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Early Humans and Climate •Evolution & Extinction – Process of the rise and fall of species •Important moment in human evolution •4 mya: First hominids (our distant ancestor) •200 kya: Homo Sapiens (us) appear •12 kya: Human become farmers •200 years ago: Industrial Revolution begins – fossil fuel burning •Important events in recent climate history •30 mya: Global cooling begins (Himalayas forming) •2.75 mya: Enter ongoing Ice Age •8000 years ago: CO2 deviates from “normal” trend •6000 years ago: CH4 deviates from “normal” trend •Are these changes in Humans and Climate related? Almost certainly and in both directions. Evolution • “Remodeling not New Construction” • Natural Mechanism – Natural Selection – Survival of the Fittest, but who is the “fittest”? – Fitness is determined by environmental situation • Speciation – appearance of a new species – Species – group of organisms whose member can interbreed – Speciation usually caused by isolation of a small group in a region with different environmental stresses The Evolutionary Path to Humans 1 The Evolutionary Path to Humans 2 The Evolutionary Path to Humans 3 The Evolutionary Path to Humans 4 1 HOMO HABILIS ~ NICKNAME: Handyman LIVED: 2.4 to 1.6 mya HABITAT: Tropical Africa DIET: Omnivorous – nuts, seeds, tubers, fruits, some meat 2 HOMO SAPIEN ~ NICKNAME: Human LIVED: 200,000 years ago to present HABITAT:All DIET: Omnivorous - meat, vegetables, tubers, nuts, pizza, sushi 3 HOMO FLORESIENSIS ~ NICKNAME: Hobbit LIVED: 95,000 to 13,000 years ago HABITAT: Flores, Indonesia (tropical) DIET: Omnivorous - meat included pygmy stegodon, giant rat 4 HOMO ERECTUS ~ NICKNAME: Erectus LIVED: 1.8 million years to 100,000 years ago HABITAT: Tropical to temperate Africa, Asia, Europe DIET: Omnivorous - meat, tubers, fruits, nuts 5 PARANTHROPUS BOISEI ~ NICKNAME: Nutcracker man LIVED: 2.3 to 1.4 mya HABITAT: Tropical Africa DIET: Omnivorous - nuts, seeds, leaves, tubers, fruits, maybe some meat 6 HOMO HEIDELBERGENSIS ~ NICKNAME: Goliath LIVED: 700,000 to 300,000 years ago HABITAT: Temperate and tropical, Africa and Europe DIET: Omnivorous - meat, vegetables, tubers, nuts 7 HOMO NEANDERTHALENSIS ~ NICKNAME: Neanderthal LIVED: 250,000 to 30,000 years ago HABITAT: Europe and Western Asia DIET: Relied heavily on meat, such as bison, deer and musk ox The Evolutionary Path to Humans 5 Climate affects on human evolution Savanna Hypothesis • Cooling and drying of Africa started 30 mya • Forest shrink; by 4 mya this would reduce habitat for early humans • Humans fled to the savanna – Beginning walking upright, and free hands for other uses – Drives evolutionary changes, like larger brains Variable Selection Hypothesis • Early humans have been around since current Ice Age started • Subjected to many glacial/interglacial cycles • These numerous changes “forced” evolutionary changes • Problems: – Tropical Africa may have been little effect by glacial cycles – Monsoon rains continued in Africa throughout the changes in glacial cycles • Problem – Fossil evidence shows humans lived in many environments, not just savanna Bottomline – Human fossils are quite rare and tracking such linkages between human evolution and climate change is very challenging. Origin of Agriculture • 12 kya: A group of people stop being nomadic and learn to farm in the Golden Crescent • 10 kya: Domesticated animals and grains produced in China • What was happening at this time? – Melting of last major ice sheets – Monsoons very strong in the Middle East • Did climate “cause” humans to settle down? – 1) Monsoons for abundant resources so people did not have to “chase” their next meal, or look for water – 2) The Younger Dryas, back to cooler planet, may have made resources scarce and so people banded together to help each other survive Has climate change affected civilizations? Absolutely • Egypt – Culture peak about 5000 years ago, with decreasing monsoons the culture gave way to others • Mayans – 250 – 900 AD Yucatan Peninsula; AD 860 civilization came to an abrupt end – Lake sediments show this as a time of severe drought • Anasazi – 1300 BC to 1300 AD they flourished – But disappeared during time of extreme drought – Or possible, simply over used the available resources • Area was heavily deforested Example of Early Human Impact – Megafauna Extinction • Large mammals suffered a severe extinction 12,500 years ago. • Climate change? – just coming out of glacial period – But these same mammal species had survived numerous pervious glacial/interglacial transitions • In many regions around the world this extinction appears to coincide with human arrival Humans and PreIndustrial Climate Change: Ruddiman’s Hypothesis Early Anthropogenic Hypothesis: CO2 and CH4 are not following the same trend during this interglacial period as they have in the past. Hypothesis attributes this to human activities. Hypothesized Causes of GHG trends in the current interglacial period • GHGs peak about 7000 – 8000 years after glacial maximum (1/4 of precession cycle with influence from tilt cycle) – about 12 kya • CO2 – deviated from “normal” trend 8 kya – Humans deforested much of Europe – Burning and rotting trees add CO2 to atmosphere – Fewer trees left to remove CO2 from atmosphere • CH4 – deviated from “normal” trend 5 – 6 kya – Natural cause: decreasing monsoons, fewer wetland – Human cause: irrigation in Asia Problems with Ruddiman’s Hypothesis • CO2 rises are too large for the deforestation to account for • CH4 rises is at least partly naturally caused by reduced precession-cycle-driven monsoons Observation clearly show something different in occurring this interglacial – and human activity is one possible explanation Complex feedback effects in addition to deforestation and irrigation could be an answer