covered sea - Fe2+ builds up in ocean
When ice retreats (for short time) O2 introduced to water and BIFs form

21
Q

What are benthic fans?

A

Crystal precipitates growing upwards from seafloor

Eg. Namibia, Canada

22
Q

What are features of cap carbonates? (3)

A

Giant wave ripples (W Australia)
Stromatolite build ups
Benthic fans (Namibia, Canada)

23
Q

How do you escape a Snowball Earth Event?

A

Need to get CO2 back into atmosphere

Carbonate-silicate geochemical cycle

24
Q

What occurs in the carbonate-silicate geochemical cycle that saves the Earth? (5)

A

Weathering stops in Snowball Earth due to ice cover
So CO2 emitted from volcanoes builds up in atmosphere
Eventually enough CO2 means sea ice begins melting at low latitudes
Open ocean water absorbs solar radiation
Creates positive feedback loop and greenhouse conditions continue to establish

25
Q

What occurs to form cap carbonates? (3)

A

Huge volumes of ice-produced material available for erosion and weathering
Precipitation of carbonate materials as cap carbonate (after event!!)
Over time equilibrium re-established

26
Q

What is the aftermath of Snowball Earth?

A

Hothouse Earth

Intro to Earth Science (13 decks)

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