geol exam 2
6. List a way age can be determined in a geologic sequence.
"Index" fossils is the best for age determination. Species existed for a relatively short period of geologic time and found over large geographic areas are the best
What proxies were used and what can these tell us about climate?
*Proxies= indirect indicators, clues, the data analyzed Paleomagnetic reversal data, fossils data, correlating ash events, and radiometric dating.
What is meant by "polar amplification? What could account for the greater relative warming in the polar regions in the Cretaceous compared to today?
-More relative warming in the polar regions. -Maybe because of feedbacks (ice-albedo) and/or differences in ocean circulation
What are foraminifera (i.e. foram)? What is the difference between benthic vs planktic? What is the composition of their shells?
-Single celled protists with CaCO3 shell (little fossils in the ocean) -Planktic live near surface -Benthic live near the seafloor ---Warmer water shells use O16 colder uses O18
15. In what ways is the PETM similar to climate change today?
-The amount of CH4 and CO2 released to the ocean-atm system during the PETM is similar to the predicted total amount being put into the atmosphere between 1870 (industrial revolution) and the year 2400. -This assumes fossil-fuel emission continue unabated and carbon-sequestration remain at current levels. The warming today is due to humans unlike PETM
What are the processes that are important in the long term carbon cycle? Note long term = 10s to 100s of millions of years = the same timescale where changes in plate tectonics and weathering become important. Which long-term processes add CO2 to the atm and which take it away?
1. Volcanic Outgassing -->Control of atm CO2 by Variation in Sea Floor Spreading & other Volcanism 2. Uplift-Weathering-->Control of atm CO2 by Tectonic Uplift and Subsequent Chemical Weathering of Mountains
When was the Cretaceous?
140 to 66 million years ago
How cold is the deep ocean today? How cold was it during the warmest part of the early Cenozoic Greenhouse time?
17 degrees Celsius (62.6 degrees Fahrenheit) - Cenozoic. Is this true?? -->this simply cannot be true.Google says -3 C: i think the first number is for the Cenozoic Greenhouse time not modern day. Today - Little less than 0 C Cenozoic - 17 degrees C, around 60's F
9. When did the atmosphere become oxygenated? How did this happen?
2 billion years ago because plants were growing and photosynthesizing the co2
What is the CO2 level now?
400 ppm
What is the expected range for future CO2 values (year 2100)?
500-1000 ppm
14. How was the PETM a threshold event?
A stability threshold was crossed which set into motion: (a) rapid-destabilization of shallowly buried methane hydrate (CH4) deposits along continental margins, and (b) oxidation [i.e., weathering] of organic carbon (C + O2CO2) that was buried in permafrost, and was released as Antarctic(?) permafrost melted.
16. Be able to determine the numerical age of a material given the half-life of that Parent-Daughter decay series, and information on the percent of parent remaining or on the parent daughter ratio.
Age= # of half lives X half life 1:1 = 1 half live 1:3 ratio = 2 half lives 1:7 ratio = 3 half lives Parent always starts at 100%, daughter starts at 0%, every 25% increase/decrease = 1 half life
How does fractionation of oxygen isotopes in the hydrologic cycle affect the values of stable oxygen isotopes in the ocean?
As global volume ice sheets increases, the relative abundance of O16 in the ocean will go down, and the relative abundance of O18 in the ocean will go up (reverse for ice sheets that decrease).
What are the 3 big misconceptions about climate change that we addressed with this unit? Explain why each is incorrect, and what we should be thinking instead (the correct conception, rather than the misconception).
Because CO2 and temperatures were higher in the past, we don't need to be concerned with global warming today. Because CO2 and temperatures were higher in the past, humans can't be the cause of global warming today. CO2 and global average temperatures have never been higher than today.
3. See the reading: Owens Lake climate archive and proxies - a case study: Why did they core in the lake bed rather than just examine the land outcrops around the lake and in the mountains?
Because the layers of the lake bed contain sediments, soil, and other material that have built up over millions of years. They help indicate the temperature in the past, a large volcanic eruption, and much more.
When was the PETM? What was the background temperature doing before and after this event?
Between 52 and 55.5 million yrs ago The Earth was gradually getting warmer. However once the methane hydrate deposits were slowly melting, they suddenly released the Methane gasses trapped in the ice, which rapidly warmed the Earth.
