Karteikarten
The Holocene
Karten in diesem Stapel (25)
- 1When did the holocene begin?11,00 years ago
- 2When was the previous epoch and what was it called?The pleistocene which was from 2.6million to 11,700 years ago
Both the Holocene and the Pleistocene make up the Quaternary period - 3Why is the holocene a special period?1. It's the most recent period - researching and understanding it means we can understand why it has shaped our world today
2. Holocene deposits are much more widespread as there hasn't been the time to erode them and are more intact and easier to interpret
3. It is the period in which early humans started the processes of agriculture - 4Why do we pinpoint the start of the holocene where we do?- The holocene is said to start at the end of the Younger Dryas
- The start of the thermohaline circulation of warmer waters in the Atlantic was captured in ice cores in Greenland at this point
- Although the northern hemisphere saw the period getting warmer the opposite was felt in the Southern (bipolar see-saw)
- The holocene is characteristically not only warmer, but wetter than the last glacial - 5What happened for the 8200 BP event?- The Laurentide ice sheet had reduced in size considerably, but still acted as a barrier to the continent
- Lake Agassiz then burst through
- The sudden draining of the lake into the North Atlantic and subsequent reorganisation of river systems may have caused thermohaline circulation to slow, making the next two centuries much cooler - 6How has orbital forcing changed climate in the holocene period?- The milankovitch cycles are slow, but cause great difference in climate
- Differences in summer insolation is thought to be the biggest driver of the balance of ice accumulation and ablation
- For the northern hemisphere the holocene has been warm summers, cold winters - 7How does solar forcing affect the climate during the holocene?- Recent techniques for measuring sunspots include utilising the correlation between solar activity and the strength of cosmic ray flux
- When sun generated streams of photons collide with atoms in the earths atmosphere, they can cause small nuclear reactions, and this can produce certain isotopes - 14C/10Be
- 11 year "Schwabe" sunspot cycle / 78 year "Gleissberg" and 200 year "Suess" cycle - 8What factors affect the uncertainty of the importance of solar forcing?* The actual magnitude of changes in solar output is very small
* The changes are very small, so only translate to small climate change effects
* It is hard to carbon date for particular times, so it is hard to look at the impacts on a very historical scale - 9Describe the ENSO internal climatic oscillation- The El Nino Southern Oscillation
- A periodicity of around 7 years - caused by a time delay in one part of the Pacific to temperature and circulation in another part
- The delay causes a semi-periodic cycle in sea surface temperatures which then changes air temperature and moisture loads
- There questions to whether there are many other different internal climatic oscillations that could be more appropriate than thinking about sunspot activity - 10Describe the little ice age* Period of noticeably cooler climate between 1350 and 1900
* Europe 0.5 -1 degrees cooler
*Evidence from glaciers showing they were once bigger (relict terminal and lateral moraines)
* Upland European farms abandoned and agricultural decline
* Rivers and lakes froze - ice skating/ curling etc. (Polar bears in Iceland)
*Theories that if it had continued any longer, ice sheets in Canada could have grown to an extent positive feedback would have created a glacial period and its only because of CO2 release this didn't happen (Ruddiman) - 11How has climatic change in the holocene had an effect on Tropical Africa?- Generally differences in glacials and interglacials are least felt at the equator
- Temperatures have seen to have stayed warm enough for rainforest taxa to survive
- Pollen evidence has shown rainforest area has declined - 12How has climatic change in the holocene had an effect on the Sahara?- Lakes filled and there was lush savanna in the south sahara
- The early holocene was much wetter than today because of the enhanced monsoon system
- The enhanced tropical wetness also extended into West Africa and is known as "The African Humid Period"
- As the monsoon began to weaken, it caused the savanna and rainforest belts to weaken and cause the Sahara to be more barren
- The position of the ITCZ seems to be quite variable and delicately balanced when looking at past lake levels, as there seem to be great fluctuations and droughts lasting 10s of years - 13How has the holocene changed European Ecosystems?* During the last glacial, tundra and grassy steppe seemed to dominate
* At the start of the holocene more warm demanding species slowly spread north (trees with lighter seeds did this faster (birch))
* Some species have reader their high-water mark and are now retreating (Hazel in scandinavia)
* Soils become deeper and more fertile
*Early holocene environments richer than they are today with many different animals (lynx, bear, wolves) some of these disappeared because of hunting
* Several attempts recently have revolved around trying to reintroduce different species - beavers especially in order to try to reclaim wetland habitats - 14How did sea level rise in the early holocene change island ecosystems?*Rising sea levels could drown islands or create new ones
-Many sea birds can reside on islands as there are less prey
- Ecosystems can be vulnerable due to resource limits
- Population pressures increased as sea levels encroached land
- Animals bodies become smaller as they don't need large ones for defence and there's less selective pressure for famine
- "Island dwarfing" - Siberia - Mammoths becoming smaller - 15How have hominin moved around the globe - especially before the holocene?- By the end of the last glacial Homo Sapiens were the only species of hominin in the world
- Evidence suggesting there were at least three other different types, but various factors have seemed to have wiped them out (habitat loss, competition for resources)
- Humans entered Eurasia from Africa around 120,000 years BP
- Australasia around 50,000 BP
- The Americas during the late glacial (through Laurentide ice sheet)
- Remote islands then started to be inhabited through the holocene
