Lecture 3 – Evidence for past Climates 2

Question 1

When was the earliest evidence for liquid water found?

Answer 1

3800 Ma ago

Question 2

What does surface water being present throughout history imply?

Answer 2

That the global average temperature is greater than 0 degrees
The existence of at least a modest atmosphere (otherwise the water would evaporate)

Question 3

What is the evidence for Earth being sufficiently cool for liquid water 4.4 Ga ago?

Answer 3

We have found zircon (dated using radiometric absolute dating)
Its chemical composition indicates that the Earth was cool enough for liquid water (rather than being a sea of molten magma)

Question 4

What is the evidence for water lain sediment and the oldest fossils we have found?

Answer 4

Both were proven the same way
We have found interlayers of iron oxide and chert laid down in oceans
This is likely because of oxygen producing bacteria
We dating them using radiometric dating of the zircon in adjacent rocks (principle of superposition)

Question 5

What is the aim of a climate reconstruction tool?

Answer 5

either to date or give environmental information, or both

Question 6

What is special about how certain sediments develop?

Answer 6

develops from very specific background environments, e.g. tropical coral reefs develop from tropical seas

Question 7

What does the idea of interpretation of past environments based on current evidence hinge off?

Answer 7

The idea that modern day sedimentary and biological processes reflect climatic environments

Question 8

How do limestone and coral reefs reflect past climate?

Answer 8

Limestone and coral reefs would have formed in a tropical sea

Question 9

What does the variation in rock characteristics compared to their environment now suggest?

Answer 9

environmental/climate change (in terms of space and time) rather than climate consistency

Question 10

What is using sedimentary structures useful for identifying?

Answer 10

particularly useful for materials like sands which can originate from multiple sources

Question 11

What sedimentary structures can we interpret in sands?

Answer 11

‘cross-laminations’ in the landscape to give us information, e.g. deserts have very large cross laminations

Question 12

What features can we look at in sands for information?

Answer 12

Current environment, sedimentary structures, composition and textural maturity

Question 13

What does rounded sand grains suggest?

Answer 13

Rounded sand grains suggest a desert environment, because the wind is more abrasive

Question 14

What do less rounded sand grains suggest?

Answer 14

less rounded grains suggest a fluvial environment with less extreme winds

Question 15

How can we sue what material is left over to give us information?

Answer 15

We can see what type of material is left over, e.g. only the most resistant material. This suggest there is strong abrasive winds, which would suggest a desert environment, or if they are present, it is likely a fluvial or marine environment

Question 16

How can we tell desert from fluvial from marine environments?

Answer 16

Associated features, e.g. a fossil fish suggests a Calcrete forms in semi-arid environment, ruling out an ocean environment

Question 17

What environment do glacial cirques form in?

Answer 17

Cold

Question 18

What are glacial cirques (+ example)

Answer 18

These are bowl-shaped mountain side landforms which open downslope and are bounded upslope by a cliff E.g. Kinnerly peak

Question 19

When does a glacial cirque form?

Answer 19

when hollows are sheltered from heat – leading to an accumulation of snow and ice, and ultimately glaciers

Question 20

What does the lowest cirque floor of a contempoary cirque tell us?

Answer 20

The snowline

Question 21

How can we compare ancient and current snowlines?

Answer 21

Ancient snowlines can be compared with present day snowlines and them temperature changes calculated

Question 22

Where do sand dunes form?

Answer 22

Warm environments

Question 23

What are sand dunes

Answer 23

Accumulations of wind-blown particulates

Question 24

What does sand dunes tell us about precipitation

Answer 24

Less than 100mm per annumm

Question 25

What happens if there is more than 100mm of rainfall per annum in a desert?

Answer 25

vegetation cover reduces sand movement and encourages soil development

Question 26

Where are fossil sand dunes found?

Answer 26

currently found in areas of high rainfall (suggesting rainfall has increased since)

Question 27

What are Tuyas?

Answer 27

Volcanoes consisting of a steep pile of fragmented material, with near vertical cliffs of lava near the top and a flat summit

Question 28

When do tuyas form?

Answer 28

When an eruption occurs under a glacier, melts through it and emerges out the top

Question 29

What is permafrost?

Answer 29

Permanently frozen ground for 2 years or more

Question 30

How thick can permafrost ice be?

Answer 30

Can be more than 1km thick

Question 31

What % of the Earth’s surface is covered by permafrost?

Answer 31

25%

Question 32

What must be true for a land to be in permafrost?

Answer 32

Ground (soil, sediment or rock) must be at, or below freezing point of water for 2+ years where only the superficial layer (activate layer may thaw out during the summer)