Geography M131

What era, period and epoch do humans live in?
-Cenozoic era(last 66 million years)
-Quaternary period (last 2 million years)
-Holocene epoch (Last 12,000 years; Before it was the Pleistocene (12k-2million yrs ago)
What are conventional modes of study and name types of human deposits for dating
Conventional:
-observation & experiment, documentation, (i.e. ports or the elfen trees), and palaeoecological recontstruction (fossils)
Human deposits:
-coins; artifacts
-eucalpytus pollen(came from Australian in 1800’s)
-bricks, tiles
Explain radiometric dating: Stable vs. radioactive; half-life; Where’s CS 137 come from? Lead? C14? CH4? What are they used for? And what are their limits? Whats BP?
Radiometric dating is a method of dating geological specimens by determining the proportions of particular radioactive isotopes present in a sample.
-Stable vs. radioactive Isotopes: (C12, 016/18) do not change after being form. Radioactive (C14,Pb 210, Cs 137) transform over time to new isotopes or elements ranging in time from seconds to millions of years.

-Half:life= time it takes for 1/2 of of your element o deta decay to a “daughter element”.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

-Cs137: only non-natural isotope; occured from atomic bomb tests.

-Lead 210: natural, decayed form of bedrock (radon) TAKES 22 YEARS TO DECAY! Ued for dating lake sediment, atmospheric lead rainwashed into lakes accumulates in layers mixing w/ natural lakebotton lead, as you go deeper into layers you can get down to where atmosphere has disappeared from 1/2 lives and there’s only natural Pb which you can then use as a base to determine age of other preceding layers.

-C14: very rare compared to C12(99%) and C13(~1%); Forms from N14 being hit by cosmic radiation and losing proton, eventually it will decay back to N14; Plants use CO2, take in C14 which decays but take more in to avg it out until it dies and then it begins to decline over time; If you compare dead plant w/ live one you can determine when it died; Can also measure it through humans because we continually eat plants until we die; C14 lasts w/in last 40-45,000 YEARS

-Methane (CH4), very common ancient sources(coal/natural gas) and also modern (BALTIMORE SEWAGE) ***Need more info***

-NOTE: BEFORE PRESENT (COINED BY LIBBY) refers to 1950.

What is incremental dating and how is it used? Explain dendrochonology? Layers of a tree? what do tree rings tell us? how to cross date?
-Time steps (daily, annual, decades, etc)
-Based on incremental growth(tree rings) segments or deposits (sediment).
-Used in dendrochronology: measure rings of trees that go dormant one season (Not tropical)
-LAYERS OF A TREE:
a) pith-center
b) xylem- inner, brings nutrients up from roots
c) Cambium- inner edge of phloem, cell factory.
d) phloem- right under bark, flows photosynthates down.

-Tree rings indicate climate: stressed trees=small rings
-Cross-dating: compare samples of dead tree to living one, line up rings to find age and extend chronology past the oldest living tree. (Can also be done for other item such as Peublo buildings)