11. Are ash-fall (tephra) events global or regional?
Both!
5. How did atmospheric CO2 levels change from the early to late Cenozoic?
CO2 level increased drastically,
4. How were continental weathering rates changing from the early to late Cenozoic? What landmass in particular was being so highly weathered and why? How did this influence the transition from a Greenhouse to Icehouse World?
Continental weathering rates increased (Maybe) The india + Asia combining of continents allowed for new mountains that were weathered It influenced it by taking CO2 out of the atmosphere quicker and speeding up the process of transitioning to an icehouse world
When were the icehouse times during the last 600 million years (= Phanerozoic Eon)?
Early 400 millions years ago, early 300, mid 200 and the last 25 million years
3. What impact should this level of luminosity have had on the surface temperature of the Earth if the Earth had the same Greenhouse effect as today? If the Earth had no Greenhouse effect? Be able to infer this information from diagrams shown in class.
Early earth had a weaker solar radiation and a stronger greenhouse effect. If the earth back then had the same greenhouse as we do today, the surface temperatures would be lower.
Describe how atmospheric CO2 can be controlled by Volcanic Outgassing (sea floor spreading and other volcanism).
Fast spreading-- quick input of CO2 whereas slow=slow if there is a super continent it is more likely to break up and therefore produce higher SFS rates.
8. Why are patterns and events in fossils, paleomagnetic polarity data, geochemical data useful for determining age? How are they helpful in correlating layered sediment or ice from different locations?
Fossils-(pattern of life: different forms of life lived at different times; extinction events) Paleomagnetic polarity data -("bar code" of time with global reversal events) Geochemical data- (e.g., oxygen isotope cycles) that are tied to astronomical cycles[used in sediment, ice,and coral archives]
5. How might the faint young Sun paradox be solved? Discuss geothermal heat flux (volcanic outgassing), albedo, and super greenhouse conditions.
Geothermal Heat = heat generated from the radioactive decay of unstable isotopes in Earth's interior. Not enough to make up for a needed 70 W/m2 of solar heat but maybe enough to keep the ocean from freezing Lower albedo (due to more water covering the planet) = more solar heat absorbed Not low enough on its own to counter the effects of the faint young sun Super Greenhouse conditions Early Earth = weaker solar radiation, stronger greenhouse, more CO2 in atmosphere Compare to stronger solar radiation and a weaker greenhouse
Was this an icehouse or greenhouse time?
Greenhouse
Would CO2 be higher in Greenhouse or Icehouse worlds?
Greenhouse
What were the CO2 levels in Icehouse times? Greenhouse times?
Greenhouse= greater than 1000ppm Icehouse=below 1000ppm
Pay special attention to question in the exercise that put modern warming into a longer term context (e.g., have humans ever experienced in the past CO2 level that are predicted for the near future?; has Earth ever experienced higher CO2 levels that what is predicted for the near future?)
Humans have never experienced co2 levels that are predicted for the near future, Earth has experienced co2 levels similar to what is projected for the near future.
What are the differences between Icehouse and Greenhouse worlds?
Icehouse: more or less extensive glaciation, less CO2 in atmosphere Greenhouse: no ice anywhere on the world, more CO2 in atmosphere
What could have caused a hiatus in the record (i.e., to cause part of the record to be missing)?
If the water dried up, the wind could have removed the sediments that used to be there.
When and how did human activity affect the local climate of Owen's lake region?
In the early 1900s there was an aqueduct (the Los angeles Aqueduct) created
What are isotopes? Stable isotopes vs unstable isotopes?
Isotopes: different # of neutrons, same # protons Stable: not radioactive (will not decay) (daughter isotope) Unstable: radioactive (parent isotope)
13. What are isotopes? Stable vs unstable isotope? Parent vs daughter isotopes?
Isotopes:atoms of the same element with the same number of protons, but a different number of neutrons Parent: unstable Daughter: stable
15. How is the numerical age of a material determined using radioactive decay of unstable isotopes? What assumption needs to be made?