- Most species nomadic, so very limited impact on the environment (but probably did make some species extinct by hunting) - 16How did the beginnings of agriculture come about?- 2 key components to agriculture
1. Cultivating plants
2. Rearing animals
- Many of these species will have undergone domestication (humans taking control of their reproduction)
- First domesticated animal was the dog - 135,000 years ago (wolves easyish and helpful once trained)
- Unconscious and conscious selections occurred and changed dogs into different breeds
- Domestication marks a qualitative change in the relationship between people and the environment
- Domestication of many other animals in the holocene meant humans could convert biomass they couldn't eat and develop new technologies (cattle)
- In the Near East (during the holocene) they started to select and plant seeds causing development of different cereals etc. - 17What are the social and environmental consequences of agriculture?* The invention of agriculture has seemed to have triggered further human innovations
* Farming community populations boomed rather than being nomadic and relying nature
*Goods are accumulated in farming communities - more innovation and hierarchal structure to society
*People developing other skills than having to concentrate on finding food - pottery/ woodwork and in 2nd half of holocene, metal
*Some societies became more wealthy = stratified communities (high leaders)
*Large scale projects able to be co ordinated - irrigation systems, buildings - 18Why is the industrial revolution (1800) seen as a turning point?- Impacts of post industrial activity on the environment are massive
- Before the time there is the image that people lived in harmony with nature
- Arguments this wasn't the case as many old civilisations deforested large areas of land/ reduced biodiversity/ altered drainage/ introduced new species/ eroded
-Many previous collapsed societies because of the environmental strain - Easter Island because of deforestation - 19How have humans caused deforestation?- Human lineage comes from fruit eating apes, we still find it difficult to digest cellulose and raw meat. Fruits aren't year found (apart from in tropics)
- Farming has produced a method which means we can turn energy from the sun into a form we can eat
- Inedible forests are replaced with fields or grain or pasture
- Forest therefore turned into a cultural landscape
- Pollen diagrams show the coming of farmers = tree pollen decline - 20What are the ways deforestation is initiated?1. By axe
2. In dry environments it can be burned
3. Allow animals (sheep and goats) to eat saplings and the pigs can clear roots - over the decades, woods around pastoral areas tend to thin
4. Over a very long time, even collecting bits of timber for firewood can have an effect - 21How has deforestation by humans effected the ecosystem?- Forests are 3-D structures - harbouring plants and animals that otherwise wouldn't be able to survive without there shade and nature (not in pastural land which is 2-D)
- With deforestation, total biomass declines, carbon is released as burning occurs
- Atmospheric CO2 up in the holocene as a result
- Without clearing lots of land, there would have been little land for food for humans
- Forest has been romanticised - stories of bandits etc
- Woodland seems favoured - they provide good sources of timber, seasonal nuts and fruits and animals for hunting
- Woodlands are now carefully managed - regular coppicing and pollarding with legislations in place - 22How have humans contributed to soil erosion and impoverishment in the holocene period?* Overuse of land has caused erosion of soils and consequent impoverishment of the soil resource
* After deforestation, if the land is exposed to rain splash from the lack of canopy, erosion happens at faster rates
* Soluble nutrients like P aren't lost to leaching
* Erosion is particularly prominent on sloping terrain - in the Med basin, overgrazing has lead to an almost total loss of the very thin soils
* Soil can simply be blown away as well (40% of Iceland's soil stripped since 870AD)
* Eroded soils aren't all lost - they are often redeposited into rivers and onto floodplains - one places loss is anothers gain
* Clay based soils can remain intact if the area is slightly wet so that it becomes sticky
*Soluble materials can get washed away quickly and make the soils then more acidic, encouraging colonisation by bog plants. Some absorb water, making the soils wetter (more likely to be anaerobic) so plant litter decays more slowly - leading to the beginnings of peat growth - 23How have humans changed irrigation and drainage in the holocene period? (Wet areas)- Waterlogged basins can be as much of a problem as aridity for plants
- Fenlands of East Anglia famously irrigated by the Romans
- In 17th and 18th centuries, first wind power and steam systems were developed to pump water out of the low lying fens
- Rivers straightened so would drain into the sea easier
- Earth banks to constrain floodplains
- Each field has own drains and ditches
- The drained soils off the fens made good farmland
- Peat can now be more that 90% water weight - loss of water causes it to shrink
- Dry peats become vulnerable to wind erosion
- As peat drys, oxygen rises, causing increased aerobic decay, so peat gradually oxidised to CO2 gases
- Thousands of ponds, fens and marshes (boggy land) have been reclaimed by agriculture and now there is a strong drive to conserve them - 24How have humans changed irrigation and drainage in the holocene period? (dry areas)* Many past "hydraulic" civilisations (Mesopotamia) developed on the basis of their command on water supply
* River courses have been diverted for over 10,000 years
* Embanking and arranging fields so that they allowed the retention of water and flow of water to one field to another were early developments
* Combinations of hot climates, fertile floodplain soils and controlled water supplies made farming techniques very productive
* Disputes over water rights, politically difficulty of building/maintaining shared resources has led to conflict
* In arid areas, excessive evaporation of irrigated fields can draw salts upwards, eventually making them toxic to plants - 25—
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- Karteikarten am The Holocene , erstellt von ph133132 am 11/11/2015.
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