What are the oldest trees in the world? Age? location? habitat? ring size?
-Bristle cone pines from California White Mountains are almost 5,000 years old.
-Live in very harsh dry slopey soil which has caused them to grow very slowly, tiny rings(bigger in wet years/seasons), very dense wood. (Trees that grow well every year have same size rings, called COMPLACENT)
-Can use cross-dating to get back over 8000 years
What is the relationship between dendro-dating and radiocarbon dating? Whats wrong with radiocarbon dating?
-Confirm one another by matching up years upto 3000 years ago (any sooner carbon is too young); THis allows you to correct C14 age to calender age (CALLED Calender year BP)
-uncertainties in radiocarbon: Large amount of CO2 released, increased cosmic rays and solar variability(Sun spots); ratio of C14 to C12 is not stable all the time so use tree rings to recalibrate errors.
How to use glacial ice for dating? Age? What does it show?
-incremental dating
-core down several km of ice that contain lil bubbles w/ samples of atmosphere.
-range from 100,000 years(greenland) to 650,000(Antarctica).
-Shows summer(light) & winter(dark layers); differences in snow properties (density & deposition rate) and atmosphere of the times.
What are varves and how are they formed? What do they indicate? What are warm lake varves? how are THEY formed? And what are deep ocean varves? Formed? -WHAT DO ALL VARVES HAVE IN COMMON?
-Varves: annual layers formed in lake or marine(rare) sediment through patterns of deposition.
-Found in glacial bodies of water- moves a lot of coarse sediment int lake during summer during melt, stops in winter and lakes freeze over stopping any further deposition besides the fine clays drifting in water that form a thin dark layer.
-indicate years of lots of melt forming large layers of mineral matter, giving ideas of past hydrology of lake.
-Form in places farm from glaciers caused by lots of biological activity and vigorous precipitation of Calicum Carbonate and runoff of sand in winds/precipitation(All coming in summer- form light layer); Winter covers lake in snow so no biological productivity, shielded from outside depositing, forming dark thin layer of fine clay.
-Deep ocean: (Found in Santa Barbara) formed from productivity changes w/ summer and winter and season precipitations fluctuating.
-ALL VARVES HAVE IN COMMON:
a) bottom waters un-oxygenated (No organisms destroying the layers/patterns), also layers are very delicate & require dry ice supercooling.
How to measure & calibrate Lichenometric dating? Whats Lichen Thalli?
-Lichen Thalli= lichen growing radially outwards over time from microscope to visible size.
-Use on landslides; if small thalli then recent, if large then older(used a lot in England/Europe)
-Calibrated through cemetary tombstones, see age & measure size of thalli
Radiocarbon limits and problems? how are they “fixed” for the future measurements?
-limited by half-life
-can’t be used in recent dating because of human activity; last 200 years of Industrial revolution pumping fossil fuels into atmosphere full of “Dead” CO2 w/ decreased C14; Plants today getting less C14.
-Problem “fixed” through atmoic bomb testing releasing extra C14 in air, any plant living 1965 or after will be enriched in C14 to help date plants of distant future.
Why are peat bogs such good sites for sampling? What do they tell us?
-form stratified deposits of moss
-go back 25-40k years
-so much peat that it removes top ecosystem from contact w/ water table or soil nutrients so we can see things deposited ONLY by atmosphere
-Peat is wet & acided so decomposition is VERY SLOW, good preservation, once peat builds up becomes anoxic.
-Tell us: about environment at site, vegetation, productivity, leaves/fossil pollen/organisms.
How do you use lake sediment to determine past?
-Lots of things settle on lake bottom and become preserved, allows you to reconstruct environment near lake (Pollen, organisms) and far away brought in from wind.
How to determine environment from archeological remains
-discarded shells, food, etc.
-forms stratified deposit
-floors in whcih people live form stratified deposits.
What is Palynology? How is it used? Why are they good sources of studying and what are the 3 source locations that end up in lake
-Study of pollen
-reconstruct vegetation in area
-By reconstructing vegetation you can THEREFORE reconstruct climate.
-EX. Holly/Ivy/Mistletoe- require different level of warmth (From right to left in order), when one or more not present then you know temperature.

-Pollen grains are distinct to plant genus/species
-Many get deposited easily and A LOT, particulary wind pollination ones.
-Good preservation
-Sources into lake:
1) from living environment around lake
2) runoff from watershed
3) wind dispersal

What are diatoms? Why are they VERY useful in dating and determining factors? Whats the trade-off for studying them? Whats an example of how they’re used?
-uni-cellular algae w/ siliceous shell(that green scum in your garden pond)
-REASONS THEY ARE GOOD SPECIMEN:
1) Very tiny, float in air and quickly colonize open water
2) Good diagnostic of Water Conditions*** responsive to water conditions(ph, salinity, nutrient content, temp)
3) Taxonomically distinctive
4)Preserve well in sediment
5)Really abundant in lakes & streams

-Trade-off: When you process for pollen you destroy diatoms and vise versa; must be done separately.

-An example: Used to analyze pH in 1980’s in correlation to Acid rain from burning of coal.

What is Prof. Macdonalds FAVORITE BOOK?
-P.V. Glob, THE BOG PEOPLE; Iron-age Man.
It’s about NW European bog communities that sacrificed people and were well preserved.
What is Packrat midden? WHere are they found? and how is it used?
-Important to SW deserts of US.
-Rats nest in crevices/protected areas out of element and pull in a lot of “Stuff”. They urinate on them and it dries and hardens w/ plant material forming “Amber Rat”. LASTS BEYOND RADIO-CARBON DATING( up to 40,000 years).
-People collect the “amber rat” and dissolve in warm water to take out plant remains which are gathered close to nests and indicate vegation.
-Can combine many to indicate large environment, shows low altitudinal levels of trees in past.
What is glacial Till?
Un-stratified deposits composed of large rocks, gravel, sand, silt and clay
-IF LACKS ORGANIC MATERIAL THEN INDICATES GLACIAL ICE.
What are Cirques and Aretes? What do they indicate?
-Cirques are round amphitheater shaped head found at the top of a glaciated alpine valley. Tell us that sometime in the past and enough snow for alpine glaciers, but too warm today
-Aretes are An arete is a thin, almost knife-like, ridge of rock which is typically formed when two glaciers erode parallel U-shaped valleys. The arete is a thin ridge of rock that is left separating the two valleys.
How do you use Sand dunes and Luminescence dating?
For Sand Dunes:
i. To have sand dunes form and active you need:
1. Dry/arid conditions enough for sand to be mobile and no vegetation to hold in place.
2. Wind to move sand/shape dunes, orient of dunes indicates dominate direction.
3. Supply of Sand
ii. Tells us- ex. In Alberta- change in direction from today and much less water in region.