It needs to be assumed that the unstable isotopes (parents) are 100% present when the rock was formed and 0% of the stable isotope(daughter). Age= # of half lives X half life(specific to that pair)
19. Using the PETM as an analogy, how long would we expect it to take for atmospheric greenhouse gas levels in the future to return to pre-industrial (pre-fossil fuel use) levels? How many generations would pass before silicate weathering would return greenhouse gases in the atmosphere to a pre-industrial level?
It took roughly 150,000 years for the earth to go back to pre-PETM temperatures, so we could expect that it would be about the same for our climate today. It would take about 6000 generations before silicate weathering would return greenhouse gases in the atmosphere to a pre industrial level. However, this number is just a guess - 150,000 years might be too short of a time period to undo the damage that we have done.
16. How was the PETM different than the warming today?
It was different from the warming today because it was already taking place during a greenhouse time period, but the causes were not man - made like they are today. It was most likely triggered by volcanoes, slight fluctuations in earth's planet, etc that eventually crossed the threshold.. It was a gradual and then all at once process, and today the warming of our climate is happening much faster.
2. Compare and contrast these archives: lake sediment, speleothems (cave records), ice, corals, tree rings, sedimentary rocks, and marine (sub seafloor) sediments. Which are useful for recording events of the recent past vs far past? Would any of these have geographic restrictions (e.g., are primarily restricted to recording data from certain places)? 47h
Lake Sediment: 1- 10^9, use mainly 1-100,000 yrs Speleothems: cave deposits. Thicker stalagmites/tites signify a period of high precipitation while thin stalagmites suggest a period of drought Ice: 1- 1,000,000 yrs, use mainly between 1-10,000 yrs Corals: 1-1,000,000 yrs, use mainly between 1yr-1,000yrs Tree Rings: 1-10,000 yrs , use mainly between 1-1,000 yrs Sedimentary Rocks: 1,000 yrs - 10^9 yrs Marine Sediments: 1- 10^ yrs, use mainly between 1,000-10 ^8 yrs
1. How are layers in ice, corals, trees, cave deposits and sediments/sedimentary rock like pages in a diary?
Layers build up in these archives with age. Therefore, the amount of layers helps indicate how young or old certain material is.
Could weathering of silicate rocks be a quick "fix" for global warming today? Explain your reasoning.
No because it is in the long run carbon cycle
4. According to the sedimentary rock and fossil records, was the early Earth frozen, as astrophysics models predict or not?
No it was not frozen.
1. Based on the handout did the N and S hemispheres transition to the current icehouse time simultaneously?
No, S hemisphere cooled faster than N hemisphere
10. What is meant by normal vs reverse polarity? Are changes in Earth's polarity a global or regional event? What is the global polarity time scale? How is the inclination data useful in determining age? Be able to apply this like in the homework
Normal polarity is where the magnetic north points (roughly) towards the geographic north pole. This is how the magnetic field is aligned today. Reversed polarity is in the opposite direction, and the north end of the magnetic field is close to the present-day south pole. It's a Global event. The Geomagnetic Polarity Time Scale (GPTS) has been constructed from an analysis of magnetic anomalies measured over the ocean basins and tying these anomalies to known and dated magnetic polarity reversals found on land.
How are oxygen isotopes ratios measured? What unit is the data expressed in? How is this calculated?
O18 & O16 Calculated by neutrons The delta values are expressed in units of "parts per thousands" or "per mil"
14. What is half-life? Do all parent-daughter isotope pairs have the same half-life duration?
One half-life is the time it takes for ½ of the parent isotopes present in a rock or bone or shell to decay to daughter isotopes; has to decay by ½ Each pair has their own unique half - life duration EX. Carbon-14 and Nitrogen -14 : 5,780 yrs half life duration
13. Explain the leading hypothesis for the cause of the PETM.
PETM was a major and rapid change to the carbon cycle that released a lot of stored organic carbon to the ocean-atm system.
12. What is permafrost? Where is it today? Where might it have been before the PETM?
Permafrost: a thick subsurface layer of soil that remains frozen throughout the year, Corresponding climate-ecosystem-soil simulations accounting for rising concentrations of background greenhouse gases and orbital forcing show that the magnitude and timing of the PETM and subsequent hyperthermals can be explained by the orbitally triggered decomposition of soil organic carbon in circum-Arctic and Antarctic terrestrial permafrost. -There was no permafrost in very early Cenozoic because it was greenhouse there was a release from previous permafrost though.
