Ice and life

Question 1

What is the faint sun paradox?

Answer 1

the sun has gained considerable size and luminosity since earth formation (25-30% more warmth)

Question 2

What is one proposed idea for why earth temp wasn’t below freezing at earth formation?

Answer 2

potentially due to high levels of ghgs but its said that lithosphere might not have been able to support the required levels

Question 3

Beside higher ghg levels what might have been another reason for the absence of an early freeze?

Answer 3

low albedo due to the close proximity of continental land mass leaving lots of ocean (energy absorbing) surface to maintain temp

Question 4

What was the first glaciation event?

Answer 4

Huronian 2.3 billion years ago

Question 5

How has the maximum age of the Huronian been dated?

Answer 5

From lava s at the bottom of the sequence which can be radiometrically dated

Question 6

How has the minimum age of the Huronian been dated?

Answer 6

An intrusion which runs through the rock sequence

Question 7

How many glaciations were there in the Huronian event?

Answer 7

4 (3 in Canada and 1 in Africa)

Question 8

When did the Neoproterozoic glaciations occur?

Answer 8

After the boring billion

Question 9

What periods within the Neo-Proterozoic are focussed on for life and glaciation?

Answer 9

Cryogenian (colder period)
Ediacaran

Question 10

What will modern glacial sediment look like?

Answer 10

Fine grain rock flour (produced by milling of rock) which holds a boulder matrix
Striated (scratches) and faceted (smoothed face)

Question 11

What is an example of the global application of glacials (tillites)?

Answer 11

Australia has 2 distinctive tillites separated by a magnesium carbonate (dolomite)
The younger = Marinoan
Older = Sturtian

Question 12

What can be noticed with the global distribution of the Marinoan and the Sturtian?

Answer 12

They pretty much cover all modern day continents in how they are distributed this is because when the land was in a supercontinent most land was glaciated around the equator at ocean level showing planet was cold

Question 13

What is panglaciation?

Answer 13

glaciation at sea level at the equator

Question 14

How many ice ages were in the Neoproterozoic era?

Answer 14

2 ice ages in the Cryogenian and 1 in the Ediacaran

Question 15

What are the different models for Neoproterozoic (Cryogenian) glaciations?

Answer 15

Snowball earth
High-tilt earth
Slushball earth
Zipper-rift earth

Question 16

What is snowball earth?

Answer 16

Earth is covered in km of ice

Question 17

What is slushball earth?

Answer 17

not as cold as snowball with some unfrozen areas

Question 18

What is high tilt earth?

Answer 18

Earths tilt has changed and that at one point present equatorial location was more polar promoting glaciation

Question 19

What are the first order controls on planetary climate?

Answer 19

Solar insolation
Albedo
Atmospheric green house gas forcing

Question 20

Why did glaciation occur in the Cryogenian?

Answer 20

supercontinent Rodina split apart and became wetter lowering atmospheric co2 (due to moving continents shifting weather patterns)

Question 21

What would have counteracted runaway ice-albedo feedback?

Answer 21

CO2 builds up in the atmosphere from volcanoes causing warming and leading to abrupt end to glaciation

Question 22

What are some rock structures linked to life in the Edicaran?

Answer 22

Wobbles
blobs
Scratches

Question 23

What is one of the largest life evidence from the Edicaran?

Answer 23

Charnia

Question 24

Why cant the charnia be thought of as a paleo-seapen?

Answer 24

As sea pen the older material is at the bottom near the stem this is the opposite for charnia with older material at the tip

Question 25

What are Doushantou embryos?

Answer 25

sourced from dissolved limestone suggested they might be sponges or red algae or even multicellular but unknown

Question 26

What is a kimbrella?

Answer 26

Candidate from an early mollusc

Question 27

What is a springina?

Answer 27

interpreted as an annelid worm (proto-arthropod)

Question 28

What is the summary for Ediacaran life?

Answer 28

hard to interpret macrofossils
Majority life = sessile ‘vendobionts’ on surface
Some potentially metazoan