For iii. Luminescence Dating: when sand is active and blowing around it is exposed to sunlight, bleaching out natural activity that they would have when buried. When buried they pick up the ambient radioactive activity from minerals around them. When exposed to light they will release that energy as light luminescence to gauge how long it has been buried. So now not only can we see dry conditions of the past but also when they STOPPED being active and remained buried.

When was the LGM? What did Earth look like? (Australia? Alaska?) What were the names of the sheets and were were they located? How low did sea level drop? What was going on in the high elevations away from N. Hemisphere? Overall Vegetation change?
-Last Glacial Maximum: 20,000 years B.P.
-N. Hemisphere (N. America, Greenland, N. Europe & Central Asia had MUCH more ice)
-CORDILLERAN Sheet: Covered Coastal mtns of E. Alaska down to BC Canada into Washington/idaho/montana
-Laurentide Ice Sheet: THICKEST ICE, made up of atleast 2 or more DOMES; Extends from Rockies to New England, south of Chicago and north merging w/ Greenland Ice Sheet.
-Greenland Ice Sheet: Self-explanatory
-Fennoscandain Ice Sheet(European): Ireland across germany, france, Poland, covering baltic republics, N. Russia, all the way to Urals; Scandanavian countries completely covered.
-Lots of Sea Ice! Even in summer, may have linked N. America to W. Europe.
-Australia joined w/ Tazmania & New Guinea
-Alaska and Russia connected by BERINGIA making Asia & America a Super-continent. NO ICE COVER IN ALASKA (Too dry), evidence of people/mammals there.
-Sea level drops 80-120 METERS
-In S. Hemisphere: Some glacial evidence in mountain peaks (Africa, Andes, New Guinea); All vegetation zones moved down (1500 Meter shift!- seen in Rat Amber in SW)
-Holocene WARMING caused a 1KM shift back up*
-Overall vegetation: decrease in forests, expansion of treeless(desert, extreme desert, grasslands); Some parts too cold, some too dry; drop of tropics(over 50%) and increase in drylands (almost 3x)
What happened to the Southwest during the Pleistocene? Glacial moraines? Pluvial? Plaia? La Brea Tar Pits?
-Sea level dropped, expansion of CA coastline, particularly near SF; some offshore islands may have been connected to mainland.
-BIG buildup up of glacial ice in Sierra’s, filled Yosemite
-Glacial MORAINES- east coast of Sierras formed them from glacial till that form on edges or front of glacier from material deposits after ice retreats (SHows where glaciers ends)
-“PLUVIAL” Lakes formed; period of time where we have wet/cooler conditions and LOTS OF LAKES- Death Valley, Owns, Salton Sea, LOTS MORE WATER(Different from other parts of Earth); MASSIVE LAKE in what is now Salt Lake City, LAHONTAN PLUVIAL LAKE NEAR RENO.
-When lakes dried formed PLAIA,extremely flat smooth terrain w/ mineral deposits(geologic lake beds)
-Tar Pits: Show hollywood hills (preserved)flora and fauna not not stratified so need to radiocarbon date; Hollywood hills looked like Bay area(redwood/oak/lush), Mega Fauna diverse indicating mixture of ecosystems; CA was much more forested than it is today.
What lasts longer COLiD or WARM? What causes the shifts? What are the initial 4 glacial periods called? Their problems?
-Initially thought 4 glacial episdes: Nebraska, Kansasian, Illinoian, Wisconsin(LGM)
-Problems: Glacier advances and deposits AND erodes material then retreats, when another glacier advances erodes/deposits it covers previous one; However you want constant deposition without erosion to see real stratification. This can be seen in OCEAN BASINS which throw out 4-glacier theory.
What are foraminifera and how did they show the real Glaciations? (Hint: Oxygen isotopes) And how many glaciations did they determine there were? What is the alternative method of O16 measuring that backs up this theory?
-Foraminifera: Plankton that make shells out of oxygen in water; has same concentration as the ratio of 016/018 in water.
-O16 lighter and will evaporate faster than O18; O16 evaporates from water and precipitats back into ocean maintaining an equilibrium however if glaciated, evaporated O16 will precipitate and get tied up in ice sheets instead of flowing back increasing concentration of 018. THEREFORE, more O18 to O16 means larger the ice sheets, and as O16 increases ice sheets are melting and returning water to oceans.
-This is databased in the shells of foraminifera and stratified in ocean sediment.
-A few meters of sediment can show millions of years of deposition.
-NEW ESTIMATES DETERMINED THERE WAS 17 GLACIATIONS SEEN THROUGH THE O16 THEORY.
-Ice core sediments: High O16 means cold weather and vise versa; backs up ocean sediment theory (Only goes back between 150-650k)
Was Earth ever as warm as today? What is different about modern times? What’s been going on the last 2 million years? What has been changing with amplitude and frequency of changes? For MARINE ISOTOPE STAGES(MIS) what do odd and even numbers indicate?
-Around 140,000 years ago earth was as warm as today
-We are in an unusually warm time compared to last 1 million years.
-LGM was ~170,000 years ago
-Most of the time earth is between extremes.
-3 Million years ago earth was warmer than today, very little glacial ice (Seen in O16 ratio).
-A lot more extreme/pronounced shits recently in climate; The amplitude has been in increasing between shifts in last 1 million years, but the frequency between shifts has become longer.
-CLIMATE IS UNSTABLE, NOT GOING TO ESCAPE CLIMATE CHANGE.
-MIS: Numbers at peak of extreme climates; Even=glaciation & Odd=interglacial.
What is Paleo-magnetism and how is it used? Whats Matchuyama?
-Magnetic polarity of earth reverses
-As mineral matter is floating down into ocean and IF its sensitive to magnetism it will orient itself toward poles and pile up on ocean floor in that direction. If there’s a shift the material will shift 180 degrees from previously stratified layer.
-Matchuyama is the first reversal seen in sediment cores from 800,000 years ago.
What defines the Quaternary Period? How do we know when Ice Sheets first began to build up? when were temps cool enough? Why did this occur?
-Evidence: Icebergs: come off in big chunks from glacier points called FYORDS and float into oceans; They contain GLACIAL TILL which drop into ocean as they melt, this material is much larger than natural accumulation in deep seas, only explanation for the transportation of such large rocks (DROP STONES).
-FIRST DROP STONES SEEN 2-2.5 Millin years ago; indicate iceasheets forming.
-ICE SHEETS FORMED FROM CONTINENTAL DRIFT: Antarctica breaks off from Gondwandaland(allows circulation between continents), moves into southern pole and begins accumulating ice; SAME HAPPENS IN N. Hemisphere- Laurasia drifting north however NO LAND AT NORTH POLE! But there are land masses ~70 degrees to accumulate ice.
Define/Explina the three reasons of CROLL(define) that explain climate patterns and Glaciation and the period of time for their cycles. Does this effect the amount of energy recieved from sun? If not then why does it get cold enough for Ice age? Whats the positive feedback effect? How does it effect ice ages and warming?
Croll(19th century theorist)- MILUTIN MILANKANOVITCH: See earth as behaving like a Top/dradle, moves around it’s axis; Similar characteristics of eccentric/non-eccentric, pulled by gravity, etc.