4. What are proxies? Why is a multiproxy approach desirable in deciphering history of climate change?
Proxies are indirect indicators, clues, the data analyzed. A multiproxy approach is desirable because proxies are limited to location and therefore multiple proxies are important for the understanding of a global climate change.
8. Characterize the Paleocene-Eocene Thermo Maximum (PETM) in term of temperature change and rate of warming, rate of recovery, isotopic changes (oxygen and carbon [carbon isotope excursion: CIE]), biological events in the ocean and on land.
Rapid (1000-10,000yrs) warming of 6 degrees C in the deep ocean and gradual (150,000 yrs.) return prior conditions.
10. Why is δ13C data so important for determining the cause of the PETM?
Sample=Benthic foraminifera shells are being measured because their shells record C13/C12 ratio of the water from which they are participated
3. How were seafloor spreading rates changing from the early to late Cenozoic? How did this influence the transition from a Greenhouse to Icehouse World?
Slower rates of seafloor spreading + increased rates of continental weathering → CO2 decreased + gradual opening of Tasmanian-Antarctic ocean gateway helped cool Antarctica → pushed Antarctica past a climate THRESHOLD → ICE SHEETS grew rapidly → Icehouse state started
2. What is meant by a climate "threshold" or tipping point?
Small gradual perturbations (changes) can rapidly shift the state of the system
5. Why is it important to determine the age of a sequence sediments (or rock or ice etc)?
So we can look at the chemicals, minerals, and fossils in said sediments and learn what the climate, atmosphere, and conditions were during that time. Knowing this gives us insight into our own climate and can help us predict and prepare for the future.
11. Describe modern methane hydrates: what are they? What do they look like? What unique properties do they have? where are they found? Under what conditions are they stable? How do these become unstable? Is there any energy (economic) potential to recovering these? How do gas hydrates potentially impact climate? Methane Hydrates:
Source: bacterial waste from decomposing organic matter Stable: under high pressures & cold temperatures. Where: In the seafloor under the continental slopes and in permafrost regions Climate Impact: Huge amounts of methane are stored around the world in the sea floor in the form of solid methane hydrates. These hydrates represent a large energy reserve for humanity. Climate warming, however, could cause the hydrates to destabilize. The methane, a potent greenhouse gas, would escape unused into the atmosphere and could even accelerate climate change.
. Explain how CO2 can be removed from the atmosphere over millions to billions of years by chemical weathering of the continents. How does this help explain why the Earth doesn't still have a Super Greenhouse atmosphere?
The chemical weathering of the continents created more surface area on land, which lead to more absorption of co2 from the earth. This helped lower the global temperature gradually, which means the earth could eventually be an icehouse world again.
Before humans affected climate was it steady and stable or changing - how did it change for the last 800,000 yrs?→
The lake level was changing -- grain size was changing, pebbles and the color Reddish color of sediment tells us it was low-level oxygen in the deep lake; the ashy Sediments tell us there was a volcanic eruption. → looking at pebble types (look at chart types) → hiatus? If water dried up, the wind could have removed the sediments that used to be there (ie, salt is removed from the records)
What is the timespan of the Cenozoic Era?
The last 66 million years
6. Characterize the early Earth (4-3.5 billion years ago) in terms of heat flux, solar radiation, life, atmospheric composition, distribution of oceans and continents.
The solar radiation was weaker. 3 bil years ago was the earliest photosynthetic bacteria. 2.2 bill years ago was when there was the first green algae. 1. High Heat 2. Low Albedo 3. Lots of greenhouse gases 4. Mostly oceans
18. What are the steps in the chemical weathering feedback? Is it a positive or negative feedback?
The steps in chemical weathering feedback are: if something causes climate to get warmer, then there is more vegetation, higher temperatures, more chemical weathering → which then removes the CO2 from atmosphere that was causing the cycle in the first place. This is a negative feedback.
Life cycle of Sun and where the Sun is along that life-cycle timeline?
The sun is currently 5.5 billion years of gradual warming away from becoming a red giant. Then it will be a planetary nebula and a white dwarf.
