Lecture 13: Descent in to the Icehouse Flashcards
What happened to the continental land masses in the Cretaceous-Cenozoic transition?
They slid across the planet to positions more recognised today
What happened to India in the Cretaceous-Cenozoic transition?
Over a period of 90-20mya it travelled to the continent of Asia from deep south.
What happened as a result of India colliding with Asia?
formation of Himalayas and Tibetan Plateau
What is the Himalayan uplift hypothesis?
The uplift of these mountains caused the physical and silicate weathering to increase
What effect would the increased weathering rate have on global climate?
reduced GHG, increased cooling. Much later reversed by negative feedback between cooling and temperature (colder means less weathering
What happens to carbon that is weathered out of the earth rocks? What does it lead to in oceans?
It combines with the precipitation to form an acid where it flows in rivers increasing weathering rates which releases ions such as calcium and magnesium. When both ions and carbon enter the ocean biology combine them to form carbonates
What evidence was found by France-Lanord and Derry (1997) that confirmed that silicate weathering was taking place as a result of the Himalayan formation?
Discovery of ions in the river and (inorganic) carbon in the channel that would then flow out in to the oceans to form carbonates
What did France-Lanord and Derry (1997) propose was however a bigger burial of carbon?
More (organic) carbon was buried and prevented from interacting with interacting with the atmosphere through sediment burial.
Where and how was the organic carbon in the Ganges and Brahmaputra buried?
the clay and gravel eroded from the channel would either contain organic carbon in it or when it would reach the deltas it would bury the organic carbon that was stationed down on the delta. Either way the organic carbon would be buried and prevented from interacting with the atmosphere
Furthermore, what undermined the theory proposed by France-Lanord and Derry (1997) about how the formation of the Himalayas would increase weathering?
The erosion rate, in light of long-term geological calibration and contextualisation, does not appear to have increased.
What explanation was provided for why the Himalayas had not increased weathering rates?
It had been counterbalanced by an increasingly cooler and drier climate that are not ideal conditions for weathering
What was another piece of evidence that undermined the suggestion that the Himalayan formation had increased silicate weathering and led to the reduction of atmospheric carbon?
Carbon dioxide concentration records appeared to have been relatively stable over a long time period
What date is atmospheric CO2 estimated to have reached the present level?
25mya
What evidence is there that suggests there must be another factor other than CO2 influencing the climate?
There have been times when the temperature and CO2 records appeared to diverge.
- CO2 stabilised from 25mya, while climate fluctuated
- Early record (Oligocene) there was a massive CO2 peak, while temperature decreased
What might explain why there does not appear to be a matching up of CO2 and climate record, other than they are not related?
It is dependant upon pockets of previous evidence which are difficult to find and analyse.
What are the two ways CO2 is proxied?
Foraminifera: shell formation consists of carbon
Fossil Stomata: When CO2 is low, plants have more stomata, when high CO2 less stomata
What are fossil stomata and why do they open and close dependant upon CO2 levels?
Holes in the plant leaves that can be opened by plant to receive CO2. If there is less CO2 then they need more holes to extract the little CO2 that exists
How do we know that stomata act in the way they do to CO2?
Comparing Stomata from 18th Century when it was known colder to today
What recent development has allowed more agreement between scientists about previous changes in climate and CO2?
improvements made to accuracy of different proxies
What is one period of disagreement that still exists and why?
15mya - because stomata suggest a spike in carbon concentration, while other proxies show stable levels (e.g. Phytoplankton)
What do proxies of CO2 suggest was happening during the Miocene?
concentration was decreasing, but starting to stabilize
What do studies in to the relationship between primary productivity of plants and CO2 changes suggest?
If CO2 decreases, there is a bigger impact on primary productivity than if CO2 decreases
Why do CO2 decreases affect plant primary productivity more than increases? What feedback does this form and who studied it?
Pagani et al. (2009). when CO2 concentration reaches critical low level, plants will shut off reducing their ability to carry out normal functions. weathering they enact will decrease,meaning more CO2 in atmosphere. This therefore forms a negative regulating feedback.
When were the first desert grasslands dated to?
33Mya
When were the first Ungulate grasslands dated to?
17mya
When were the first C4 grasses dated to?
7mya
Why were grasses able to emerge?
Climates were colder and drier (due to fall in CO2) which they are more tolerable to compared to other plants. There was also co-evolution of them with animals such as horses that facilitated each others evolution
What makes C4 grasses particularly strong?
They can survive when the concentration is especially low
Describe the vegetation transition in to the Pliocene?
from Savannah grasslands to more abundant trees and animals
Why was the transition in the Pliocene so important?
because it played an important role in our development - natural selection favoured animals that could stand up and walk across the new tree landscape
Where have the earliest remnants of hominina discovered?
Great African Rift Valley
When was our divergence from the chimpanzees dated to?
6mya
What are 5 different categories of hominina that developed following the divergence from the chimpanzee?
Ardipithecus, Australopithecus, Praeanthorpus, Paranthorpus and Homo
What and where are the first cases of people standing up right dated to?
3.7mya Tanzania
If people were standing up what does this suggest about their evolution?
Skeletal changes
When and what were the first stone tool making hominins dated to?
2.5mya homo habilis
What was the skull size and brain capacity of the first stone tool making hominins? (Homo habilis)
1/3
What were homo erectus and when were they dated to? why were they more intelligent?
upright man dated to 2mya. they discovered fire, hunted in groups for larger prey such as mammoths and trading tools
When were the first homosapiens thought to have emerged?
100kya
what is the closest relative to the homosapiens and coexisted with them?
homo erectus