-ECCENTRICITY: Earths orbit not a perfect circle sometimes its PERIHELION(when earth is closer to the sun) and APHELION (when earth is further away) CHANGE FROM VERY ECCENTRIC ORBIT TO MORE CENTERED OCCURS IN 100,000 YEAR CYCLE

-OBLIQUITY:The Variation of the tilt of Earth; Tilt of Earth’s access(23 degrees) and not the distance from sun dictates the seasons. THE MORE THE TILT THE MORE EXTREME THE SEASONS(wabbles between 21.5 and 24.5 degrees); IT IS ON A 41,000 YR CYCLE.

Precession- Switch of Perihelion & Aphelion in N/S Hemisphere timing; Perihelion will change w/ obliquity causing it to form in summer; Winter in July & Summer in December; CYCLE IS EVERY 23,000 YRS.

-DOES NOT EFFECT TOTAL AMOUNT OF ENERGY RECIEVED FROM THE SUN; Winter temps don’t matter SUMMER TEMPERATURES MATTER, IF NOT ENOUGH HEAT IN SUMMER TO MELT SNOW IT BEGINS TO ACCUMULATE.
-IF YOU LINE UP ECCENTRICITY/OBLIQUITY/PRECESSION YOU CAN PREDICT AN ICE AGE.
-Ice age creates positive feedbacks through INCREASED ALBEDO(WHite snow reflects more light back to space promoting more cooling and more snow THEREFOR more albedo!
-Where as with warming, typically warm conditions occur after peak of insulation is decling because glacial ice takes time to melt, removing more and more albedo.
***Insolation is the solar radiation that reaches the earth’s surface.Insolation affects temperature. The more the insolation, the higher the temperature.In any given day, the strongest insolation is received at noon. The longer the duration of sunlight the more insolation recieved.

Holocene and into the future: Where are we at on insolation & when is the next ice age?
-We maxed out at 9-15kya in insolation and are passed it, started to slide down at end of LGM heading into another ice age
-Estimated next ice age is 30-50 kya, we’re headed into cooler conditions.
4 principle approaches dating techniques
historical records
incremental dating
paleomagnetism
radiometric