2. How faint was the sun in early Earth history (~4.5-3.5 billion yrs ago) relative to today?
The sun's luminosity was around 70-75% compared to the 100% luminosity we have today
Describe how atmospheric CO2 can be controlled by mountain uplift followed by chemical weathering of these mtns - use examples of uplift and climate at time Pangaea was forming and at the time the Himalayan mountains/Tibetan plateau where forming. Why does uplift cause cooling? How does physical weathering promote chemical weathering?
The uplifts greats many smaller surfaces (physical weathering ) which then causes chemical weathering like an already sliced apple.
Describe the paleogeography of the Cretaceous: with respect to distribution and positions of land and sea and sea level.
There was a polar land mass but no ice, sea level was high and small amount of exposed land mass.
Were there ice sheets on Antarctica in the Cretaceous? Were there forests there?
There was no ice, but there was New Zealand time vegetation and forest in Antarctica.
8. Why wasn't life the primary regulator of climate 3 to 4 billion years ago?
There were no signs of life (according to fossil records) until 3 billion years ago.
What were the CO2 levels during the Cretaceous? How much higher were CO2 levels in the Cretaceous than today?
They were a little over 4000 ppm. They were around 3500 ppm more.
7. How was the glaciation of Antarctica an example of a threshold event? When did this happen?
This glaciation was an example of a threshold event because there was no ice at all until the drastic cooling from the slowing of sea floor spreading + weathering. Once it became cool enough the glaciation took place quickly 45-15 million years ago explained in threshold event.
How is the stable oxygen isotope record of benthic foraminifera a biogeochemical proxy for past climate change? (what is the bio, and what is the geo, and what is the chem part?)
Times that were cooler will have more O18 shells whereas time that is warmer will have more O16 shells
12. What types of methods were used in Owens Lake to determine age?
Using a spinner magnetometer, tephrochronology (ash studies), and radiocarbon +3analysis.
Why would weathering of organic C exposed at the Earth's surface put CO2 back into the atmosphere, but weathering of typical bedrock (non-organic C) take CO2 out of the atmosphere?
Weathering of C exposed releases the Carbon that was originally in the rock. Weathering of non-organic C takes co2 out of the atmosphere because it breaks up the rock, creating more surface area to take in co2. The weathering of organic carbon (plants, peat coal, oil) on mountains goes through oxidation and produces H2O and CO2; the silicate rock is exposed to the elements at the surface, it takes CO2 and H2O, which reacts with the bedrock and moves into the ocean
7. Do you only go with one way to determine age or multiple ways if you can? Why?
You can go with multiple ways: Radiometric dating (based on the fixed decay rate of radioactive isotopes), fossils, paleomagnetic reversal patterns, special horizons in layers, geochemical patterns, counting layers. You use multiple ways because just one won't necessarily tell the whole story, or other things could affect it.
9. What are index fossils?
a fossil that is useful for dating and correlating the strata in which it is found, best for age determination (narrow time period).
What is meant by isotopic "fractionation"?
describes processes that affect the relative abundance of isotopes, The differences of mass between O18 and O16 causes fractionate or partially separate water containing o18 from water containing o16.
17. What lessons should we learn about climate change based on the PETM?
Look at the δ18O graph: can you identify times of rapid warming vs rapid cooling? Gradual warming and gradual cooling? Based on the handout did the Northern and Southern hemispheres transition to the current icehouse time simultaneously?
google these
6. How do ocean "gateways" result from plate tectonics? How do ocean gateways result in changes in ocean circulation? How did the ocean gateway between Antarctica and Tasmania impact heat transfer from the subtropics to Antarctica?
google this
Are we in an icehouse world or a greenhouse world today?
icehouse
What climatic conditions produce an increase in benthic foram δ18O? A decrease of benthic foram δ18O? .
increase- more ice/ cooler ocean. Decrease- less ice/warmer ocean
The overall temperatures in the Cretaceous were warmer than they are today. But were there certain latitudes that showed even greater relative warming?
lower latitudes were slightly higher in temp but higher latitudes (the poles) were significantly warmer than today.
If other data indicates there was no ice on continents, then is it reasonable to assume any changes in δ18O during that time are because of temperature changes?
yes