Introduction 1 Holocene or recent interval a It is very brief geologically speaking i 11 700 years of the Earth System history b Humans i Conquer the world ii Affect the environment 1 Hunting 2 Cutting down trees 3 Planting crops 4 Building towns 5 Burning fossil fuels 6 Creating communication and transportation networks c Precise timing of events possible i Sediments and fossils are fully within the range of radiocarbon dating d Most species of plants and animals still exist today paleontologists can use the Holocene fossil records to reconstruct paleo habits within great accuracy 2 Important to understand a Reveals how the earth system has approached the present state b Future changes due to Holocene trends c Speed of change Holocene 1 Retreat of glaciers from LGM a Modern ice age began on the Oligocene ice in Antarctica b Intensified in the late Pliocene NH glaciers 3 1 Ma c Since i Many cycles of ice sheet advance retreat in the Arctic and Antarctic ii LGM peaked 18 Ka d LGM ice sheets began to retreat 15 Ka e Southern terminus of the Laurentide Ice Sheet on NA 13 5 9 5 Ka i As the ice sheet contracted SL rose ii Meltwater ponded in depressions scoured by ice sheet advance iii The Great Lakes of NA are remnants of these proglacial lakes f Prairie Potholes across southern Canada i Former sites of stagnant ice as the ice sheet retreated ii Proglacial sediment accumulated in front of glacier from meltwater streams Abrupt global events 1 Two major events considered abrupt in the Holocene a Vegetation changes b Eustatic SL rise 2 Vegetation change a Tundra and forests shift global positions as ice retreated i Transition to interglacial climatic conditions b A warming climate changed southern floras 12 Ka 3 Abrupt SLR occurred as the Laurentide Ice Sheet melted a Climate warmed ice melted but not at a steady state b Unsteady ice sheet ablation loss of ice caused SLR in abrupt steps 4 Corals record the pattern of post LGM SL change a Series of drowned corals evidence of three episodes of rapid SLR in the Holocene i Can radiocarbon date correlated with elevation b Comparison of water depth with age of the corals SL has risen 120 m in the last 20 Ka 5 The Younger Dryas a Near full glacial conditions in the NH 12 9 11 6 Ka b Annual ice layer thickness measured from the Greenland Ice Sheet ice core changed between 17 5 and 9 5 Ka i ii In cold regions thicker annual layers of snow when the climate warms If the cold climate cools thinner annual snow layers c Change from thin to thick annual snow layer climate warmed d abruptly 15 Ka Initially gradual cooling thinner annual layers abrupt change to thinner annual layers 12 9 Ka beginning of the Younger Dryas YD e At 11 6 ka thickness of annual layers increased abruptly in three years indicating an abrupt warming and marking the end of the cold YD Start of the Holocene f 6 What caused the onset of the YD 12 9 ka a Two hypotheses b Change in ocean currents i Fresh water input from melting ice into Atlantic 1 Obstructed the flow of warm saline water from the south ii Weakened oceanic conveyor belt shifted southward 1 Arctic latitudes deprived of warm waters like today c A meteorite impact darkened the sky and cooled the planet 7 Significant scientific interest in the causes and termination of the YD a The Earth System moved from a nearly full glacial state into a nearly full interglacial state in just three years i Extremely rapid recent climate change b Our current biosphere depends on the climate as it is c Role of anthropogenic activities i Deforestation ii Fossil fuel burning 8 The YD was 1300 years long and was the last significant glacial age 9 Since then our planet moved into the glacial minimum 10 Of Earth s climate shifted back into a glacial mode similar to the YD then within 100 years northern cities would be covered in ice 11 Scientific consensus that the onset and termination of the YD were very sudden a Ice core data indicate that the YD ended in 3 years b There is scientific debate as to the cause of the YD Biota 1 When did Homo sapiens first arrive in NA a Evolved from Austr 2 4 Ma b First evolved 150 Ka in Africa c By 30 Ka had expanded to Siberia d Crossed the Bering Straight 13 Ka 2 First Americans a Clovis People came from Siberia and colonized NA 300 years prior to the onset of the YD i Ancestors of all Native Americans b Excellent hunters used spears c Fossil evidence suggests the main animals present at that time were various ancestors of elephants mammoth and mastodon 3 Clovis hunters used fluted channeled spear points thrown by a hand held device that generated great velocity a Several lines of evidence show the great ability of these hunters spear points lodged in mammoth skulls vertebrae and ribs 4 A sudden extinction of large mammals occurred 12 9 Ka a 35 genera of large mammals disappeared from NA i All three American elephants ii Large beavers iii 5 species of horses iv NA camels v Giant ground sloths vi Giant armadillos b Three hypotheses i The overkill hypothesis human hunting may have led to a ME 1 Pros if animals weren t fearful of humans easy prey Clovis could have exhausted the supply of large prey in one area then moved on to the next 2 Cons just a few successive generations of early humans wiping out entire species of animals Accessibility of all of American with no horses or boats ii Climate change hypothesis species unable to adapt to the rapid climate change at the onset of YD 1 Pros climate change would have caused a change in the vegetation causing a demise in herbivore population which thus affected carnivores 2 Cons the species that died out at this time must have survived many similar climatic changes when ice sheets had waxed and waned throughout the Pleistocene iii Meteorite impact hypothesis new evidence suggests that the YD was a unique climatic event that may have been linked to a meteorite impact 1 Black layer of sediment in NA Europe dated 12 9 Ka contains rare materials likely of extraterrestrial origin 2 Pros cons still being compiled by proponents and opponents of this new theory Climate Change 1 Evidence from after 10 Ka climates 8 6 Ka a The hypsithermal interval was a long period of warmer than present i Warmest the climate has been since the end of the YD ii Based on fossil pollen data average global T was 2degrees C warmer than today b High heat during this time resulted in continental glaciers all but disappearing except Greenland and Antarctica c The glaciers have never