1Geography 1001:Climate & VegetationInstructor: Andrés Holz• Final review session:– Sat at 10:30amLecture 27: Thursday Dec 13500 million years ago.. 400 million years ago..300 million years ago.. 200 million years ago..2100 million years ago.. 50 million years ago..1 million year ago..Less than a million year ago..•So far, we know that the Earth has experienced at least 8 ice ages•Last one? Today•If we think of the earth life being a calendar year (i.e. from Jan 1 to Dec 31), when do you think we appeared?Continents and humans• Which on is true? Continents have been ________ since _______, and humans arrived during the very ______ of earth history.– Dynamic, earth creation, “last second”– Static, human creation, “last month”– Dynamic, atmosphere creation, “last second”– Static, ocean creation, “last second”3But how have the conditions for life changed over these 4 billion years?The solar system form ~4.6 billion years ago.4 billion years ago, the atmosphere was made off of volcanic emissions• TIME– 4 billion yrs ago • PROCESS– Water vapor– Ammonia (NH3)– Methane (CH4)– Hydrogen sulfide (H2S)– Hydrogen gas (H2)– Carbon monoxide (CO)– **Very little O2& N2All water was held in the atmosphere as vapor because of high temperatures (water vapor in high clouds greenhouse effect). • TIME– 4 billion yrs ago – 3.1-3.5 billion yrs ago • PROCESS– Water vapor, CO, (N) dominant. – O2begins to accumulate.How?– Water vapor clouds common in the lower atmosphere (albedo forcing clouds).– Cooling of the atmosphere causes precipitation and the development of the oceans.– Break of H2O by ultraviolet rays H2O  O2+ H – First single cell algae & bacteriaAtmosphere• The two atmospheric components that are very common today, but were very scarce 4 billion years ago are – Nitrogen & Oxygen– Hydrogen & Argon– Oxygen & CO2– Hydrogen & Nitrogen Oceans• Primitive oceans formed around 3.1-3.5 billion years ago, mostly because of – Warming of the atmosphere– Extraterrestrial rain– Cooling of the atmosphere– Glacier melting• TIME– 3.1-3.5 billion yrs ago • PROCESS– Anaerobic respiration• Single cells algae were able to – produce Energy without O2– Take C-H20 (simple organic molecules food)& break down intoCO2+ alcoholsenergyFor ~800 millions of years, CO2 was released (as by-products of respiration) & built up in the atmosphere and oceansThere was enough CO2 in the atmosphere to sustain life….4• TIME– 2.3 billion yrs ago….• PROCESS– PhotosynthesisSingle-cells (blue-green algae have chlorophyll)CO2 + H2O CH2O + O2 built up–Initially, the released O2was lethal to the living organismsenergysunlightfoodAtmospheric changes• The take home message here is that– Life on earth is a response to the environmental conditions– The environmental conditions is a response to life development– Life and the environmental conditions are both triggers and responses to each other – None of the above• TIME– 1.9 billion yrs ago….• PROCESS– Ozone (O3) layer is being built in the stratosphereFilters out the UV radiation making life possible on land development of O2tolerant organisms• TIME– 1.3 billion yrs ago….• PROCESS– Aerobic respirationCH2O + O2CO2+ H2Oenergy• TIME– 600 mill yrs ago….• PROCESS– Life is widespread in the oceans• Single cells• Early fishes• Large algae5• TIME– 420 mill yrs ago….• PROCESS– Life is widespread on lands• Earliest plants• Invertebrates• Vertebrates• TIME– 350 mill yrs ago….• PROCESS– Development of tropical rainforest• fossil fuel  today’s oil• TIME– 200 mill yrs ago….• PROCESS– Colonization of larger vertebratesLife expansion• The main reasons that explain the expansion of life on the continents are– Increase of sulfur in sea water via high volcanic eruptions– Decrease in the sea-level due to high temperatures – Creation of Ozone layer that blocks UV rays – All of the aboveOne of those (smaller) vertebrates were our ancestors: a bit of ourselves..Hu—wo—mans • Genetically speaking, we are more similar to ________ (by 1%) than to_________(by 1.5%).– Chimpanzee, Bonobo– Gorillas, Chimpanzee– Bonobo, Chimpanzee– Gorilla, Bonobo6How we have modified our environment at various scales?Broad Expansion of Human Habitat(we took over spatially!) Remember that 18,000 BP, the Earth looked like this map from Earth and Life Through TimeIce & cold desserts steppessavannas ForestsFood Web-Land Animals (we also took over new niches)Traditional modification of our environment at local scale• It took us all human history to reach 1 billion, close to a century to reach 2 billions (1930), 30 years to reach the 3rdbillion, 15 yrs for the 4th, 12 yrs for the 5th& 13rs for the 6th7Population• The most dramatic increase in population during earth history occurred– During the last century– During the mid to late 1800s– During the first half of the XX century– During the first half of the XIX centuryYear1940 1960 1980 2000 2020 2040 2060Population (in thounsands)02x1064x1066x1068x10610x10612x10614x106WorldConstant rate Developed Regions Less Dev RegionsLeast Dev Countries UN World Population Prospects (2006)UN World Population Prospects (2006)• A this rate, it was predicted that it would take only ~770 years to increase to the point where there were 10 human beings for each square meter of ice free land on the planet!• Is there any problem with that?Population collapse predictions• Malthus predictions were related to _______ triggered by ______, yet failed because of ___. – population collapse, climate change, technology & market economy– population collapse, lack of food supply, technology & market economy– population trends, climate change, little ice age– Population growth, biodiversity loss, species introduction– None of the above Yet, Malthus (& his opponent) didn’t see the current • Biodiversity loss– Habitat fragmentation– Species introduction (that are taking new niches)– Over hunting– Greenhouse gases • Could these changes be relevant for our future?• Does earth experience natural changes?Earlier civilizations• Two examples of “sophisticated”civilizations that kept their population under control in order to cope with their resource availability were:– Inuits and Aztexs– South