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Geology Test 2
| Question | Answer |
|---|---|
| What is paleoclimate and why is it useful for understanding climate change? | Paleoclimate is the study of past climate change involving collecting data of past climate change and related geologic evidence for understanding the causes of past climate change. It provides a broader perspective on the range of climate change |
| What is the uniformitarian theory in geology? Why is it important? | The idea that the present is the key to the past. we can study the processes involved in the modern climate system and use them to understand the types of processes that operated in the past, and understand why climate changes in the geologic past. |
| What are examples of geologic records of climate change? What are examples of long-term and short-term records? | They include sedimentary rocks, ice cores, marine sediments, lake sediments (all long term records), as well as tree rings, corals, cave deposits, and young sediments and ice layers (all short-term records). |
| What is the Snowball Earth theory? When did major glaciations of the Proterozoic Eon occur in the past? | The theory that ancient glaciations of the Proterozoic Eon covered almost the entire Earth in ice (ice sheets and sea ice). They occurred at 2.2 Ga (billion years ago), 730 Ma (million years ago), and 650 Ma. |
| What is the geologic evidence of Snowball Earth glaciations? | Mostly consists of sedimentary rock deposited by glaciers (tillite) and by icebergs (ice-rafted debris/dropstones). Importantly, magnetic properties of these sedimentary rocks help to reconstruct their latitude at the time when they were deposited. |
| What is the likely cause of Snowball Earth glaciations and what caused them to end? | The runaway freeze was caused by a decline in atmospheric CO2 and the ice-albedo effect. Needed reduced greenhouse effect for low temperatures at low latitudes. Ended with a rise in atmospheric CO2 caused by intense volcanic activity. |
| During the Phanerozoic Eon, what has been the most common state of the Earth – greenhouse or icehouse? How do we know this? | The most common state has been a greenhouse, with a few icehouse intervals (including the last 36 Ma). We know this by studying the geologic record, mostly sedimentary rocks with fossils and geochemical proxies, all indicating mostly warm climates. |
| What is the polar position hypothesis? How does it hold up to hypothesis testing? | The hypothesis that every time in Earth history when a continent has been present at the north or south pole, an ice sheet would form at the pole. This does not hold up to hypothesis testing. |
| What are examples of biotic, geochemical, and geologic proxies for atmospheric CO2 during the Phanerozoic Eon? | Biotic proxies include fossils of primary producers that gain mass through photosynthesis. Geochemical proxies include carbon isotopes in soil and ocean water. Geologic proxies include evidence of sea level changes related to global volcanic activity. |
| What is the overall trend of climate change during the last 65 million years? How do we know this? | Warming at the start of the Cenozoic Era, followed by cooling after 50 Ma. We know this from oxygen isotopes of fossils preserved in marine sediments. |
| Which reservoirs of water have the greatest δ18O values? Which have the lowest? Explain why these differences exist. | Ocean water has the greatest d18O values and snow/ice have the lowest. Fractionation of oxygen isotopes during phase changes in the global water cycle are the reason why these differences exist. |
| When did the Antarctic ice sheet form? When did the Greenland ice sheet form? How do we know this from geochemical and geologic proxies? | Antarctic Ice Sheet formed 36 Ma. Greenland Ice Sheet formed at about 7 Ma. From oxygen isotope records indicating changes in ice volume and from the appearance of ice-rafted debris in marine sediment collected just offshore of Antarctica and Greenland. |
| What is the Paleocene-Eocene Thermal Maximum (the PETM)? What climate changes accompanied this event? | A rapid change in climate at the boundary between the Paleocene and Eocene Epochs of the Tertiary Period. Major warming occurred during this time over a period of only about 8000 years. |
| What paleoclimate records indicate that high carbon dioxide levels were responsible for the PETM? | The negative shift in del13C in marine sediment along with the decrease in carbonate-rich sediment at the start of the PETM. Del18O records indicate rapid warming at the start of the PETM, by themselves don't indicate that atmospheric CO2 levels were high |
| What tectonic forcings of climate change may have contributed to the long-term cooling trend of the last 50 million years? | a slowdown in plate movements and attendant volcanic activity. continent-continent collisions across southern Asia and Europe. caused uplift of a large area that likely accelerated chemical weathering rates, caused CO2 to go from atmosphere to ocean |
| What feedbacks in the Earth climate system may have contributed to the long-term cooling trend of the last 50 million years? | Appearance of glaciers on the continents, especially after 36 Ma, was a positive feedback. Glaciers advance and decay over time, that grind rocks and and produces reactants for chemical weathering reactions. Helps reduce CO2 levels in the atmosphere |
| What is the Quaternary Period? What characterizes the Earth climate system during this time interval? | The last 2.6 million years of Earth history. Cold intervals with big glaciers are the norm for this interval. |
| What is the Milankovitch theory of insolation forcing of global ice volume changes? | The geometry of Earth orbit around the Sun changes due to forces of gravity. Changes in eccentricity, obliquity, and precession result in changes in incoming solar radiation that cause climate change. This caused ice sheets to grow and decay. |
| What has a greater affect on incoming solar radiation at high latitudes, eccentricity or obliquity of the Earth orbit? | Obliquity - this causes huge changes in incoming solar radiation, whereas eccentricity doesn't vary too much but causes insolation changes at all latitudes. |
| What are the periods of eccentricity, obliquity, and precessions cycles, and how does each cycle affect summer insolation? | Eccentricity = 100 kyr and 413 kyr, affects the Earth-Sun distance, affects insolation. Obliquity - 41 kyr, affects the axial tilt angle, increases or decreases seasonality; Precession - 23 kyr, the wobble of the Earth rotational axis, affects the timing. |
| What is the evidence that global ice volume changes were driven by obliquity changes prior to 1 million years ago? | The frequency of glaciations and interglaciations was 41 kyr and times of tilt-angle minimum preceded glaciations and tilt-angle maximum preceded interglaciations. |
| How did the frequency of glaciations and interglaciations change from prior to 1 million years ago to after 1 million years ago? | The frequency changed from 41 kyr to 100 kyr on average, although the frequency of the past 500 kyr has varied a lot compared to prior to 1 Ma. |
| Over the past 150,000 years, how have obliquity and precession changes affected global ice volume? | They have caused changes in ice volume, but only low amplitude changes compared to the high amplitude changes occurring every 100 kyr on average. |
| What are the two stable isotopes of carbon? How does δ13C vary among the carbon reservoirs? | C12 more and C13 less. The del13C of reservoirs are organic carbon has low del13C values (-22 to -20 per mil), atmospheric CO2 has low values (-6 to -4 per mil), and inorganic carbon in ocean water has the highest values of 0 to 1 per mil. |
| By what pathways can carbon get into the oceans? What happens to ocean water when CO2 is dissolved in it? | Carbon can enter the ocean by dissolution and photosynthesis. Dissolved CO2 makes ocean water more acidic. |
| Where was the biggest ice sheet to form during the last glaciation (a.k.a., the last ice age)? | North America - the Laurentide Ice Sheet. |
Created by:
pmitchell44