GEO 1308 Exam 2

Comprehensive practice flashcards detailing paleoclimate proxy methods, orbital Milankovitch cycles, the Last Glacial Maximum, deep-time greenhouse/icehouse worlds, Neolithic agriculture, and the Great Acceleration.

How do direct instrumental climate records differ from paleoclimate proxies?

Direct instrumental records rely on measurements from scientific instruments during historical times, whereas paleoclimate proxies provide indirect evidence of ancient climatic conditions preserved within natural geologic and biological archives.

Why can polar ice cores provide a direct measurement of past atmospheric composition rather than a proxy estimate?

As annual snowfall accumulates and compacts into glacial ice, pockets of air are sealed as bubbles, preserving direct physical samples of the ancient atmosphere that can be analyzed for greenhouse gases like $CO_2$ and $CH_4$.

How does the density of the microscopic leaf pores shown here relate to atmospheric carbon dioxide concentrations?

Fossil leaf stomata exhibit an inverse relationship with carbon dioxide levels: lower stomatal density reflects higher atmospheric $CO_2$, while higher stomatal density reflects lower atmospheric $CO_2$.

How does the annual growth ring thickness in temperate tree trunks record paleoclimate data?

Individual tree ring width corresponds to spring growth rates, where wider rings record wet, favorable growth conditions and narrower rings record drought conditions.

What is the physical mechanism causing oxygen isotope fractionation between $^{16}\text{O}$ and $^{18}\text{O}$ during evaporation and condensation?

Because $^{18}\text{O}$ is heavier than $^{16}\text{O}$, water containing $^{16}\text{O}$ evaporates more easily with less energy, whereas water containing $^{18}\text{O}$ condenses more readily.

Why does ocean water become enriched in $^{18}\text{O}$ during cold glacial periods?

Light water molecules containing $^{16}\text{O}$ evaporate preferentially, travel toward the poles as precipitation, and become trapped on land in growing continental ice sheets, leaving the remaining seawater with a higher ratio of $^{18}\text{O}$ to $^{16}\text{O}$.

Which biological and mineral archives incorporate the marine $^{18}\text{O}/^{16}\text{O}$ ratio into solid calcium carbonate ($CaCO_3$)?

Foraminifera shells, marine mollusks (seashells), limestone deposits, coral reefs, herbivore tooth enamel, and cave speleothems (stalagmites and stalactites).

Why is the Northern Hemisphere more climatically sensitive to changes in incoming solar insolation than the Southern Hemisphere?

The Northern Hemisphere contains $68\%$ of Earth's land area compared to only $32\%$ in the Southern Hemisphere, and because land has a lower heat capacity than water, it warms and cools much faster, facilitating the ice-albedo feedback.

What is Milankovitch obliquity, and what is its periodicity?

Obliquity is the wobble of Earth's axial tilt relative to its orbital plane, shifting by $2.4^\circ$ over a $41{,}000\text{-year}$ cycle.

What is orbital eccentricity, and over what cycle does it vary?

Eccentricity is the variation in the oval shape of Earth's orbit around the Sun (the ratio of long axis to short axis), varying between $0.0034$ and $0.058$ over a $100{,}000\text{-year}$ cycle.

What orbital cycle controls whether the Northern Hemisphere points toward or away from the Sun during perihelion?

Precession of Earth's axis, which operates on a $26{,}000\text{-year}$ cycle (with equinox precession cycles of $19{,}000$ and $23{,}000\text{ years}$).

How do constructive and destructive interference among Milankovitch cycles affect glacial-interglacial transitions?

When the cycles of obliquity, eccentricity, and precession are in phase, their effects on solar insolation are amplified; when out of phase, their climate effects are dampened.

What physical behavior allows glaciers to move downhill under their own weight?

Glacial ice behaves like a highly viscous liquid when placed under tremendous pressure over long timescales, flowing downslope under gravitational force.

What distinct geological evidence of past glacial movement is shown on this exposed bedrock?

Glacial striations, which are linear gouges and scratches carved into bedrock by rocks and debris embedded in the base of a moving glacier.

What glacial features are mapped across the Midwestern United States in this diagram?

End moraines (terminal and recessional moraines), which are ridged accumulations of unsorted debris deposited at the margin of a glacier.

What process causes small earthquakes and uplift in northern regions previously covered by massive Pleistocene ice sheets?

Post-glacial isostatic rebound, which is the slow vertical relaxation and uplift of Earth's crust in response to the removal of heavy ice sheets.

How much colder was global average surface temperature during the Last Glacial Maximum (LGM) compared to today?

Approximately $8\,^\circ\text{C}$ ($14.4\,^\circ\text{F}$) colder globally, with regional temperature anomalies reaching up to $-14\,^\circ\text{C}$ ($25.2\,^\circ\text{F}$).

By approximately how much did sea level drop during the Last Glacial Maximum?

Approximately $120\text{ feet}$ ($37\text{ meters}$), exposing extensive continental shelves and land bridges between landmasses.

Why was the global climate generally drier during the Last Glacial Maximum than it is today?

Colder air holds less atmospheric moisture, and lower global temperatures suppressed sea-surface evaporation, expanding deserts, steppes, and taiga biomes.

Which extinct cold-adapted megafaunal species is depicted in this reconstruction?

The woolly rhinoceros (Coelodonta).

How did the climate and vegetation of Central Texas during the Last Glacial Maximum differ from its modern environment?

Central Texas was cooler and wetter, covered primarily in extensive open grasslands that supported Columbian mammoths, camels, horses, and saber-toothed cats, rather than modern shrublands.

Why does the deep-sea sediment climate record only extend back roughly $200\text{ million years}$ (Jurassic Period)?

Plate tectonics continuously recycles oceanic crust; older, dense oceanic lithosphere is subducted back into the mantle at convergent plate boundaries.

What is the defining distinction between an 'Icehouse World' and a 'Greenhouse World'?

An Icehouse World possesses permanent ice sheets at one or both poles (encompassing both glacial and interglacial states), whereas a Greenhouse World lacks permanent polar ice and features global temperatures $+8\text{ to }10\,^\circ\text{C}$ warmer than today.

What fossil evidence proves that polar regions experienced tropical to warm temperate conditions during the Cretaceous and Devonian periods?

Fossils of cold-blooded reptiles, herbivorous dinosaurs, and tropical plants in Cretaceous Antarctica, alongside Devonian amphibian fossils found in Greenland.

What catastrophic environmental triggers drove the Permian-Triassic Mass Extinction ($250\text{ million years ago}$)?

Intense flood basalt volcanism from the Siberian Traps burned through vast coal and petroleum deposits, releasing $170{,}000\text{ gigatons of }CO_2$ over $60{,}000\text{ years}$, pushing global temperatures to $34\,^\circ\text{C}$, ocean surface waters to $45\,^\circ\text{C}$, and inducing widespread ocean anoxia.

What positive climate feedback shown here is thought to have exacerbated the Paleocene-Eocene Thermal Maximum (PETM)?

The destabilization and release of submarine and permafrost methane hydrates (clathrates) in response to initial ocean warming, which released up to $10{,}000\text{ gigatons of carbon}$ and triggered ocean acidification.

How do modern anthropogenic carbon emission rates compare to those during the PETM warming event?

Modern emissions are rising far faster, releasing up to $25\text{ petagrams of carbon per year}$, compared to a peak rate of approximately $1.7\text{ petagrams of carbon per year}$ during the PETM.

What ecological role did southern European LGM glacial refugia play, as shown on this map?

They provided sheltered pockets of milder climate in southern peninsulas (Iberian, Apennine, Balkan) that allowed human hunter-gatherers and temperate flora and fauna to survive and later recolonize northern latitudes.

What was the Younger Dryas, and approximately when did it occur?

A sudden, abrupt cooling event in high northern latitudes occurring approximately $12{,}800\text{ to }13{,}000\text{ years ago}$, likely triggered by an interruption of thermohaline ocean circulation that temporarily reversed post-glacial warming.

What climatic change characterized low-latitude regions such as Northern Africa after the Last Glacial Maximum?

Monsoon systems intensified, producing the African Humid Period (or 'Green Sahara') and transforming arid low-latitude landscapes into productive, vegetated ecosystems.

When did the Holocene epoch begin, and what characterized its climate relative to the Pleistocene?

The Holocene began $11{,}600\text{ years ago}$ and has been characterized by relative climatic and temperature stability compared to the glacial volatility of the Pleistocene.

Which major agricultural innovations enabled early permanent Neolithic settlements to stabilize food yields against natural climate variability?

Plowing technologies to mechanically manage soil nutrient quality and irrigation infrastructure to provide a reliable, controlled water supply independent of irregular rainfall.

Which prolonged climatic event contributed to the abandonment of the Ancestral Puebloan cliff settlement shown here?

A severe $26\text{-year}$ drought around $1280\text{ AD}$, identified through tree-ring precipitation reconstructions, which led to the collapse and abandonment of Mesa Verde.

What ancient civilizations collapsed in part due to multi-decadal droughts around $2200\text{ BC}$, $1200\text{ BC}$, and $800\text{ BC}$?

The Akkadian Empire (~$2200\text{ BC}$), the Late Bronze Age Mediterranean civilizations (~$1200\text{ BC}$), and the ancient Maya civilization (~$800\text{ BC}$).

What human activities altered the carbon cycle and greenhouse gas concentrations prior to the Industrial Revolution?

Deforestation starting ~$8{,}000\text{ years ago}$ reduced biomass and emitted $CO_2$, domesticated ruminant livestock emitted $CH_4$, and land cultivation (such as flooded rice paddies) disrupted soil carbon burial while emitting additional methane.

Why did early industrial societies transition from wood to coal as their primary thermal energy source in 18th- and 19th-century Europe?

Widespread deforestation in the 17th century created regional wood shortages and escalating costs, prompting the switch to coal, which is nearly twice as energy dense as wood.

What environmental conditions during the Carboniferous Period led to the formation of extensive coal beds?

Ancient swamp forests produced thick accumulations of dead plant litter in stagnant, oxygen-poor (anaerobic) peat bogs, preventing microbial decomposition and preserving carbon under heat and pressure over time.

What was the initial primary industrial application of James Watt's improved steam engine in $1776$?

Pumping water out of deep coal mines to allow easier and deeper extraction of coal seams.

What biological material forms crude oil and natural gas, and how do they accumulate?

Marine plankton buried in oxygen-depleted marine sediments under heat and pressure, producing liquid hydrocarbons and gas that migrate into the pore spaces of permeable sedimentary reservoir rocks.

Where and when was the first commercial oil well drilled in the United States?

Titusville, Pennsylvania, in $1856$ (or $1859$).

Why was natural gas largely treated as an unusable waste byproduct before the $1920\text{s}$?

The absence of high-pressure pipeline networks made gathering, containing, and transporting gaseous hydrocarbons too technologically difficult and expensive, leading producers to flare it off.

What is 'The Great Acceleration', and when did it begin?

An exponential, synchronized surge in human socioeconomic activity, resource consumption, industrial output, and Earth-system impacts that began in the mid-20th century (post-World War II).

Which primary Earth system metrics experienced sharp post-1950 upward inflections as part of the Great Acceleration?

Atmospheric concentrations of $CO_2$, $CH_4$, and $N_2O$, global surface temperature anomalies, ocean acidification, marine fish capture, and tropical forest loss.